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Dead 130XE - Any advice?


TroyQ

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Small update:

 

 

Start off with the "troubleshooting" section in the service manual & also download a TTL logic data book. This really helped me fix my 65XE.

 

http://blog.3b2.sk/igi/post/Sams-Computer-Facts-ATARI-130XE.aspx

 

I use the same logic probe for checking stuff quickly but a scope is more ideal ( it's better than nothing I guess ).

 

Also, a logic comparator or EPROM device programmer with TTL logic / RAM test will go a long way. I have an EETools TopMax which is great for checking mask roms / EPROMs , TTL logic and different types of RAM but it's quite expensive. I don't know what I'd do without it.

 

Super big thanks for this link! I didn't see it at first, but I found the logic table for all the ICs in that PDF.

 

I have been busy, so only had a chance to do an initial sanity check of "am I using the logic probe correctly and getting accurate results" Looks like I am.

 

I tested FREDDIE against the Logic Chart in the PDF and had 3 discrepancies: pin 21 should pulse and I get low, pins 34 & 38 should pulse and I get high. Pin 21 is A12, pin38 is R/W and pin 34 goes to pins 3 on DRAM (if I understand the schematic correctly). I know I need to do some more testing, but that to me looks like the issue is memory subsystem related. An address line (A12) is stuck low and the R/W is stuck high (trying to write?). RAM or FREDDIE I am guessing?

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almost all dead 130's I have repaired had bad ram in particular

most non working Ataris had that or MMU problem...

some had bad support chip

rarely did I have a dead Fred..

lastly were the big chips..

 

there was a thread the indicated what was dead based on video color or symptoms at one time not sure if it was here on AA but it was surprisingly good at times... red tint or screen, blue tint or screen, black screen, screen that flashed, garbage on screen (variants of garbage on screen) etc etc...

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I know I need to do some more testing, but that to me looks like the issue is memory subsystem related. An address line (A12) is stuck low and the R/W is stuck high (trying to write?). RAM or FREDDIE I am guessing?

No smoking gun is my take away so far.

FREDDIE appears to be working and stuck trying to

read a lower address. The bar over the top of the

WRT of ram pin 3 indicates a write happens with

negative assertion. /WRT also means this same

thing. /CAS, /RAS as well, both are high until

those signals are brought low to assert them. So R/W

is both a contraction and logical state declaration

which can be taken for just a contraction using

a forward slash by the casual reader. /WR would

be confusing and not nearly as sexy. Hexy?

 

For the moment I would move on to the cheaper or

easier to replace MMU/OS Rom looking for non-

functional chips if one can be found first. No joy

there then socket and replace ram to try again.

A 2nd machine could be testing the ram removed

looking for bad ones. I certainly don't see a

dead FREDDIE if shoestring's post #48 excellent

advice flies in an upright manner.

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  • 4 weeks later...

Its been a bit since I've been able to do any troubleshooting on this but I've finally had the time and I've found a solution:

 

Bad ANTIC chip.

 

Things it was not:

Bad RAM ** (replacing the RAM did not fix the failure, but afterwards, the logic probe produced accurate results on the FREDDIE chip - so it is possible there were also bad RAM)

Bad CPU

Bad GTIA

Bad 10uF or 22uF caps

 

I think I got lucky with my 130XE board in that it was not too much trouble desoldering / adding sockets. By my count, I did 452 pins total and no lifted traces or anything bad. I now have a mostly socketed motherboard. I may still socket the rest of the chips and replace the 4.7uF & 470 uF caps just to satisfy my own OCD-ness.

 

I saw there is another thread for tracking good/bad Mt RAM. I'll put the original ram back in and post the results and pix there.

 

 

Again, thanks to everyone and their advice on this.

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