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Looking for help with my 65XE (boots direct to memory test)


i4000

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Hi all, I am a long-time lurker on the forums but decided to post today for the first time to ask for some advice.

 

I have an issue with a 65XE that I am looking for a bit of advice with. I took my 65XE out of storage earlier this month, powered it on and all was fine, however I quickly noticed that (a) I had no audio and (b) I could not load anything from cassette. After a bit of digging around I found a few posts discussing C19 which is part of both the audio output channel and the SIO audio path. I whipped this out along with the adjacent C20 and tested them in an LCR tester and C19 was dead (complete open circuit, and no capacitance) and C20 was not far behind. So, I ordered a couple of NP electrolytics and replaced both of these.

 

Unfortunately, after setting everything back up, my 65XE will now no longer boot into BASIC, it just boots direct into the memory test, completes the first line of dots (no reds) and then displays a blank green screen. A little bit annoying as, for a change, I had observed all ESD precautions when working on the PCB.

 

I have done a bit of digging and from what I understand, if the machine boots direct into the memory test, then it indicates that a memory error has been detected during initialisation. None of the chips are socketed so I checked all the RAM chips and FREDDIE for dry soldered joints, corrected a few that looked a little 'suspect', but this made no difference. I tried checking for hot chips whilst the computer was powered on and I noticed that if I touch the FREDDIE chip even the slightest amount that the screen corrupts and the computer crashes, in fact it appears that you just need to bring your finger close to it for the screen to start flickering, I am not sure if this is normal. I re-flowed all FREDDIEs pins but no change. Unfortunately, I do not have access to an oscilloscope so cannot start checking signals.

 

I am a little stumped what to do next, ultimately my intention is to upgrade the RAM, I haven't decided yet if this will be a 128KB, 320KB or 1MB expansion via the relevant methods, but I obviously need to get the base RAM working before I start anything. I was just on the verge of ordering a bunch of MT4264-15's, MMU, DIL sockets, and FREDDIE replacement but thought I would check here first before pressing the buy button.

 

What do you guys think? Has anyone come across anything similar before? Am I in the right area?  

Edited by i4000
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2 minutes ago, TGB1718 said:

Do Not Buy MT brand RAM chips, they are the most unreliable RAM chips, look for another brand

Thanks for the advice, any suggestions on reliable brands to go with, or is it just anything except MT?

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In all likelyhood it will, be a DRAM problem. I have been upgrading my collection of 65XE and 130XE recently to 320K using the 800XE320K EMMU GAL from TFHH and some XEs have had similar issues to this. In most cases it was the 4164 DRAM that had failed, mostly Micron Technology, but more recently Samsung, in an 800XLF that I found to have had a fault label I had written about 20 years ago! I have also had 2 out of 6 XEs with faulty Sally CPU's. Apart from that the other big chips have worked solidly. If you have a spare 128K EPROM and programmer, and can replace the OS chip, Shoestring's ROM & RAM tester is quite useful, except it locked up when I had 6 of the 8 DRAM chips faulty in the XLF. Diagnostically, it did prove that I could get a picture. Probably the PBI plug-in board Sys-Check V2.2 XL/XE from TFHH would prove it either way, but if the existing DRAM is MT then good practice is to change it out for a different manufacturer anyway. There is a GAL16V8 JED file for the MMU too from Mathy's web site, but it's unlikely to be the problem. So DRAM and DIL sockets are probably the way forward for now. Incidentally if you purchase 41256 DRAM, these can be substituted for the 4164 for testing purposes, or even permanently if they are a good price, and are also good for the 320K upgrade of course! From what you have said, the 65XE should have the potential of holding 16 DRAM chips.

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On 7/19/2022 at 12:40 PM, i4000 said:

So, I ordered a couple of NP electrolytics and replaced both of these.

Inspect the board to see, if no short between the traces have been made. C49 is just next to the CPU, which can see all the address lines. C50 is also pretty close to important paths. If the Self Test is able to check the first 16KB of RAM and fails then it may look like a kind of problem here. I'd have a closer look. Especially, since just changing the two caps should not cause the RAM to break. And it was OK since it could boot to Basic and you had no problems with the Self Test (except for the sound). 

 

Of course, it still may be a coincidence and memory just broke.

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I have had a good look around the board and cannot find any obvious shorts, solder splashes etc., I don't appear to have a C49 on my board which is a PAL C070067 REV B, from what I can see the board is basically a 130XE with the second bank of RAM and the MMU removed. The current DRAMs are a mixture of MT4164 & Sharp LH2164, from what I can see there has been no re-work on these so I guess it was what was knocking around the factory at the time of production. I have ordered myself up some Samsung DRAM as replacements. I will let you guys know how it goes.

 

Thanks for the help and advice so far :)

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  • 6 months later...

I recently bought a 65XE with the 4 memory chips on Ebay. It has been modified and boots directly to Self test.  When it finishes the memory test, the screen goes crazy with lots of characters and a rapidly rolling screen.  It also has a mod on the BASIC chip and it has a ROM that is different from all of the other ROMs I have seen.  It will boot STAR RAIDERS, POLE POSITION, ATARIWRITER, from a cart. With a BASIC cart inserted, it boots to Self-Test. I have a picture of the BASIC mod.  Is it possible that the BASIC mod is the cause of the problem.

65XE BASIC mod.jpg

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9 hours ago, hueyjones70 said:

I recently bought a 65XE with the 4 memory chips on Ebay. It has been modified and boots directly to Self test.  When it finishes the memory test, the screen goes crazy with lots of characters and a rapidly rolling screen.  It also has a mod on the BASIC chip and it has a ROM that is different from all of the other ROMs I have seen.  It will boot STAR RAIDERS, POLE POSITION, ATARIWRITER, from a cart. With a BASIC cart inserted, it boots to Self-Test. I have a picture of the BASIC mod.  Is it possible that the BASIC mod is the cause of the problem.

65XE BASIC mod.jpg

Atari BASIC chips are normally 24 pin. This 28 pin chip has been hacked into a 24 pin base, presumably to power the chip and to run the address lines to the correct pins. I think it needs to come out.

 

Can you send a complete board picture please?

Edited by TZJB
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3 hours ago, Peri Noid said:

This is a standard factory mod. Nothing unusual.

Thanks, that is good to know. However it looks like they didn't try very hard in the factory.

 

46 minutes ago, _The Doctor__ said:

the orange wire looks pinched and possibly broken

I agree. It's been crushed but looks like it was shorting to the shield.

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make sure no traces on the pcb in the orange wire connection area are nicked or damage about a 1/2 area in total.

once the orange wire is taken care of, meter out the trace and see what driving or support components might have been pulled low.

I'd suspect the usual deoxit scrub down and ROM chip deal from there.

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I found the problem, there was a disconnect between the 25953 and the MMU. I desoldered the socket and there was a badly damaged solder ring so I soldered in a connecting wire and everything worked.  I also pulled the BASIC chip and replaced it with a 24 pin BASIC chip just to improve the appearance.

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