Dead Falcon - no boot / coloured screen only

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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 stormy » 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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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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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.
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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.
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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 32.084988MHz (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.
Last edited by mpattonm on Mon Feb 11, 2019 8:51 pm, edited 1 time in total.

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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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Re: Dead Falcon - no boot / coloured screen only

Postby Chandler » Thu Jan 17, 2019 9:39 pm

OK on my mobo it's a 2 pin package on Y3

Any idea where i can get some of these? i'd rather get the exact part: 32.08498MHz

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Re: Dead Falcon - no boot / coloured screen only

Postby mpattonm » Fri Jan 18, 2019 7:30 am

Thats a tough one: the only place I know of is http://www.best-electronics-ca.com/custom-i.htm
In the end it might be considerably easier for you to gain an access to oscilloscope and check the current component first.
In my opinion, based on first picture, CPU is at least partially working and getting clock signal. But of course I might be wrong.
I would also suggest you to get/borrow a diagnostic cartridge, it could give you some more information on what exactly is wrong with unit.
Last edited by mpattonm on Fri Jan 18, 2019 12:56 pm, edited 1 time in total.

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Re: Dead Falcon - no boot / coloured screen only

Postby joska » Fri Jan 18, 2019 8:31 am

mpattonm wrote: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.


Or lift the right side (the one pointing towards the fan) of L102, and connect the DSP-clock to the lifted side of it.
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Re: Dead Falcon - no boot / coloured screen only

Postby fidzen » Fri Jan 18, 2019 6:46 pm

I had similar problems with one of my Falcons. I had some coloured pixels on black screen when booting.
I turned out to be the Combo IC. I bought it from Best Electronics.
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Re: Dead Falcon - no boot / coloured screen only

Postby Chandler » Fri Jan 18, 2019 6:54 pm

Can anyone advise a basic scope for testing things like this? will a cheap LCD type do it?

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Re: Dead Falcon - no boot / coloured screen only

Postby dhedberg » Tue Jan 29, 2019 11:50 pm

If you need any Falcon030 custom chips, I have most of them. Just send me a PM.
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Re: Dead Falcon - no boot / coloured screen only

Postby Chandler » Wed Jan 30, 2019 9:57 am

Regarding the 32.08498MHz crystal

I have since found out it is also used in the PAL STE and Mega STE

Well there is a 2 pin crystal in the same package with the same number on it to the left of the motherboard

So, would this work in the Falcon?

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Re: Dead Falcon - no boot / coloured screen only

Postby Greenious » Wed Jan 30, 2019 1:22 pm

Chandler wrote:Can anyone advise a basic scope for testing things like this? will a cheap LCD type do it?


Yes, the key parameter is the sample frequency. You need a sample frequency of 70Mhz, to verify frequencies up to 35MHz.

Many cheap scopes have a total samplng freq of 100 millon samples per second, which is divided among the channels, as long as it can 'focus' on 1 channel alone, you are good.
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Re: Dead Falcon - no boot / coloured screen only

Postby Rustynutt » Wed Jan 30, 2019 8:51 pm

Did you look at the clock buffer, if present?
NTSC Falcons have the 4 pin can to the right of the NVRAM, PAL has a 2 input, forget where.
Last edited by Rustynutt on Wed Jan 30, 2019 8:55 pm, edited 1 time in total.

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Re: Dead Falcon - no boot / coloured screen only

Postby Rustynutt » Wed Jan 30, 2019 8:53 pm

The FPU and SDMA share the same clock line. Oversight in design :(

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Re: Dead Falcon - no boot / coloured screen only

Postby Chandler » Sat Feb 02, 2019 12:09 pm

I do want to change the Y3 crystal on the Falcon

it's a 32.08498MHz

I have since found out it is also used in the PAL STE and Mega STE

Well there is a 2 pin crystal in the same package with the same number on it to the left of the STE motherboard, different Atari part number but identical crystal number - 32.08498MHz

So, would this work in the Falcon?

If so i can "borrow" one from an STE to test


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