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Troubleshooting a Faulty Atari 65XE


atari65xenajm
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Hello all,

 

I need some help please with an Atari 65XE which I purchased on a trip to Egypt.

 

Here are the symptoms I am facing and I would appreciate any feedback on what to fix (the computer is PAL but the monitor I have can display PAL only in B/W):

 

1- When I power the computer up, I sometimes get the READY prompt, but some other times I get a blank screen on which I have to press the RESET key twice and rapidly for the BASIC ROM to start loading.

2- When BASIC loads, the noisy sound just before the READY prompt shows takes longer than any other 65XE/130XE I have used.

3- I cannot boot to SELF-TEST no matter how hard I tried. The OPTION key works just fine though.

4- When I run SELF-TEST by typing BYE from Atari BASIC, all keyboard keys work as expected, all 4 sound registers work just fine, the two ROM bars are fine. However, instead of seeing two rows and a half worth of RAM, I only see two. The very last RAM block is red.

 

I am sure that the RAM is faulty because I was able to run CPS Salt Diagnostic and it showed me one block as 'F'. I could not run the rest of the tests because the computer just freezes/crashes sporadically. None of the RAM chips (or any other chip for that matter) is hot when touching it.

 

Here are my questions:

 

1- These symptoms are fully reproducible. What is the issue here?

2- Is there any way to map the faulty address to a specific RAM chip? For example can I say that if I have four 16-KB RAM chips thhen the first RAM chip from the top holds the physical address $0000 to $3FFF?

 

Thank you for your help.

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Basic doesn't load, the Rom is present and directly addressable when swapped in.

Strange that startup would be longer. Pretty sure if the powerup Ram test fails it should just go to the Self Test.

 

Ram Test should only show 40 blocks when called from Basic since the Basic Rom overrides the 41-48K Ram area.

Still though you should get 40 green blocks, not 32 with the last one red.

 

The Ram chips - on all except 130XE whether a 2 or 8 chip machine, every chip provides data for every Ram access. On the 130XE the right hand chips are main Ram and act the same. Extended Ram on the left, so same with extended Ram accesses.

 

Possibly your machine has a faulty MMU or some other problem with the memory decode logic.

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Here is one more. I swapped the OS ROM (Arabic v1) with another one I have (Arabic v2), and BASIC now boots faster ((I hope 'boot' is the correct technical term). I can now rule out the speed of booting BASIC (item number 2 above) as a relevant problem.

 

However, this time I wrote a Hello World BASIC program, and noticed everytime I pressed RESET, the whole program disappeared. Since I hear that noisy sound after pressing RESET, I can only think that RESET is causing a Cold Reset every time it is pressed.

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I’d start with taking a very close look at the sockets for all socketed chips. If you have a logic probe, get pinouts for each chip and verify they’re all receiving the correct signals. When one of my 1200XL’s wasn’t going to Self-Test properly, it turned out one socket had a broken wipe so a pin on the 6520 wasn’t making contact.

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Without SysCheck II (which you can't use on a machine like this which lacks an ECI port), isolating the faulty DRAM is going to be a bit trickier. FREDDIE commonly goes bad on these A8s too, and you might get lucky and see some conspicuous rapid evaporation if you spray isopropyl alcohol on the RAM and FREDDIE while the machine is running. If one DRAM dries up fast (i.e. it gets hot): happy days. Replace DRAM and enjoy. Likewise with FREDDIE. The fact the machine is more or less functional suggests to me that replacing one bad DRAM will fix everything.

Edited by flashjazzcat
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which board/ram layout do you have?

also, which rev OS chip?

 

130xe board (2/4 ram chips) - C101700-02c
65xen board (8/16 ram chips) - c101700-001a
65xen board (8/16 ram chips) - c101700-1c

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Without SysCheck II (which you can't use on a machine like this which lacks an ECI port), isolating the faulty DRAM is going to be a bit trickier. FREDDIE commonly goes bad on these A8s too, and you might get lucky and see some conspicuous rapid evaporation if you spray isopropyl alcohol on the RAM and FREDDIE while the machine is running. If one DRAM dries up fast (i.e. it gets hot): happy days. Replace DRAM and enjoy. Likewise with FREDDIE. The fact the machine is more or less functional suggests to me that replacing one bad DRAM will fix everything.

 

Is there a way to know which DRAM by giving the physical address of the fault memory location? $7D3F is shown as a failure from CPS SuperSalt, but no idea which chip that is.

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It is 65XEN with 8 RAM chips (no place for adding 8 more on the motherboard). C100455 Rev 2.

whoops! - my mis-type

both of my 8-chip boards are also 8/8

yours is another OS chip

does SHIFT-HELP change the number keys from numeric to Arabic?

 

you won't identify the actual faulty ram chip without syscheck-II

syscheck-II is hit n miss with the Arabic XE.

the ECI edge connector contacts aren't too great. sometimes if your move/adjust it a little you'll get it to work...other times it'll red-screen.

 

do you have a means to piggyback any ram? if so, that would help you identify the faulty.

Edited by Guest
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whoops! - my mis-type

both of my 8-chip boards are also 8/8

yours is another OS chip

does SHIFT-HELP change the number keys from numeric to Arabic?

 

you won't identify the actual faulty ram chip without syscheck-II

syscheck-II is hit n miss with the Arabic XE.

the ECI edge connector contacts aren't too great. sometimes if your move/adjust it a little you'll get it to work...other times it'll red-screen.

 

do you have a means to piggyback any ram? if so, that would help you identify the faulty.

 

Thanks @brenski. SHIFT+HELP does not change the numbers or lower case. This is Arabic OS ROM v1.

 

I do not have any additional RAM chips unfortunately. May have to purchase one to do a piggyback (pity, there are only 8 easy trials to make). If there is no way to map the physical address to a chip, then I will go ahead and purchase a RAM.

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which of the three is your OS?

 

i've found there are some inconsistencies with the SHIFT-HELP function

 

Works:

130xe board (2/4 ram) - C101700-02c
others do not
65xen board (8/8 ram) - c101700-001a
65xen board (8/8 ram) - c101700-1c
am thinking that the HELP key is is intentionally disabled - as i've tried a known working keyboard
and the neither the SHIFT-HELP works to change number keys to Arabic, nor the HELP key does not exit the self-test screen
Edited by Guest
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Thanks @brenski. SHIFT+HELP does not change the numbers or lower case. This is Arabic OS ROM v1.

 

I do not have any additional RAM chips unfortunately. May have to purchase one to do a piggyback (pity, there are only 8 easy trials to make). If there is no way to map the physical address to a chip, then I will go ahead and purchase a RAM.

 

OK I de-soldered a RAM from another working 130XE computer and piggybacked it on the 65XE RAMs one after the other (power off, piggyback, power on, test, rinse and repeat) and the fault persists. Maybe FREDDIE as @flashjazzcat suggested or MMU as @Rybags suggested?

Edited by atari65xenajm
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which of the three is your OS?

 

i've found there are some inconsistencies with the SHIFT-HELP function

 

Works:

130xe board (2/4 ram) - C101700-02c
others do not
65xen board (8/8 ram) - c101700-001a
65xen board (8/8 ram) - c101700-1c

 

 

Yes I know about this inconsistency. Or, rather, different versions of the Arabic OS ROM. On 65XEN both versions of Arabic OS ROM were common:

 

C101700-001A (1987) is the one that does not have the SHIFT+HELP functionality. The terminal Arabic letters must be forced by pressing Control.

C101700-002C (1988) is the one that does have the SHIFT+HELP functionality. The Arabic font is much better than its predecessor and the OS will force a terminal letter for you if you press the spacebar towards the end of a word (just like any modern computer would).

 

I have edited the post to share the two ROMs I have.

 

post-47812-0-66621500-1519148601_thumb.jpeg

Edited by atari65xenajm
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Is there a way to know which DRAM by giving the physical address of the fault memory location? $7D3F is shown as a failure from CPS SuperSalt, but no idea which chip that is.

 

Each of the 8 DRAMs is responsible for holding one of the bits of the entire range of memory. So - for instance - bit 0 of every memory location may reside on chip 1, bit 1 on chip 2, etc. Of course not every bit in the DRAM need be bad, but a program (like SysCheck's firmware) which identifies which bit in a given memory range does not hold the expected value will be able to suggest which DRAMs are bad.

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Each of the 8 DRAMs is responsible for holding one of the bits of the entire range of memory. So - for instance - bit 0 of every memory location may reside on chip 1, bit 1 on chip 2, etc. Of course not every bit in the DRAM need be bad, but a program (like SysCheck's firmware) which identifies which bit in a given memory range does not hold the expected value will be able to suggest which DRAMs are bad.

 

Thanks for the clarification. Is there a way to troubleshoot FREDDIE vs MMU C061618? Since piggybanking the DRAM did not change the fault signature, these are the only two things left.

 

This thread http://atariage.com/forums/topic/258601-65xe-repair-and-troubleshooting-advice/page-2 mentions it was their MMU, but the OP has an oscilloscpe, and I only have a multimeter handy. I will try to replace the MMU first.

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Is there a way to troubleshoot FREDDIE vs MMU C061618? Since piggybanking the DRAM did not change the fault signature, these are the only two things left.

If the alcohol/heat test doesn't give up any secrets, I go for brute-force chip socketing and replacement, since I have no oscilloscope but am able to remove ICs pretty quickly. Eventually I find the fault. :)

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Basic doesn't load, the Rom is present and directly addressable when swapped in.

Strange that startup would be longer. Pretty sure if the powerup Ram test fails it should just go to the Self Test.

 

Ram Test should only show 40 blocks when called from Basic since the Basic Rom overrides the 41-48K Ram area.

Still though you should get 40 green blocks, not 32 with the last one red.

 

The Ram chips - on all except 130XE whether a 2 or 8 chip machine, every chip provides data for every Ram access. On the 130XE the right hand chips are main Ram and act the same. Extended Ram on the left, so same with extended Ram accesses.

 

Possibly your machine has a faulty MMU or some other problem with the memory decode logic.

 

@Rybags your answer wins! I decided to remove the MMU C061618 from my other machine and piggybacked it on the MMU (since I only have MMU or FREDDIE to play with), and it was the MMU. Now the RESET is a warm-reset. Thank you all for your help and tips!

Edited by atari65xenajm
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