Help troubleshooting Atari 1040STf

[abar1120]

    Hello All,

 

I"m came across an Atari 1040STf and have since been trying to get the system working.  This is a North America model and I've yet to get any video output from the device.  I do not have an Atari ST Monitor.  Instead I've attempted to use VGA cables purchased from ebay.  I have 3 dell monitors including one that is supposedly compatible.  I have a monochrome cable and a color one as well.  I've also attempted to connect the unit to scart upscaler with another cable I've purchased.   The unit turns on but I get little indication it's working as intended.  I always see no signal when using the scart cable.  From time to time I see the no signal found message dissappear to present just a black screen when using the VGA cables.   I believe the power supply is healthy as the unit's power LED is turning on and I have verified both rails have the correct voltage (5v and 12v).    This is intermittent however at times I'll get signal (but just black screen) and other times I see the "signal not detected" message on my monitors.  For the most part the Floppy drive always make noise if booted with a disc inside but sounds unhealthy.  I've re-seated all the removable chips.  Can other North American ST users tell me how they get video to output on their respective systems when an ST monitor is not available?  I want to make sure the methods I'm using will work.  Does anyone out there have any suggestions for the next step in troubleshooting ?  I'm willing to try just about anything.   Maybe someone else has had this problem.   I also want to note that this model does not have the ability to connect via RF as the modulator is absent.  It's my understanding this was removed from the STf models and is present on the STfm models.  Any help is greatly appreciated.

 

[ParanoidLittleMan]

It seems that something is broken, and it can not produce valid video signal. How long that STf was out of use (unpowered) ?

 

[abar1120]

I have no way of telling how long it was out of use.  I purchased the unit 4 months ago at a yard sale.  It may have been sitting around for years.

[Zogging Hell]

I don't know whether your VGA cable has an audio out? If it does and you press a key and get a beep (keyboard click) or repeated beeps if you hold down the key the ST is probably ok, but the cable might be a problem.

 

The disk drive is quite likely to be faulty at this point. You could try using a floppy disk cleaner to try and clean the heads, or do it yourself if you are happy to open the drive and clean the heads with isopropyl and a q-tip or similar.

[abar1120]

  My VGA cables have audio connectors and I have plugged them into speakers and held keys down.  Unfortunately no beeps at all.  Are there any chips on the board I can scrutinize?  Another possibility is that chips have been removed in the past and reinserted incorrectly.  I can’t seem to find a picture of my specific board online.  If anyone is interested I’d be glad to take pics of the board and post them just to be sure everything is oriented correctly.    

[ParanoidLittleMan]

If this was not used over many years capacitors in power supply may be in very bad shape, so bad that normal work is not possible. Even if voltages are OK, filtering of them may be very bad. Oscilloscope check would be better.

In any case, because age of machine so called recapping (replacing electrolyte capacitors) is necessary - for reliable work.

There are service manuals of diverse Atari versions online with schematics and mainboard layouts, so can check components.

https://docs.dev-docs.org/

 

[Zogging Hell]

There is a list and photos of a lot (all maybe?) of the motherboard revisions here.

 

http://www.atari-wiki.com/index.php/Atari_ST_motherboard_revisions

 

A diagnostic cartridge might also be a good idea, once you have recapped the PSU (or replaced) as Paranoid suggested.