Dead Falcon

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etomuc
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Dead Falcon

Postby etomuc » Sun Oct 06, 2019 5:37 pm

So, my Falcon seems to be dead. I searched already the forum and the net but I am currently stuck with ideas.

Symptoms:

When I turn on the Falcon, the screen is black. VGA Monitor displays a message that it can't sync this mode. I also checked with Composite Sync, but also no luck. Fan spins, there is a short click in the floppy. Reset seems to reset as the screen removes the message for a second just to display it again. No floppy activities, no beep sound.

Background: I reactivated my Falcon about 2 years ago after being almost 20 years in the cellar. The hard drive was not working, otherwise it worked fine. It had a FX Extender card installed (addon for 8MB of Fast Ram, the usual CPU/Bus-Speed enhancement plus a screen resolution enhancement), so there were a few modifications.

All of a sudden, the screen was black and it didn't work any more. I recognized that one cable for the bus speed enhancement was loose. That's the one, that is attached to the DMA chip (I guess). I resoldered the cable, and everything was fine again. I did then play around with the Falcon, trying to install a CF card and even could get the data and programs from my old drive (it started working again after a few attempts, just to die later forever - but at least I have the data). Then, again, black screen, Again the cable. Again resoldered, but then it did not come back to live. It was dead with the sympoms described above. I wanted to check this in more detail, but didn't have the time, so it ended up again in the cellar - until yesterday.

I spent now the last 2 days with it, first resoldered all cables and made sure the connections really work. I then removed the FXtender card and restored all connections. I again checked that it correctly connects with a multimeter (the only tool I have). Still no luck. I also realized I didn't place the jumper on the expansion bus again, so I did that - and also no change. I am now running out of ideas what it could be...

Ideas are really welcome what I can check next...

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dhedberg
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Re: Dead Falcon

Postby dhedberg » Sun Oct 06, 2019 6:22 pm

Perhaps a long shot, but do you have access to an SM124 or any other Atari monochrome monitor? It could have been a combination of your original problem with the loose cable and that your NVRAM is out of battery, messing up the boot video configuration. Connecting an SM124 forces the Falcon to boot in 640x400 mono regardless of what the NVRAM says.
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Re: Dead Falcon

Postby etomuc » Sun Oct 06, 2019 6:32 pm

I don't have a SM124 but I have a self made monitor adapter which I quickly modified to make the Falcon think a monochrome monitor is attached. Afaik it should still work with a VGA monitor (pin 18+19 to ground).

Unfortunately no difference, still dead.

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Re: Dead Falcon

Postby derkom » Sun Oct 06, 2019 6:37 pm

This is a dumb question, but it's a dumb mistake that I've made before: Do you have RAM in there?

This might be a job for a diagnostic cartridge with a serial connection.

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Re: Dead Falcon

Postby Robson » Sun Oct 06, 2019 7:10 pm

removed
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etomuc
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Re: Dead Falcon

Postby etomuc » Sun Oct 06, 2019 7:32 pm

Yes, 4MB of stock ram. I even tried without ram. There are no stupid questions ;-) It could be something completely obvious that I am just missing.

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Re: Dead Falcon

Postby Robson » Sun Oct 06, 2019 7:39 pm

When removed the Fx card did you put the jumper back on the extension port? Bottom set top row. There should be a jumper on it (top row, 4 pins on the right then jumper - W1 marked on mobo)

Forget it...you answered this question :). Just read it.

I recently had to replace the nvram on mine..so that could be it.
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etomuc
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Re: Dead Falcon

Postby etomuc » Sun Oct 06, 2019 8:14 pm

Regarding the NVRAM I tried to boot in ST mono, which should be possible with the right monitor adapter. I have a custom adapter where I simply grounded pin 18 and 19. If I am not mistaken, that should force the Falcon into ST mono and ignore NVRAM settings. But no difference...

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Re: Dead Falcon

Postby frank.lukas » Sun Oct 06, 2019 8:28 pm

See the NVRam Datasheet -> power the Computer on -> put shortly the Reset Pin at the NVRam Chip on Ground/GND
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Re: Dead Falcon

Postby Latz » Mon Oct 07, 2019 10:38 am

Hi,

IIRC, for FXtender the Falcon clock traces were heavily modified. Check that the "clock separating resistors" R216, R217,
R221 and R222 are restored correct. Also lift and re-seat the chips U62, U63, U67 and U68 to make sure they all have
correct contact. U24 (near midi port) and U52 (right beside fan) were modded, too, right? -->check
If your multimeter supports frequency measurement, you can find the 16MHz at every contact of the resistors above.
With Falcon powered OFF, you should also "beep" (contact test) the clock traces from the above resistors to the
"clock receiving chips".

Latz
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Re: Dead Falcon

Postby joska » Mon Oct 07, 2019 1:21 pm

Yes, check the 500KHz baud-clock to the keyboard- and midi-ACIA (U24 and U52). From my own experience I can say that a missing clock here results in an apparently dead Falcon. I had the exact same symptons as you describe with my first Falcon which had a Speed Resolution card with what turned out to be a broken 500KHz clock.
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Re: Dead Falcon

Postby Bikerbob » Mon Oct 07, 2019 3:50 pm

I have a friend local that has a dead Falcon, is there anyone in NA or EUROPE that does falcon repairs? He has tried lots, it had a mod in it that I think went bad, and he really does not want to mess with it anymore, just wants to get it fixed..

James

etomuc
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Re: Dead Falcon

Postby etomuc » Mon Oct 07, 2019 7:14 pm

Latz wrote:Hi,

IIRC, for FXtender the Falcon clock traces were heavily modified. Check that the "clock separating resistors" R216, R217,
R221 and R222 are restored correct. Also lift and re-seat the chips U62, U63, U67 and U68 to make sure they all have
correct contact. U24 (near midi port) and U52 (right beside fan) were modded, too, right? -->check
If your multimeter supports frequency measurement, you can find the 16MHz at every contact of the resistors above.
With Falcon powered OFF, you should also "beep" (contact test) the clock traces from the above resistors to the
"clock receiving chips".

Latz


3 resistors are removed as there is the clock patch which needs them to be removed. the other one is restored.

I'll check the chips and I also ordered a new multimeter to test the connections... will probably happen next weekend. Thanks

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Re: Dead Falcon

Postby etomuc » Mon Oct 07, 2019 7:16 pm

joska wrote:Yes, check the 500KHz baud-clock to the keyboard- and midi-ACIA (U24 and U52). From my own experience I can say that a missing clock here results in an apparently dead Falcon. I had the exact same symptons as you describe with my first Falcon which had a Speed Resolution card with what turned out to be a broken 500KHz clock.


Interesting... will check that as soon as I have my new multimeter.

What did you do to fix it? replace the crystal?


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