520ST floppy drive problem

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dentman42
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520ST floppy drive problem

Post by dentman42 »

Back in February, I got an 520ST (NTSC-US, I'm located in the States) system via eBay consisting of a 520ST (no RF, no internal floppy, box and sticker on bottom of computer say Rev A, motherboard says Rev B), SC1224, SF314 and SF354. All with boxes and possibly all packing materials, but the only manual is for the 354. It was all supposedly working. When I hooked it up, all I got was a black screen. The monitor got high voltage and when powered off, showed the normal raster collapse. The power light on the computer lit. When I disconnected power, the light on the disk drives blinked. When powered up with floppy connected, there was no activity on the drive. So I figured (correctly as it turned out) bad motherboard.

Last night, I received another 520ST (also marked Rev A on the computer and Rev B on the board) supposedly working (computer only w/o mouse or ps, and messed up keyboard, but all I needed was a good motherboard). Hooked it up and got 2 bombs. Looked up 2 bombs, tried again and got 4 bombs. Not really wanting to do the x inch drop trick (I've seen it listed as 3 inch, 4 inch, and 5 inch) I opened it and pressed on all the socketed chips. Powered it on, got GEM. Hooked up the 314 and powered on. Light came on, motor ran, and after 30 seconds or so I got GEM. Popped in a disk, went to format but it was grayed out. Clicked on Floppy Disk A, took the unreadable error, cancelled, and format was available. Gave it a name, left the single-sided default, and clicked format. The head stepped very slowly for 5 or 6 clicks, then it errored out. Tried another disk, same thing. Tried the 354, same results. So I opened up the 354 and watched it. When the head steps, it steps forward and immediately jerks back. I tried powering off the drive, turning the head stepper motor by hand to move the heads toward the middle of the disk (and verify that it wasn't seized up). It moved smoothly. I powered back on and it stepped back to the outside, and again when it was supposed to step during the format, it stepped and immediately jumped back. I have not opened the 314 to watch but I expect the same behaviour.

Is this a known type of problem? (I didn't find anything this specific when I searched.)

Were these drives unreliable enough that both could have failed in the same way? Am I more likely looking at a failed disk controller chip? (Of course, it's soldered in on both boards)
I looked for a 74xx06, 74xx14 or 74xx16 but didn't see one (it was late, I could have just missed it). I have a stock of either '06 or '16 chips and sockets, so except for the removal part, that shouldn't be too painful to replace if it's the fault. (I wouldn't expect them to connect a WD controller directly to the drive but just because I've always seen it buffered on other systems doesn't mean it's not unbuffered here).

I'll try a PC drive (or even an Amiga drive mech) this weekend. I have several PC 1.44 drives that support double density and have drive select jumpers (I've used them successfully on TRS-80 and Amiga except Amiga didn't see disk change). I'll try connecting them to the interface board from one of the Atari drives this weekend. I'll also try writing an ST disk from a PC, but I expect to have the same step issue when reading a disk.

Also, I got brave (or stupid) and decided to do some chip swapping to see if I could get the other ST board working. One at a time I swapped all of the socketed chips from the bad motherboard into the good (except maybe for disk I/O) board. The two square chips were bad (with either one or both in the new board, I got the black screen of death). All of the other chips appear to be working fine (the working board still works, the floppy problem persists). So then I put the good square chips (GLUE and MMU?) in the bad board and powered up. This time the screen lit up and I got a garbage pattern that looked like what I get on the good board for a split second after power up before it clears to a white screen but the bad board just hangs at that point. Reset just brings up the same screen. The pattern reminds me of bad RAM on an 8-bit machine (at least TRS-80 or Apple - I haven't had bad RAM in an Atari or Commodore).

(I'll take pictures of these boards if they're wanted for the archives.)

(If anybody is interested, I have a decent collection of 8 and 16 bit systems including TRS-80 Model I, Model III, Model 4, Model 4P, CoCo 1, CoCo 2, CoCo 3 and MC-10, Atari 400, 800, 800xl, 1200xl with bad keyboard, and dead 600xl, C64 and 128, Apple ][+, //e, //c and iigs, Timex Sinclair 1000 [US marketed rebadge of ZX81], Amiga 1000, 500, 2000 and of couse the STs. Also some older MACs because they were cheap. I grew up on TRS-80 Model I and Color Computer, didn't have the money for additional platforms at the time but had friends with Atari, C64, Apple and TI.)
Last edited by dentman42 on Fri Sep 25, 2009 2:15 am, edited 1 time in total.
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Re: 512ST floppy drive problem

Post by spiny »

dentman42 wrote:
Were these drives unreliable enough that both could have failed in the same way?
no, they are just really old now.

a pc floppy should do the trick like you suggest.
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Re: 520ST floppy drive problem

Post by insanity »

dentman42,

any chance of you taking some photos of the motherboards for our wiki?

http://www.atari-forum.com/wiki/index.p ... _revisions

Thanks

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Re: 520ST floppy drive problem

Post by wongck »

Blank white screen sounds like ram issue.
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dentman42
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Re: 520ST floppy drive problem

Post by dentman42 »

@insanity: Yeah, I can take some pictures. Both machines seem to be the same rev motherboard. The one that doesn't work has one additional chip socketed vs. the working one but otherwise I think they're identical.

@wongck: The bad one doesn't get to a blank white screen. With its original bad chips, it's a black screen, no indication from the monitor that the computer is there exept for the slight pop from the speaker when the computer is powered on or off. When I put the good chips from the working board in the bad board, it gets the garbage pattern (presumably random data in video memory), but never wipes to the white screen that precedes GEM. As I said, it looks like bad RAM on an 8-bit system. I'm a bit iffy about desoldering 16 RAM chips (this board is 41256 DIP package), but I have a friend who has much better soldering/desoldring skills than me. If we get bored it may get done, but I still need to replace the other 2 chips (a shame, because I have a bunch of old XT and AT mobos loaded with 4164, 4464, 41256 and 44256 chips - have some on old VGA cards too). As it is, the motherboard I just received is working except for the floppy drive issue and I'm hoping the problem is with the drive mechs rather than the motherboard. It would be so much easier to troubleshoot the bad board if they'd just socketed the RAM...
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Re: 520ST floppy drive problem

Post by wongck »

dentman42 wrote:As it is, the motherboard I just received is working except for the floppy drive issue and I'm hoping the problem is with the drive mechs rather than the motherboard. It would be so much easier to troubleshoot the bad board if they'd just socketed the RAM...
I have seen several ST mobo and in all those cases, the memory is soldered in.
For my 520STFM, I was able to just solder additional ram into the missing slots and get it to 1MB.
On another 520ST, with a different mobo version, that cannot be done.
Sure swapping the FDD is far easier. :lol:
My Stuff: FB/Falcon CT63 CTPCI ATI RTL8139 USB 512MB 30GB HDD CF HxC_SD/ TT030 68882 4+32MB 520MB Nova/ 520STFM 4MB Tos206 SCSI
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dentman42
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Re: 520ST floppy drive problem

Post by dentman42 »

Well, I managed to get it working using an Epson 1.44 meg PC drive with a drive select jumper to make things easier

At first, it still failed. I formatted a disk on the PC and the ST could read it. I bulk erased the disk and the ST finally formatted it.

I tried the original mechs again. Nothing from the 354 but the 314 read it. Writing/formatting on the 314 alternated between a write protect error and a "disk is unusable" error, so maybe it's just a bad write protect sensor (epson mech - were these optical or mechanical WP sensors?).

I wrote a few images out on the PC using Floppy Image v 0.94 and got to play Marble Madness, Star Raiders and Alien Syndrome so it looks like I finally have a working ST system. Now if I can just find a drive that fits the case better. I can extend the power cable, but having the data connector on the wrong side of the drive makes things tough...

I'll try to get some motherboard pics up later today.

(edit - Now that I think about it, I suppose the apparent stepping problem I saw was actually a re-seek attempting to find a usable track 0 rather than a stepper problem. I wish ST stuff was as "easy" to obtain as Amiga stuff here in the States. I'll have to take an Amiga floppy drive apart and see if the connections line up. If so, I could get hold of a couple more 1010s and use them to rebuild the Atari drives.)
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Re: 520ST floppy drive problem

Post by wongck »

My replacement FDD on my ST520 is a Teac FD-235HF.
Works great as well :mrgreen:
My Stuff: FB/Falcon CT63 CTPCI ATI RTL8139 USB 512MB 30GB HDD CF HxC_SD/ TT030 68882 4+32MB 520MB Nova/ 520STFM 4MB Tos206 SCSI
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yerzmyey
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Re: 520ST floppy drive problem

Post by yerzmyey »

By the way,
is that true that original 520 ST cannot handle 720Kb disks?
I mean - as far as I know there are two diskdrives for 520 ST:

Image
SF314

and

Image
SF354.


I hope one of them can handle 720Kb diskettes?
http://ym-digital.i-demo.pl/ ATARI 520ST music-band
http://ay-riders.speccy.cz/ ZX Spectrum music-band
http://yerzmyey.i-demo.pl/ ZX/A500/A1200/ST/XL music
https://soundcloud.com/yerzmyey ZX/A500/A1200/ST/STE/F030 music
http://z80.i-demo.pl/ MP3 archive of Z80 chip music
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Re: 520ST floppy drive problem

Post by spiny »

yerzmyey wrote:By the way,
is that true that original 520 ST cannot handle 720Kb disks?
I mean - as far as I know there are two diskdrives for 520 ST:

Image
SF314

and

Image
SF354.


I hope one of them can handle 720Kb diskettes?

yes, it's true.

early ST drives were single sided only, so could not 'see' double sided disks.
single sided drives had the 'big eject button' as opposed to the later double sided drives which has the more 'pc like' small eject button.
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yerzmyey
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Re: 520ST floppy drive problem

Post by yerzmyey »

Many thanx for Your reply.
So it's only a question of diskdrive, not any TOS-related problems.
It's very good.
Well, maybe one day I'll get the real ST with SF314 into my dirty hands. :) :) :)
Greetz!
http://ym-digital.i-demo.pl/ ATARI 520ST music-band
http://ay-riders.speccy.cz/ ZX Spectrum music-band
http://yerzmyey.i-demo.pl/ ZX/A500/A1200/ST/XL music
https://soundcloud.com/yerzmyey ZX/A500/A1200/ST/STE/F030 music
http://z80.i-demo.pl/ MP3 archive of Z80 chip music
No good deed will escape unpunished.
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