MegaSTe hardware problems -help locate it please!

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Re: MegaSTe hardware problems -help locate it please!

Postby Fujiyama » Wed Sep 13, 2017 6:37 pm

Finally a few free moments to work on the MSTE again :D

In preparation for recapping the PSU I've measured the various voltages and they all seem to be within spec. How "clean" and stable the voltage rails are is another question which I have no idea.
Next I've started to check the IC sockets and have so far removed and re-inserted all the DIL type ICs. The PLCC chips are another story as I need some more time for that, given that I don't have a dedicated PLCC extractor tool, but very carefully pry them out.

It may very well be that there is some contact problem(s) somewhere, but at the same time things seem to point towards the opto-isolator (U-302). I say this because I finally got the computer to boot, so I tried out Notator again, but as before no MIDI input. But then I realized (I might have mentioned this before) that the missing keyboard response (no click while the TOS 2.06 memory test is running), and no response when pressing the keys as well as missing mouse response had to do with having the MIDI IN cable connected from the synth.
Furthermore I attached my old MIDI input-selector box (which I also added a "soft THRU"/"hard THRU" switch to, utilizing the non-standard MIDI connection so I could play other synths without running a sequencer program) and the "MIDI activity" LED I added lights up constantly!
Now, this is a DX-7 I attached, which is know to output an "active sensing" message, but this should flash the LED, not light it constantly. To me, this indicates a short between the MIDI IN and OUT jacks. An estimated guess tells me the opto-isolator is broken.
I decided to try out my MIDI switchbox before soldering new MIDI cables for testing.

Another discovery: I mentioned that the MSTE schematic says that U-302 is a Sharp PC-900, and that the one actually used was another type. Well, I misread the markings. It actually says H11L3 (not HIL3 as previously quoted), and that IC is still available for purchase without going to eBay etc. So that's good news. So what do you think? Does it sound like a broken opto-isolator could be the reason for my problems? I could desolder it, put in a socket and try out a new H11L3.

Well, that's a little update. I'm not giving up quite yet :wink:
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Re: MegaSTe hardware problems -help locate it please!

Postby siriushardware » Fri Sep 15, 2017 5:18 pm

The default state for the output device in the optocoupler is OFF, so that means that with the power on to the machine and no MIDI IN activity you should measure a steady HIGH state (5V) on pin 4 of U302.

If you then connect a midi source and generate a blizzard of MIDI activity (rolling the pitch bend wheel back and forward is an excellent way to do that) you should see the voltage temporarily lowering. Using a logic probe or a scope would be a better way to observe this - then you would see a train of low pulses coming out of the opto output whenever there is a big burst of MIDI activity.

If you see a steady LOW (0V) on the opto output regardless of whether there is MIDI IN activity then it is possible that the opto output has failed and is pulling that point in the circuit low.

If you do find a steady low state on pin 4 of the opto, remove the opto from the PCB and make the measurement again.

If the voltage on the pad normally occupied by pin 4 of the opto has now risen to 5V, your opto is faulty.

If you've removed the opto but you still have a low (0V) state on the pad normally occupied by pin 4 of the opto then your problem is elsewhere - could be that the pullup resistor (R307, 4K7) is cracked / open circuit. The input of U301F would also normally be a suspect but I believe you've already changed U301. It is also possible that the input (pin 2) of the 68B50 ACIA has failed short-circuit / low resistance down to 0V, but let's not go there for the moment.

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Re: MegaSTe hardware problems -help locate it please!

Postby Fujiyama » Mon Sep 18, 2017 8:33 pm

That's useful info as always which I'll get back to, but I've made some new discoveries.
First, I replaced the H11L3 opto-coupler (U302) with an IC-socket, then put it back in, but guess what? It makes no difference if the opto-isolator is present or not! The LED of my MIDI input selector box lights constantly regardless, so I suppose there might be a short-circuit somewhere.

Just to make sure there wasn't something wrong with the box (which is probably 25 years or so old) I pulled out my trusty old STe (works fine except its floppy drive and doesn't have a MonSTer board installed yet, as planned, which has completely spoilt me with impatience when booting and starting up software!) and tried out what you suggested earlier: set the box to "MIDI THRU" mode, setting the keyboard synth to "local off" then play a few notes -yes! it does play the synth, so it works fine. By setting it to the standard "MIDI OUT" mode it wouldn't play anything as expected.

About the MIDI input selector box: I finally took the time to open it up, check the wiring and draw up a schematic which I'm enclosing here.
Its main function is (or should I say "was" as I since then replaced it with a Roland A-880 MIDI patchbay/merger) to allow sysex dumping from a variety of MIDI modules' OUTs without unplugging cables. The everyday setting is to have it selected to the master keyboard input, which in turn controls a variety of MIDI modules.
I also took advantage of the rather unique (and may I add; non-standard) MIDI OUT port so that by setting it to the (non-standard) "THRU" mode I could play around with my synths without having to run any MIDI sequencer (or "software THRU" type programs) first. As far as I remember the computer has to be powered on though, but that's no biggie.
By switching it over to the normal MIDI "OUT" mode I would have to run a MIDI sequencer or other software in order to play the MIDI modules attached to the OUT of the ST.
MIDI IN selector with Atari ST THRU.png

The way I attached MIDI cables for testing via the box was as follows:

Synth OUT to box IN#1
Box OUT to synth IN
Box "ST OUT" to Atari STe OUT
Box "ST IN" to Atari STe IN

The synth was set to "Local OFF" and the switch on the box set to "THRU mode".
The LED dimly flashed whenever I played something on the keyboard.
Good thing I have two Ataris for troubleshooting!

I've taken a closer look at the MSTE schematic around the MIDI IN section and something puzzles me....
mste_MIDI_section.png


For some reason I found pin 2 of U302 (the opto-isolator) to connect to GND! And that's with the IC removed from the socket!!!
So I traced the path from pin 5 of the MIDI IN connector, through L306 and there it was! I don't know exactly how inductors work or their purpose here, but unlike the schematic says, they both (one's connected to pin 4 of the MIDI IN connector, seemingly marked "L309", but according to the actual MSTE PCB silkscreen it should be "L305") have three pins, not just two!
The centre pin of L306 goes to GND -it's not a short circuit but an actual trace. I don't know what to make of that, but apparently it was designed that way.
Anyway, like I said the MIDI input selector box's LED lit up constantly when connected to the MSTE, even without the opto-isolator IC present, so I suspect there's a short circuit or malfunctioning component somewhere along the line. I don't know if this has anything to do with the sometimes working keyboard/mouse (and sometimes not, likewise the keyboard click sound) but it does point in the direction of a bad connection at the very least.

I've just received a missing connector for my oscilloscope, so when that's in place I'll check what you suggested and look closer at R307 as well.
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Re: MegaSTe hardware problems -help locate it please!

Postby siriushardware » Tue Sep 19, 2017 12:18 am

Just check one thing: With -nothing- connected to the MIDI IN port on the computer, do you still have your measured short from MIDI IN pin 5 to 0V on the MSTe? I just want to be sure that the short you are measuring is not actually down the connected MIDI cable, through the equipment at the other end and connected to 0V on the MSTe via the shared mains earth connection.

As you've noticed L305 /L306 are only supposed to have two actual connections. However, components with only two pins are prone to wobble back and forth so sometimes coils / inductors / transformers have extra legs which are not connected to any part of the coil winding. Their job is just to provide more solder anchor points to the PCB.

If the schematic is correct, there should not be a direct connection from any part of the inductor L306 to 0V. If you really do have a connection to 0V through the inductor, the inductor is faulty - it may be that there is a short between the coil winding and the third pin.

So here's the good news, L305 and L306 are non-essential from the point of view of MIDI functionality. The ST has lots of sharp-edged high frequency waveforms running around inside it, and if allowed to exit from the machine via any of the long cables connected to it, these signals could interfere with radio reception in the local area. The purpose of L305 and L306 is to filter out radio frequency interference and prevent it from travelling out through the MIDI IN port and being radiated by the MIDI cables.

For diagnostic purposes, you can remove L305 and L306 and replace each one with a wire link to see if that fixes your problem. Note that if you do, you should ignore the third pin which is soldered to the ground plane on the PCB. Your wire links should connect the other two pins together, so that one wire link connects MIDI IN pin 5 directly to opto pin 2, and the other wire link connects MIDI IN pin 4 directly to R308.

You don't need a scope to check R304, the pullup resistor. With the power off, measure the resistance across R304 in-circuit. It should be 4.7K, or something lower than 4.7K. If you get a reading higher than 4.7K, desolder one end of R304 or remove it altogether and measure the resistance of the resistor by itself.

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Re: MegaSTe hardware problems -help locate it please!

Postby czietz » Tue Sep 19, 2017 5:51 am

siriushardware wrote:As you've noticed L305 /L306 are only supposed to have two actual connections. However, components with only two pins are prone to wobble back and forth so sometimes coils / inductors / transformers have extra legs which are not connected to any part of the coil winding. Their job is just to provide more solder anchor points to the PCB.


No, actually the third pin of these components is not just for mechanical support. The schematic gives it away: These are not simple inductors, but T-type EMI filters, comparable to this one:
Image

I.e. even though they are marked Lxxx, they consist of two inductors and a capacitor like this:
Image

Hence, it is perfectly normal that the center pin is connected to ground.

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Re: MegaSTe hardware problems -help locate it please!

Postby Fujiyama » Tue Sep 19, 2017 11:40 am

What Czietz is saying makes sense (given the circuit trace from the middle-pin of the inductor which goes to the GND plane) but also makes it all more confusing.
I will do some more troubleshooting tonight and compare the results with that of the plain STe. Comparing the two schematics they appear to be identical when it comes to the MIDI ports.

And yes, Siriushardware; I checked with nothing connected to the MIDI ports, and with power off (actually I think had removed the motherboard from its case for checking the solder connections underneath for any shorts or cold joints). That's why I was so surprised to find that MIDI pin going to GND as nothing external (even the monitor, hard drive etc.) was connected.
It'll be interesting to see how it compares with the STe MIDI IN port.

UPDATE: I haven't had time to do any extensive tests, but using a multimeter set to continuity testing I found out that on the STe, none of the MIDI IN port pins are connected to GND and the MIDI OUT portonly had pin 2 connected to GND. Just like the schematic says it should.
Looks like I should have a closer look at the inductor in the MSTE and compare it with one of the other inductors.
Are they all the same? The schematics say nothing about their values.
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Re: MegaSTe hardware problems -help locate it please!

Postby siriushardware » Tue Sep 19, 2017 5:41 pm

czietz wrote:The schematic gives it away: These are not simple inductors.


True, although the fact that the drawing represents them as normal inductors is misleading. But yes, I've only just noticed the words 'T Filters' near those components.

In the light of that clarification from Czietz, it is actually possible that the capacitor in the T-filter assembly has gone short circuit.

You can verify this by taking out the suspect coil/filter and measuring the resistance from each terminal of the component to the others. Your meter should see a dead short, more or less, between two of the pins. From those two pins to the third pin (the one which normally goes to zero volts on the PCB) there should appear to be infinite resistance, although you may see a brief flash of lower resistance when you first connect the meter. If all three pins appear to be constantly shorted to each other the device is faulty.

If that proves to be the case, what I said before still applies - these components are just interference filters and you can bypass a suspected faulty one by linking from one side to the other and leaving the third (0V connected) PCB hole unconnected. If that solves the problem, by all means try to source a replacement filter.

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Re: MegaSTe hardware problems -help locate it please!

Postby czietz » Tue Sep 19, 2017 8:13 pm

Fujiyama wrote:Are they all the same? The schematics say nothing about their values.


The STE (not MegaSTE) service manual mentions them as "noise filters" and gives several possible suppliers. Luckily, for the TDK part number ZJSR5101-102 a datasheet can still be found: http://pdf1.alldatasheet.com/datasheet- ... 1-102.html

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Re: MegaSTe hardware problems -help locate it please!

Postby Fujiyama » Wed Sep 20, 2017 12:03 pm

Useful info about the filter, Czietz. Thanks for that and the datasheet.
Given that the schematic looks identical between the two machines (STe and Mega STe) I assume the filters used are the same.
The one I've just removed is marked "TDK 102", so the ZJSR5101-102 part number appears to be correct for this component.

I had actually written a followup ready to be posted when I realized I had removed and measured the wrong filter (L305 instead of L306) :lol:
Well, at least I got to check both a working and a failed one for comparison!

Needless to say, I believe I've found the culprit: L306 is indeed faulty according to what you, siriushardware, suggested.


siriushardware wrote:In the light of that clarification from Czietz, it is actually possible that the capacitor in the T-filter assembly has gone short circuit.

You can verify this by taking out the suspect coil/filter and measuring the resistance from each terminal of the component to the others. Your meter should see a dead short, more or less, between two of the pins.


Yes, it measure 9 Ohms between each of the outer pins
(EDIT: that reading goes for both the faulty and working filter)


From those two pins to the third pin (the one which normally goes to zero volts on the PCB) there should appear to be infinite resistance, although you may see a brief flash of lower resistance when you first connect the meter. If all three pins appear to be constantly shorted to each other the device is faulty.


Neither!
My digital multimeter doesn't indicate anything at all (the display doesn't change at all when the pins touch the pins), not even for a brief moment when measuring between the middle and one of the outer pins, and the middle pin along with the other pin. I've tried with the meter set to auto-range as well as manual ranges. Still no response. One possibility is that "OL" (overload) which is shown on the meter's display by default (when nothing is measured) actually does measure resistance, but beyond what the meter is capable of (i.e. infinite resistance as you pointed out).

Out of curiosity I set my meter to capacitance mode, which gave me 1.155nF between either end pin along with the middle pin. There was no reading when measuring the capacitance between just the two outer pins, which of course makes sense when I see how the filter is constructed.
I'm puzzled :?
But with the datasheet saying that the "-102" marking means that it contains a 1000pf capacitor (which translates into 1nF) it appears that the capacitance at least is within specs.
EDIT: the above readings were all for the working one....
but checking the faulty one (L306) I measured 1.77 Ohms between either outer pin and the middle pin, so in essence it's short-circuited to GND, just as you suggested it might be. Good catch! :thumbs:
There's no capacitance reading between either outer pins and middle pin (nor between just the two outer pins for that matter).
And as expected, the MIDI IN pin 5 to GND connection is now gone!


If that proves to be the case, what I said before still applies - these components are just interference filters and you can bypass a suspected faulty one by linking from one side to the other and leaving the third (0V connected) PCB hole unconnected. If that solves the problem, by all means try to source a replacement filter.


Yes, I'll give that a go, if for no other reason than to figure out if the MIDI pin 5 short to GND goes away or not.
EDIT: and away it went! At the moment my motherboard is removed and disconnected, but I'll solder a wire across the two outer pins of where the L306 filter goes and see what happens when I power it all up again. I suppose that if there are any spikes which the filter should catch, the opto-isolator will blow (and nothing past it) which is fine as I've now found out that the H11L3 is readily available.

In the meantime, does anyone know a (legit) source for the ZJSR5101-102 filter manufactured by TDK? A quick web-search only results in numerous "sourcing" sites, and from what I've heard they often operate with poor quality fakes instead of the real thing.
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Re: MegaSTe hardware problems -help locate it please!

Postby dhedberg » Wed Sep 20, 2017 12:14 pm

Daniel, New Beat - http://newbeat.atari.org

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Re: MegaSTe hardware problems -help locate it please!

Postby Fujiyama » Wed Sep 20, 2017 12:43 pm

Yes, that appears to be a legit dealer who has them. But being a U.S. company, do you know how much they charge for shipping overseas? U.S. companies usually overcharge quite a bit in my experience unfortunately. I'm not able to check the shipping costs before creating a username and logging in.

On a different note it appears I'm not the only one who's had problems with those filters inside an Atari ST (scroll down to almost the bottom of the page).

UPDATE: It's working!!! MIDI IN on the Mega STe is working again, and so far I've been able to boot without any issues as before (no response from the keyboard or mouse). I will keep on testing, but so far it's looking good :D
Thanks to everybody joining in for the invaluable help I've been given!
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Re: MegaSTe hardware problems -help locate it please!

Postby Fujiyama » Wed Sep 20, 2017 8:17 pm

Another thing (I'm on a roll here)...
I had a closer look at the "No stereo sound available" message when trying to open the "Sound" CPX module and strangely I was able to access it after disabling (turning off) DIP switch 8 and rebooting!
megaste_DIP8.png


I'm pretty sure I've had it enabled in the past in order to enable DMA audio, but I could of course be wrong. I tried to find documentation on this but there wasn't much in terms of hard facts other than a discussion thread here which points to the same DIP switch. DIP switch 7 on the other hand is documented several places (such as Atari's official 1.44MB disk drive upgrade) in order to see the "High density" desktop format option.

I metered the switch and indeed, pin 11 of U705 (74LS244) goes to GND when enabled. Does anyone have any more info on DIP switch 8?

UPDATE: seeing that it works fine with DIP #8 OFF I must have just heard that this switch handles DMA audio, so I assumed the ON position would mean DMA audio ON while it's in fact opposite! As my STe also has similar options (8 solder pads instead of 8 DIP switches) and none of them were enabled (wires soldered across) but with DMA audio still enabled this makes perfect sense.
So I conclude the following when it comes to the Mega STe DIP switch block:

DIP #7 ON = 1.44MB high density desktop format option in TOS 2.06 turned ON
DIP #8 OFF = DMA audio ON
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Re: MegaSTe hardware problems -help locate it please!

Postby Fujiyama » Thu Sep 21, 2017 6:12 pm

dhedberg wrote:How about Quest Components?
https://www.questcomp.com/QuestDetails. ... partsearch


I just registered with them (in order to check the shipping costs) and found out that there's a minimum US$ 25 order (100 of those T-filters) and the cheapest shipping method would be US$ 50, so in total US$ 75 for 100 of them. And that's not even including import duty and taxes. I estimate the total would cost me around US$ 94 which is a bit much considering I just need one (plus possibly a couple of extras in case the other filters need replacement some time).
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Re: MegaSTe hardware problems -help locate it please!

Postby dhedberg » Thu Sep 21, 2017 7:03 pm

Fujiyama wrote:
dhedberg wrote:How about Quest Components?

I just registered with them (in order to check the shipping costs) and found out that there's a minimum US$ 25 order (100 of those T-filters) and the cheapest shipping method would be US$ 50, so in total US$ 75 for 100 of them. And that's not even including import duty and taxes. I estimate the total would cost me around US$ 94 which is a bit much considering I just need one (plus possibly a couple of extras in case the other filters need replacement some time).

Ouch! Yes, that's crazy. It'd be cheaper to buy another (non-working) STE and get the parts you need from it.
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Re: MegaSTe hardware problems -help locate it please!

Postby czietz » Thu Sep 21, 2017 8:20 pm

Murata still make comparable EMI filters, part no. DSS1NB32A102.
Maybe you'll be able to find a local electronics distributor that will sell you small quantities at a reasonable price.

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Re: MegaSTe hardware problems -help locate it please!

Postby Fujiyama » Thu Sep 21, 2017 10:07 pm

You're right! I found them at Digikey, and at RS-components as well.
I haven't ordered from either and fear it might become expensive with postage, import duties etc. there as well, but will check into it.

How do you find equivalents for components like this? Is it a matter of knowing your stuff, understanding datasheets and comparing, or are there dedicated websites/databases for this very thing?

Also, are these filters parts that commonly wear down and need replacing (like electrolytic capacitors), or have I just become very unlucky? If the former is true or likely it might be an idea to buy several once I get hold of them, but which ones?
The STe service manual lists several different filters (see image attached) and I assume its similar to what is found in the Mega STe. But it's hard to tell which filters go where. Can you decipher it better perhaps?
ste_noise_filter.png
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Re: MegaSTe hardware problems -help locate it please!

Postby czietz » Fri Sep 22, 2017 6:17 am

Fujiyama wrote:How do you find equivalents for components like this? Is it a matter of knowing your stuff, understanding datasheets and comparing, or are there dedicated websites/databases for this very thing?


In this case I knew beforehand that Murata makes EMI filters so I went to their website to see if they still had any through-hole ones. Note: I didn't compare datasheets between the original TDK and the Murata filter, but slight deviations in e.g. the frequency characteristic won't be problematic anyway.

Fujiyama wrote:Also, are these filters parts that commonly wear down and need replacing (like electrolytic capacitors), or have I just become very unlucky?


Since this is basically a ceramic capacitor with some ferrite beads, I cannot imagine that it would wear down by regular use like electrolytic capacitors. The only EMI filter in an Atari ST that I had to replace had clearly been damaged mechanically. (They are quite brittle.)

Fujiyama wrote:The STe service manual lists several different filters (see image attached) and I assume its similar to what is found in the Mega STe. But it's hard to tell which filters go where. Can you decipher it better perhaps?
ste_noise_filter.png


I think "ALT" in this manual means "alternative", so these are just alternatives (second sources) for identical filters. At least in the Mega STe I currently have on my desk there seems to be only one type of EMI filter.

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Re: MegaSTe hardware problems -help locate it please!

Postby Fujiyama » Fri Sep 22, 2017 10:28 am

I think you're right about "ALT" meaning alternative filters as this doesn't seem to be a critical valued part. According to the list there are 5 options, but the ZJSR5101-102 isn't mentioned. How did you figure out that one?

I should probably take a closer look inside the Mega STe to see if I can find "102" markings on all of them. There are quite a lot of those filters, probably 50 or more, attached to each connector (serial, parallel, MIDI, ACSI etc.). Are they to prevent voltage spikes from coming in and destroying the other components nearby?
I will see if I can order a few from RS-components the next time I create a suitably large order as these big companies commonly have a minimum order and hefty postage costs for just a few items.

Well, my Mega STe joy didn't last long because now I'm having problems with the display output. It's currently connected to an LCD display (in hires mono mode) via a VGA adapter cable and I've started getting an "out of range. 15.8KHz/60Hz" message on the LCD display itself. It often happens if I do a reset (CTRL-ALT-DEL or pressing the reset button) even though the computer has booted fine. Could the monitor be at fault? I do have an Atari SM-144 I could try out again, but the idea was to eventually sell the SM-144 along with the Mega STe and keep the LCD display (NEC Multisync 1990SXi).
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Re: MegaSTe hardware problems -help locate it please!

Postby troed » Fri Sep 22, 2017 1:17 pm

Fujiyama wrote:I've started getting an "out of range. 15.8KHz/60Hz" message on the LCD display itself. It often happens if I do a reset (CTRL-ALT-DEL or pressing the reset button) even though the computer has booted fine. Could the monitor be at fault?


This means your computer has booted in 60Hz low resolution mode. If it's a PAL machine, this indicates a fault early in the boot process (bad TOS, often).

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Re: MegaSTe hardware problems -help locate it please!

Postby Fujiyama » Fri Sep 22, 2017 2:25 pm

Yes, it's a PAL machine.
Perhaps the VGA cable has a bad connection -I'll keep checking.
If it's a TOS issue, shouldn't it happen every time?
Mega STe | MonSTer with dual IDE-CF memory card adapter | STe | SM-144 |NEC Multisync 1990SXi | IDE doubler | ST_ESSC | RSVE | ICD Link II | Link '97 | HD floppy drive/AJAX | HD floppy module | Minolta PCMCIA card-drive | Realtime Clock module | Discovery cartridge | Unitor-2 | Export | Combiner | Steady Eye | Human Touch | Unicorn USB

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Re: MegaSTe hardware problems -help locate it please!

Postby czietz » Fri Sep 22, 2017 3:28 pm

Fujiyama wrote:I think you're right about "ALT" meaning alternative filters as this doesn't seem to be a critical valued part. According to the list there are 5 options, but the ZJSR5101-102 isn't mentioned. How did you figure out that one?


I have a STe service manual (probably downloaded from dev-docs) that mentions the ZJSR5101-102 as one possible alternative:
filter.png


Fujiyama wrote:I should probably take a closer look inside the Mega STe to see if I can find "102" markings on all of them. There are quite a lot of those filters, probably 50 or more, attached to each connector (serial, parallel, MIDI, ACSI etc.). Are they to prevent voltage spikes from coming in and destroying the other components nearby?


While these filters will to some degree also attenuate any incoming spikes, their primary function is EMI compliance, i.e. making sure that no high frequency noise above the regulatory limits comes out of the ports. I suspect Atari wouldn't have gotten the EMC approval otherwise. There's a document from Murata explaining EMI filtering in much more detail: http://datasheet.datasheetarchive.com/o ... 008703.pdf. It even mentions the DSS306-55B 102M filter that is also in Atari's list.
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Re: MegaSTe hardware problems -help locate it please!

Postby Fujiyama » Fri Sep 22, 2017 4:00 pm

So there are multiple versions of the STe service manual! I don't know where I got mine from but will check dev-docs for that same manual which even looks easier to read according to your screenshot.

I would never have guessed that purpose for the filters and will read that Murata document for more info. I suppose not all electronic gear needs to be noise supressed like that, but even DIY projects might benefit from having filters included in their design I guess.

The display sync problem is coming and going so I've used some contact spray on both ends of the cable, the monitor connector and the Atari display socket just in case that was the reason behind it all. These vintage computers are getting a few years worth of mileage behind them and it's probably not uncommon that a lot of problems show up at once. Now if I could only repair everything in one go and continue with a smooth ride from now on :wink:
Mega STe | MonSTer with dual IDE-CF memory card adapter | STe | SM-144 |NEC Multisync 1990SXi | IDE doubler | ST_ESSC | RSVE | ICD Link II | Link '97 | HD floppy drive/AJAX | HD floppy module | Minolta PCMCIA card-drive | Realtime Clock module | Discovery cartridge | Unitor-2 | Export | Combiner | Steady Eye | Human Touch | Unicorn USB

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Re: MegaSTe hardware problems -help locate it please!

Postby siriushardware » Fri Sep 22, 2017 5:17 pm

Well done on finding that faulty filter. I have to admit that's a long way from being the first thing I would have thought about, but your persistence has paid off. At least you don't have to replace the Optocoupler after all.

Fujiyama wrote:
Are they to prevent voltage spikes from coming in and destroying the other components nearby?



Kind of, as symmetrical filters work both ways, they will prevent pulse / RF energy from travelling in either direction through the filter.

In this case their primary function, as mentioned earlier, is to prevent RF energy generated inside the computer from travelling out along the various long cables attached to the machine and being radiated away by them to cause interference to nearby radio receivers. The heavy shielding above and below the motherboard (at least on a Standard ST/e) is also there for that same reason. As the ST's original market was the USA it would have had to comply with fairly stringent FCC laws about keeping radiated interference to a minimum.

Edit: Simultaneous post with czeitz, who said the same thing.

In the UK, the Sinclair Spectrum, BBC model B and other machines made for the UK market at the time operated under no such rules or regulations and both machines are consequently terrible sources of radio interference, especially in the HF (Shortwave) radio bands. When the Spectrum was introduced to the USA (as one of the Timex models) I believe it had to have shielding added before it was allowed to be sold in that market.

But the ST, when it came to the UK, came built just as it had been for the USA market with all the the RF shielding and filtering still in place. The ST is consequently a much 'quieter' machine (in terms of radiated interference) than any of the native British designs.

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Re: MegaSTe hardware problems -help locate it please!

Postby Fujiyama » Sun Sep 24, 2017 2:48 pm

siriushardware wrote:Well done on finding that faulty filter. I have to admit that's a long way from being the first thing I would have thought about, but your persistence has paid off. At least you don't have to replace the Optocoupler after all.


Thanks, but if it hadn't been for your and others' involvement in this thread I don't think I'd come this far so a mighty thanks to everybody for that!
I've definitely learnt a lot through all of this, one of them being that the schematic doesn't always give away all the details, as with the GND connection and 3 pins of the filters (as opposed to 2 pins and not grounding in the schematic).

Regarding the display output sync problems I've been having recently -they've been away for a while though I do get the occasional blue coloured screen (instead of black/white), and wiggling the cable solves it. I suspect it being either bad soldering connections of the 13-pin DIN connector to the motherboard, a worn out 13-pin DIN connector (plugging in the monitor cable appears quite loose) or a bad VGA cable though that part is checked and looks fine.
I'll see how the 13-pin DIN connector looks underneath the motherboard the next time I remove it from the Mega STe casing (probably when I get replacement filters).

Interesting reading from both you and Czietz about the purpose of the filters. A positive side effect for the rest of the world as it was an American computer company behind it!


So what to next? 8O (I've been getting so used to tracing down these problems).
Well, apart from replacing the filter (once I get hold of it further down the line) and checking out the 13-pin DIN socket while at it I'm going to get round to recapping the PSU. Then there's figuring out if I should get a replacement battery for the built-in clock or add a DS-3231 based realtime clock board to the MonSTer board (it uses a more standard and cheaper coin type battery than the Mega STe clock) -I'm still trying to make sense of the Y2K thing and how it all works. The MonSTer board seems to be working as it's supposed to and I've completely replaced the messy old wiring from the board with new wires, neat Dupont connectors and nice/tidy small blobs of hot-glue instead of that nasty bathroom type silicone I used before.
Other than that I think I may actually start using this lovely machine!

.....then there's off to upgrading the STe with a high density floppy drive module, a MonSTer board and other goodies. Tasks I imagine will be much more enjoyable than fixing the Mega STe :)
Mega STe | MonSTer with dual IDE-CF memory card adapter | STe | SM-144 |NEC Multisync 1990SXi | IDE doubler | ST_ESSC | RSVE | ICD Link II | Link '97 | HD floppy drive/AJAX | HD floppy module | Minolta PCMCIA card-drive | Realtime Clock module | Discovery cartridge | Unitor-2 | Export | Combiner | Steady Eye | Human Touch | Unicorn USB

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Re: MegaSTe hardware problems -help locate it please!

Postby Fujiyama » Sun Oct 15, 2017 9:14 pm

A quick note just to say that I've successfully recapped the Mega STe power supply (using Exxos' suggested replacement values) which went fine. I used dummy load resistors to check the output voltages before and after recapping for comparison and to ensure I wouldn't blow up the preacious computer if I had done something wrong with the PSU (which fortunately wasn't the case).
UPDATE: I've just written a "how to" guide on recapping the Mega STe power supply.


I really haven't noticed any difference in performance except that the display quality had gotten better! The display signal appears stronger if I can describe it that way: sharper, the white (monochrome hires mode) now appears more "clean" than the slightly grayer of before and a slight "noise" in the picture appears to be gone. Very nice :D

But now I have some new problems :oops:
I had to desolder and remove a "key" pin (pin 20) of the MonSTer IDE connector (to physically accomodate for a new IDE-CF adapter that I just bought) and now the blitter feature in TOS is greyed out. I suspect it's a bad connection somewhere from those wires going from the various motherboard ICs to the MonSTer connectors (although they do appear fine when I checked) because hot-glueing them didn't last and they got loose and perhaps ripping them ever so slightly loose. I really need a bettery type of glue that keeps sticking while still allowing me to remove such modifications if ever needed.
The blitter works fine when the MonSTer is removed, so at least that's a good sign!

At times like this I really look forward to the day I can just remount the case top and never need to open it again! :lol:
Mega STe | MonSTer with dual IDE-CF memory card adapter | STe | SM-144 |NEC Multisync 1990SXi | IDE doubler | ST_ESSC | RSVE | ICD Link II | Link '97 | HD floppy drive/AJAX | HD floppy module | Minolta PCMCIA card-drive | Realtime Clock module | Discovery cartridge | Unitor-2 | Export | Combiner | Steady Eye | Human Touch | Unicorn USB


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