ATARI XEGS Gray screen on boot up

[80sAtariboy]

Can someone please give me pointers on where to troubleshoot please.

My XEGS which I recently purchased boots up to gray screen with a tone that is muffled. It worked fine when I got it and loaded Zybex and then it seems to crash after a while. I switched it off and then on restart this gray screen started. I am using a new USB power source cable, which I use for other 8bits (800xl etc), so I know the electric source is clean. I tried the RF out and its also giving gray screen with tone. 

 

It seems to be stuck in some sort of memory corruption. The chips are not getting hot from what I can feel as I opened the system up. Does anyone think the 6502 CPU has gone? I recently sorted out my XL with a bad CPU as it has a red screen on start up (RAM ICs were ok). Maybe my CPU has gone as the RAM on the XEGS is not showing signs of heating. Perhaps it is the Freddy or GTIA chip?

 

Any advice would be great from the community.  

thanks

[mimo]

Usually CPU or RAM on the XEGS, not unknown to be other issues but they are a good starting point.
@flashjazzcat did a great (as usual) video on this recently 

 

Edited October 15, 2020 by mimo
forgot the link

[80sAtariboy]

@mimo. thanks for the reply and pointer. Appreciated. I will try to replace the CPU first as I have a feeling it is gone. As in the vid - I hope it is not the ROM. 

[+Nezgar]

It could still very likely be the ROM... usually a red or green screen though, not grey. Anyhow - I've seen at least 4 XEGS's revived by replacing that alone in the last couple years on this forum...

 

Unfortunately, all chips are soldered to the motherboard in XEGS's, so replacing any chips will require careful desoldering and replacing with a socket - or just cutting the pins off the original ROM to ease removal of the pins one by one.

 

I can mail you a replacement programmed EPROM and socket - I have the parts onhand. Probably the cheapest thing to replace first. I can also include a 2nd OS EPROM programmed with Shoestring's RAM tester to know for sure your RAM is good too. PM if interested.

 

In the mean time - Since you have a working 800XL, if you want to go through the work/risk of desoldering IC's, you could try swapping them one by one into your 800XL - starting with the CPU as you suspect. Also interchangeable are ANTIC, GTIA, PIA, POKEY - but the ROM and MMU are not.

 

Edit: Hmm, actually an 800XL ROM probably would work in the XEGS for a quick test - you just would have no working BASIC, or Missile Command...

[80sAtariboy]

@Nezgar. Thank you for your post and advice. I have ordered a replacement CPU chip already and will see if that does the trick first. I actually went back and felt if the chips were hot and the CPU is hotter than the RAM and other ICs, so I am hoping this is the fault. 

 

Once I replace this and if there is a problem with the ROM then I will take up your offer. I understand the ROM chips on XEGS are different to XL/XE as I guess they have built in Missile command. 

 

Appreciate your reply. Thanks and will update soon on progress. 

[+selgus]

I have removed many ICs from XEGS motherboards at this point, and I would caution removing something like the SALLY CPU chip before you know you really need to (if you don't have expert skills in desoldering and not messing up PCBs currently). I usually don't worry about lifting pads, because I am just after the chips, but especially on the XEGS', those pads lift quite easily.

 

If you have access to an oscilloscope, then checking some signals on the CPU first, to see if you are getting valid clock signals, or even a multimeter checking VCC and some of the other pins to see if you get meaningful values (using your working ATARI also can help checking what you should expect on many of the pins). You can do this on the DRAM chips too, see if data pins have valid waveforms or you can spot something obvious before possibly risking some of those traces/pads by removing any ICs.

 

Just some thoughts you might consider..

 

B

[Sugarland]

Yes I felt that ordering a replacement CPU was overhasty. You have a working one in your 800XL that can be used to diagnose the XEGS, if the latter can be desoldered. Just because the CPU in the XEGS was quite warm doesn't mean it is not functioning. They get quite warm but not so hot you can't touch them. Yes they do get hot enough that touching one for twenty seconds will be uncomfortable.

Edited October 16, 2020 by Sugarland

[80sAtariboy]

Just to let you all know that I replaced the CPU 14806 and it worked! I had to desolder and then socket the IC, but atleast its working again.

 

Thanks to all for your pointers and advice. 

[TGB1718]

Congratz, nice job not lifting tracks, well done

[+Nezgar]

Awesome! Out of curiosity, it might be interesting to see if by chance the "bad" CPU might happen to still work in your 800XL...

[flashjazzcat]

3 minutes ago, Nezgar said:

Awesome! Out of curiosity, it might be interesting to see if by chance the "bad" CPU might happen to still work in your 800XL...

Worth a try, but I've yet to encounter a CPU which was preventing an Atari from working which turned out to be anything but dead. I wish this were not the case, since I just threw out nine dead 6502Cs the other week after carefully testing each one.

 

The quote marks seem to indicate some scepticism regarding the idea that the original CPU was "bad", even after replacing same took the machine from a non-working state to a working one.

[80sAtariboy]

@TGB1718 Thanks! Yes getting adept at desoldering now. I'm only an amateur who likes to tinker and revive old 8bit computers, working again (Amstrads, Spectrums to Atari's). I grew up with the 400 and 800XL in the UK, so have an affinity for Atari' s, as they are very Americana!  

 

@Nezgar I'm afraid the old CPU was not salvagable, lost a few legs in extraction but I doubt it would have worked. I agree with @flashjazzcat. It's binned now. My 800XL had a red screen fault originally and once I replaced the CPU, it was working. So from that experience when the XEGS went into gray screen fault, I suspected a failure of the CPU from experience. Still do not know why it failed as I know the power supply is a stable USB source. 

 

I have also added heat sinks to the CPU this time, as for some reason the 6502 seems a point of failure. 

 

Thanks again all! Another XEGS lives on! Such a nice design and the pastel buttons are kind of cheerful! 

[+kheller2]

"I have also added heat sinks to the CPU this time, "  Hmm...  smells like a Commodore user.

 

[Sugarland]

Since many A8's have socketed CPU's we're used to a faulty CPU often enough just being corrosion or oxidation on the chip legs, however since the CPU's in the XE's are soldered to the board that means a faulty CPU is more likely just a faulty CPU...