Mega STE that works in high resolution but not in low

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Mega STE that works in high resolution but not in low

Postby zapp_man » Sat Apr 11, 2009 9:39 am

Hello All great to see other people still using one of my favourite machines, anyway back to the question.

I have a Atari Mega STE that works when in high resolution but not in low resolution

High resolution with SM144 works great full desktop can turn blitter on and off(will start to boot automation disk telling me I don't have a virus then stops loading and goes back to desktop, I guess because it likes low resolution?)

Low resolution with CM8833-II boots past white screen then stops at black/grey there is drive activity and keyboard clicks it is my pride and joy (could never afford a falcon, wanted to get myself a Satandisk for it)

Low resolution with a TV CRT managed to get it to stop tuning for a few seconds but similar scenario but I cant check to see if there is a white screen before the black screen appears(but there seems to be waves moving up the screen.

Tried popping memory, even booting without it stayed at the white screen with no sound!
Any help would be great, thanks in advance :)
Mike
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Re: Mega STE that works in high resolution but not in low

Postby nativ » Sat Apr 11, 2009 12:43 pm

Hello,

It is very likely that an Automation disk will refuse to run in High Resolution.

It's also very possible that the Automation disk doen't like Mega Ste's aswell, and therefore will refuse to boot in Low/Medium or High resolution.

Have you tried booting into Low resolution with no disk in drive A:/ ?

Everything sounds in order for you booting in Hi res.

Can you read disks when using High resolution? Just to demonstrate that the disk is not corrupt and the floppy drive works.

Have you given it long enough to load desktop?
Have you any known blank disks that you can pop in Drive A:/ to speed up the boot?


That ought to narrow things down.

Thanks

Ashley
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Re: Mega STE that works in high resolution but not in low

Postby Frank B » Sat Apr 11, 2009 9:11 pm

nativ wrote:Hello,

It is very likely that an Automation disk will refuse to run in High Resolution.

It's also very possible that the Automation disk doen't like Mega Ste's aswell, and therefore will refuse to boot in Low/Medium or High resolution.

Have you tried booting into Low resolution with no disk in drive A:/ ?

Everything sounds in order for you booting in Hi res.

Can you read disks when using High resolution? Just to demonstrate that the disk is not corrupt and the floppy drive works.

Have you given it long enough to load desktop?
Have you any known blank disks that you can pop in Drive A:/ to speed up the boot?


That ought to narrow things down.

Thanks

Ashley



Mine had the same symptoms but Simbo fixed it for me. One of the chips had died.I don't know which one but it was a common part. Simbo will know the part number :)
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Re: Mega STE that works in high resolution but not in low

Postby nativ » Sat Apr 11, 2009 9:57 pm

That's it,

If none of the above can route out a simple soloution, then it's on to the hardware!

CheeriO
Atari STFM 512 / STe 4MB / Mega ST+DSP / Falcon 4MB 16Mhz 68882 - DVD/CDRW/ZIP/DAT - FDI / Jaguar / Lynx 1&2 / 7800 / 2600 / XE 130+SD Card // Sega Dreamcast / Mega2+CD2 // Apple G4

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Re: Mega STE that works in high resolution but not in low

Postby zapp_man » Sun Apr 12, 2009 7:45 am

Hello all, the machine seems to operate quite nicely in high resolutuion the desktop does take that bit extra time to display itself without a floppy in the drive but that is quite normal (I have most of my software in storage at the moment, so it is difficult to test the floppy drive fully but I have tested the same Automation floppy on another ST connected to my Phillips CM8833-II and it worked like a charm. I will try and find an application that will run in high resolution.
Thanks
Mike
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Re: Mega STE that works in high resolution but not in low

Postby simbo » Mon Apr 20, 2009 1:23 am

viewtopic.php?f=15&t=13493&st=0&sk=t&sd=a&start=15

if you look here youll see u504 just to the right of the psu and in the middle of a group of 4ic's in the center of the board

u504 is a selector chip its a 74S257 i used an LS type {same chip just a low power version}
in frank_b's mega STE you'll get one from RS components
you can use as this machine does the F version or the HCT version but not the HC version

to replace it its best to simply cut all its pins then remove each pin first using a soldering iron
then clean the holes out using a desolder pump or some desolder wick

and resolder the new one

youll find if you disconnect pin 7 of this IC you can boot into colour mode again
however mono mode will fail instead this is a good way to confirm the fault without getting a chip first
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Re: Mega STE that works in high resolution but not in low

Postby Shredder11 » Sun Aug 28, 2011 10:36 pm

Just plugged in my newly acquired Mega STE that I received last Wednesday, and it works fine apart from the colour modes being in black and white, and the floppy not being able to read or write without an error box appearing. The computer seems to function fine despite the screen being very dark in the colour modes. By the way the original Atari mouse feels like brand new, and is actually very enjoyable to use!
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Re: Mega STE that works in high resolution but not in low

Postby qq1975b » Wed May 16, 2012 10:11 am

Hi @Shredder11,
thank you for your reply on my "Atari Mega STE boots only in monochrome" thread.
As I said, my MSTe doesn't show anything in a TV (SCART Cable). Only works Ok in monochrome with the SM146 monitor. But, I have an Amiga 2000 that has the same problem as your Atari. Shows identical image on LED TV (on a CRT only shows image, but correctly, for less than 1 sec.). I connected it to the 1084S monitor and then it worked ok. In the forum, they told me that it would possibly be the FastBlanking that is missing (scart cable- PIN 16 has to have 1-3 volt signal) or the display output doesn't work well (5V from one specific pin) that I think that it is my problem :( . Maybe you have to try the RF cable too to be sure that the problem is from the faulty chip...

Hope that this helps!
Trying to learn...
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Re: Mega STE that works in high resolution but not in low

Postby Shredder11 » Wed May 16, 2012 10:41 am

The SCART cable I use is a known working one with my other Atari STE machines; I need to try snipping the leg of the chip mentioned here to see if the colour mode is working or not. The chip is just a bit of logic to act as a switch I think. My Mega STE was originally a French model, to which I converted the TOS and keyboard to UK. Being a French model means it does not have a modulator inside and no RF port on the back.

As for the SCART pin 16 you mention, my Amstrad CPC and Sinclair ZX Spectrum 128K +3 both display the same video output as my Mega STE. I tried applying voltage across the pin with a battery, and this was using a Philips CRT TV but the result was the same. The Spectrum has a RF port and that displays correctly on the same TV.
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