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600XL capacitors


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#76 tf_hh OFFLINE  

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Posted Tue Apr 24, 2018 12:54 PM

Possibly a daft question, but have you isolated whether this is purely a video issue yet? Which is to say, are there any non-visual signs of the 800XL trying to boot? Some months ago, when working on a stock 600XL, I had completely forgotten that the neither luma nor chroma were hooked up to the video jack in the factory, and since I hadn't bothered plugging the audio jack into the TV, for a while I thought the machine was dead. Of course, the 800XL has chroma hooked up, but still, it's sometimes worth hookup up to RespeQt via SIO2PC and checking if there are any signs of the OS trying to boot.

 

Hmmm.... this would be TOO easy :D



#77 flashjazzcat OFFLINE  

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Posted Tue Apr 24, 2018 12:59 PM

Latest fault I discovered and fixed was a faulty delay line (U13) on a 600XL of mine which has been dead for about five years, ever since I did a 64K mod on it. I discovered a broken pin on the OS ROM socket last July while I was live streaming replacement of the RAM sockets on YouTube, but having fixed that and found it still didn't work, I forgot that this was an ideal opportunity to replace every chip on the board for a second time. Anyway: I happened to experimentally pop in a different delay line IC last night and it immediately fixed it. :) So: never say die. :)



#78 Tezz OFFLINE  

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Posted Tue Apr 24, 2018 1:00 PM

You should exchange the PIA for test before you change all these small 74s logic chips. The possibility of a defect PIA is much higher. For example, when PB7 (portbit 7) is defect, the whole OS won´t start with a XL/XE operating system. During coldstart they set PB7 to low (mirror selftest in the memory area $5000-$57FF) and then the OS jumps into the memory detection and zeropage/stack-page test routine. If PB7 can´t set to low by a write access to $D301 in case of a defect, then the CPU jumps to elsewhere and hung up - black screen at all.

 

So go ahead with PIA. Or, if you can, burn a EPROM with a OLD-OS from 400/800 series and plug it in. These OS versions doesn´t toggle PB7 and run also with a defect PIA.

Thanks once again, that's a good point. I'll remove the PIA in the morning and see how that goes. That's really useful regarding the original OS, I'll look at sorting out an EPROM for future diagnostics :)



#79 flashjazzcat OFFLINE  

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Posted Tue Apr 24, 2018 1:01 PM

Is this a good time to plug SysCheck and remind everyone that it's an essential diagnostic tool? :)



#80 Fox-1 / mnx OFFLINE  

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Posted Tue Apr 24, 2018 1:09 PM

Since I already had 3 XL's with a broken delay line...  is there an alternative way to fix this without using the original part?  I ran out of those.



#81 Tezz OFFLINE  

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Posted Wed Apr 25, 2018 6:27 AM

I removed the PIA cleanly this morning and installed a socket. Sadly with the working Hong Kong PIA installed I'm still getting a black screen output. I tested another spare PIA that I have which works fine after testing it in the Hong Kong board so at least that is now another known working IC installed on the board. I haven't yet cleaned up and tested the removed PIA but there is a change through the RF output with both the known working PIAs installed. Instead of the dotted faint white diagonal lines it has a faint vertical white line on the right side border. I'm left now with the remaining few 74LS logic chips to be removed and swapped although I don't have some of the required sockets for those.



#82 Tezz OFFLINE  

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Posted Mon Apr 30, 2018 4:42 AM

I didn't give up with the 800XL repair, with almost everything that I'd removed so far testing bad I think it's safe to asume that perhaps a Commodore PSU was plugged into this system in the past. I'm guessing that was when the keyboard was punched! With that in mind I decided not to mess around and remove every single IC / logic chip from the board. I ordered all the sockets and most of the logic chips from Farnell with the remaining couple needing to be sourced elsewhere. Everything was cleanly removed from the board without any damage, I used hot air after the desoldering gun to be sure. The BASIC-ROM was the only IC that I didn't have a replacement for. With all the sockets installed and the tested ICs / new logic chips installed, I had to borrow CO61618 MMU, CO60472-D line delay and the CA358E rectifier from the Hong Kong board for testing. After double checking everything I powered on and it booted! :) It went straight to self test however as I was expecting it to do so that confirms that the BASIC-ROM was indeed killed too. It was a lot of work bringing this board back from the dead but great to see it live again.

 

I haven't yet tested the original CO60472-D line delay but I'm not too optimistic that has survived. Am I safe to test the original CA358E rectifier in the board? if that original one is bad and not converting AC to DC in that part of the circuit could that possibly cause damage?



#83 flashjazzcat OFFLINE  

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Posted Mon Apr 30, 2018 5:22 AM

The rectifier is on the audio line, so no worries there. Just see if you get sound out of the machine.



#84 Tezz OFFLINE  

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Posted Mon Apr 30, 2018 8:40 AM

The rectifier is on the audio line, so no worries there. Just see if you get sound out of the machine.

Thanks Jon, the original CO60472-D and CA358E tested fine so I'm just missing the MMU and BASIC-ROM now.



#85 flashjazzcat OFFLINE  

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Posted Mon Apr 30, 2018 9:06 AM

Great. Got BASIC ROMs if you need any.

#86 tf_hh OFFLINE  

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Posted Mon Apr 30, 2018 12:51 PM

Since I already had 3 XL's with a broken delay line...  is there an alternative way to fix this without using the original part?  I ran out of those.

 

Hmm. Theoretically it should be possible to replace that IC with an ATMEL ATtiny or PIC micro-CPU. When running at 10 or 20 MHz with internal oscillator, no other external parts should be needed. A SOIC or SOP or TSOP package should fit fine on a DIL-14 adapter PCB.

 

I´m full of projects... maybe anybody else has the time to figure out this... and actually BEST Electronics have them in stock for 5 USD.



#87 Level42 OFFLINE  

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Posted Mon Apr 30, 2018 1:55 PM

A polish site has a solution with a 74LS14 some resistors and some caps. 

 

https://translate.go...t-text=&act=url

 

 

Scroll down to the subject "How dynamic memory works"


Edited by Level42, Mon Apr 30, 2018 2:02 PM.


#88 Fox-1 / mnx OFFLINE  

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Posted Mon Apr 30, 2018 4:31 PM

Thx.  Never came across that site.  Info saved.



#89 Tezz OFFLINE  

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Posted Thu May 10, 2018 6:03 AM

Good to meet you yesterday Jon, I continued with the final jobs on the XLs this morning, the MMU is in place on the board and working fine, I removed the dead BASIC ROM cleanly and installed the precision socket, rev C in place and working fine so that board is now finally 100%. I worked in some contact cleaner on the non responsive keyboard switch on my 600XL to no avail so I removed that and replaced it with the spare so the keyboard is now sorted. The contact cleaner does work if the switch is having a smaller issue, I sorted a few switches on another keyboard so certainly worthwhile giving it a go. The switches that needed replacing were badly corroded with the liquid spills by the former owners.

I'll put my 600XL together today and post some photos :)

Edited by Tezz, Thu May 10, 2018 6:06 AM.


#90 flashjazzcat OFFLINE  

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Posted Thu May 10, 2018 7:27 AM

It was an absolute pleasure meeting and chatting with you yesterday Tezz. Glad the spare parts and ICs helped get another machine up and running. Looking forward to seeing the 600XL. :)



#91 Tezz OFFLINE  

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Posted Thu May 17, 2018 6:33 AM

I was looking at the AWC keyboard switches again this morning, I thought it would be unlikely that any liquid spill could get into the switch itself with the keycaps in place so I took one of the non-functional switches apart and as expected it was pristine inside so it seems it's only the contamination and sometimes later corrosion of the two terminal pins on the base of the switch and/or the PCB through-holes which is eventually breaking electrical contact. If the offending switch is simply desoldered and the pins are cleaned up to remove the contaminants and corrosion (I used high grade wet 'n' dry paper and IPA) along with cleaning the PCB area, the original switch should be able to return back to the board functional again.



#92 ClausB OFFLINE  

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Posted Thu May 17, 2018 7:11 AM

(I used high grade wet 'n' dry paper and IPA)


I prefer a brown ale or a stout, myself.

#93 Tezz OFFLINE  

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Posted Thu May 17, 2018 7:52 AM

I prefer a brown ale or a stout, myself.

:) Sounds good, I can confirm that pale ale is compatible with all Atari models.




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