Dead Falcon - no boot / coloured screen only

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Chandler
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Dead Falcon - no boot / coloured screen only

Postby Chandler » Sun Jan 13, 2019 6:29 pm

Trying to diagnose a non working Falcon mobo

It's completely stock and never been modded, it's very clean

So far i have changed TOS rom, new NVRAM fitted and fitted a known working memory card but all i get is this coloured screen pic using an RGB monitor with a VGA to ST adaptor

If i use a high res monitor then the screen is just black

No floppy drive LED

Where to look next?
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Re: Dead Falcon - no boot / coloured screen only

Postby mpattonm » Sun Jan 13, 2019 7:03 pm

Is it consistent, if you reset the machine few times? How is the PSU, does it provide at least 4.9V, stable? What equipment do you have?

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Re: Dead Falcon - no boot / coloured screen only

Postby Chandler » Sun Jan 13, 2019 8:00 pm

Yes screen is same after a few resets

Yes PSU is fine (as used in a working Falcon)

I have no test equipement other than a logic probe (what do i need)

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Re: Dead Falcon - no boot / coloured screen only

Postby christos » Sun Jan 13, 2019 9:32 pm

Ram? Or it could be something with the nvram
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Re: Dead Falcon - no boot / coloured screen only

Postby Chandler » Sun Jan 13, 2019 11:28 pm

I have changed the ram to a known working 4mb factor type

new NVRAM chip works in another Falcon (along with the memory card)

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Re: Dead Falcon - no boot / coloured screen only

Postby Arne » Mon Jan 14, 2019 8:17 am

As usual in case of a dead unit:
  • download the service manual
  • read chapter Troubleshooting a dead unit ch.3.3 in my copy
  • act accordingly
As RAM seems to be completely down a test cart is probably of no use here.
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Re: Dead Falcon - no boot / coloured screen only

Postby mzry » Mon Jan 14, 2019 9:29 am

Your problem seems very similar to this guys Falcon too:
https://www.exxoshost.co.uk/forum/viewt ... =23&t=1446
Perhaps you could work together to fix them both.
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Re: Dead Falcon - no boot / coloured screen only

Postby calimero » Mon Jan 14, 2019 5:08 pm

mzry wrote:Your problem seems very similar to this guys Falcon too:
https://www.exxoshost.co.uk/forum/viewt ... =23&t=1446
Perhaps you could work together to fix them both.

If you remove RAM board completly, do you get same patern on screen.
I ask this because guy on exxos forum wrote:

"I removed the 4Mo Memory = same"

how can you get anything on screen if there is no RAM?!
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Greenious
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Re: Dead Falcon - no boot / coloured screen only

Postby Greenious » Mon Jan 14, 2019 8:13 pm

mzry wrote:Your problem seems very similar to this guys Falcon too:
https://www.exxoshost.co.uk/forum/viewt ... =23&t=1446
Perhaps you could work together to fix them both.


That guy gave up and sold it on ebay last month...

Chandler... did you buy this? :D

Anyway, the servicemanual suggest checking on the 32MHz oscillator that provides the system clock.

Oh, if you haven't already, make sure to reseat all those GALs on the mobo.
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viewtopic.php?t=5040

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Re: Dead Falcon - no boot / coloured screen only

Postby Greenious » Mon Jan 14, 2019 8:23 pm

calimero wrote:how can you get anything on screen if there is no RAM?!


Oh, technically speaking, you always get something on the screen if the video circuit is working. Even though it is completely black or white.

The image is however not consistent with a working ram controller/circuit. The databus got pull-up resistors, and should read all 1's (or $ffffffffff.....) if the ram is removed, and something more random with ram plugged in if ram was working.

anyway... this suggests, after screening through the f030 service manual, that either the master clock (32MHz oscillator) is broken, or the COMBO IC. :coffe:

Swapping the oscillator is definately the easiest and cheapest option at this point, since you have no oscilloscope or frequency meter available to actually check it.
Updated my guides as of june 28th, 2016. Check'em out and feedback!
viewtopic.php?t=5040

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Re: Dead Falcon - no boot / coloured screen only

Postby Chandler » Tue Jan 15, 2019 11:57 am

Which Oscillator is the master clock? there are 2 oscillators on the board

1 in the middle next to the large capacitor and the other next to the DSP chip

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Re: Dead Falcon - no boot / coloured screen only

Postby Greenious » Tue Jan 15, 2019 2:27 pm

It would be the 4 pin oscillator that has 32.000Mhz stamped on it, U37, right hand side, under the floppy, next to the DSP.
Updated my guides as of june 28th, 2016. Check'em out and feedback!
viewtopic.php?t=5040

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Re: Dead Falcon - no boot / coloured screen only

Postby mpattonm » Tue Jan 15, 2019 9:17 pm

The one next to the DSP chip with 32.000MHz printed on it is - for DSP. Its not the main clock. System bus clock is all the way down, left to the cooler. Its either DIP14/DIP8 package crystal generator, or (in case of Falcon equipped with TV modulator) two pin quartz crystal in HC49U package. In any case, its rather printed with 32.08498MHz (for PAL machine).
The former one is often failing, but without oscilloscope you will hardly find its really failing part. In any case, for the sake of simplicity, it can be replaced with generic 32.000MHz part, your Falcon would boot with it and you would only loose RGB output and of ability to run most demos.

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Re: Dead Falcon - no boot / coloured screen only

Postby mpattonm » Tue Jan 15, 2019 9:33 pm

Take a look here: http://www.atari-wiki.com/images/b/b3/F ... EC_skt.jpg
System bus clock is either on U65 position, left to the Dallas chip, like in this case - or it would be on Y3, right next to the cooler.


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