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Post by svart on Jan 4, 2016 9:03:28 GMT -6
So one of my holiday projects was buying a cheap broken PCM80 and fixing it..
What a pain in the ass those things are.. Big old through-hole chips.. UGGH.
Old school digital design, no planes, tiny thin traces, longitudinal/horizontal trace layout.. DOUBLE UGGH.
Literally no decoupling on the board.. TRIPLE UGGH.
Leaking old pcb filled caps eating up the board. QUAD UGGH.
Anyway, the first problem was no LCD. Typical PCM80 problem where the main bulk cap had leaked and eaten most of the traces away around it. I stripped the parts and scrubbed the PCB until the copper was clean, then rebuilt the traces with wires and put the parts back on.
Display fixed, but now I got 3 errors, E7, E8, E9 which were memory problems.
Tracing the problem was almost impossible, since I have no way of knowing the init and memory testing routines of the design.
I literally had to order a handful of different 74 series logic chips and hope that replacing them worked.
So it turns out that two chips caused the problems, and replacing them allowed the unit to boot.
Now I just need to hook it up and test it out to see if audio works.
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Post by rocinante on Jan 4, 2016 9:45:01 GMT -6
Well dude my hat goes off to you cause I would never even begin to think I could pull that off.
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Post by Ward on Jan 4, 2016 9:58:05 GMT -6
At least there was no Quintuple UGGH... you might have gone all postal on us!
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Post by svart on Jan 4, 2016 9:59:19 GMT -6
Well dude my hat goes off to you cause I would never even begin to think I could pull that off. Debugging old tech like this is hard because there isn't much precedent for how things were done even just 20 years ago. Each design could be vastly different from the next, even from the same manufacturer because mass production of electronics was still an arduous job done mostly by hand, so there was little, to no reason for manufacturers to push for and adopt cutting edge technology. Nowadays, there is a lot more conformity on hardware and software design, and with the proliferation of the internet, a lot more people have access to knowledge of the *right* way to do things. Manufacturing is mostly machine based now, so design practice centers around a "design for manufacture" process, which further whittles away some types of design practices. There are still some holdouts who cherish the idea of older being better, but progress always marches forward, without them. Luckily, Lexicon had an extensive self-testing method in their software upon bootup, which gave me the error codes, which were also very luckily spelled out in the service manual. That's one thing that manufacturers do not do anymore, and that's publish extensive service manuals. Partly because better design practices have greatly reduced the field failures, and partly because boards have become so integrated that debug requires expensive equipment that repair shops just don't have, and finally, that the new design/manufacture processes have made boards so cheap, that it's often more cost effective to simply swap boards than to pay a tech to troubleshoot for hours. |
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Post by svart on Jan 4, 2016 10:00:31 GMT -6
At least there was no Quintuple UGGH... you might have gone all postal on us! I think the quintuple UGGH was where the through-hole legs were all bent over flat against the PCB. During desoldering, I had to straighten each leg so it would pull through without destroying the hole. |
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Post by rocinante on Jan 4, 2016 10:06:00 GMT -6
At least there was no Quintuple UGGH... you might have gone all postal on us! I think the quintuple UGGH was where the through-hole legs were all bent over flat against the PCB. During desoldering, I had to straighten each leg so it would pull through without destroying the hole. I just did 10 f2uee pushbutton switches like this. Like they needed to be held in better?? I was sweating bullets trying my hardest not to lift a trace. I did but it was fixable. |
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Post by jimwilliams on Jan 4, 2016 10:35:20 GMT -6
I fixed one of those back in the 1990's for the "Viper Room" on the Sunset strip. They were desperate so I took it on. I found a shorted out tantalum psu bypass cap and replaced it, good to go. It was their only reverb box for the club. They had their private PETA celebration set for that night with the Pretenders playing. I got a couple of comps for saving their @ss and went to the "party". I got to rub up against Pamala Anderson in the narrow hallway to the restrooms. Little Bill Mayer was also there and I made a few people eating tasty animals jokes, he didn't think I was funny, the feeling is mutual.
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Deleted
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Post by Deleted on Jan 4, 2016 13:09:54 GMT -6
Oh, Mrs. Anderson was a hot girl in the 90's plus she always had a faible for musicians....
Uhm, what were we talking?
Oh, Lexicon repairs. A while ago Volker (silent:arts) posted some stuff on facebook about a Lexicon repair if i remember it right. It is crazy stuff with all these obsolete parts, part no.s where you don't find out what seemingly proprietary chips are actually doing ... obviously this is a challenge of it's own, vintage digital repair...
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Post by donr on Jan 4, 2016 16:40:18 GMT -6
I got to see Pam Anderson a few years ago when BOC played with Kid Rock at the Buffalo Chip in Sturgis. She's quite attractive in person. I wouldn't want to rub up against Bill Maher though.
I had a PCM 70 that the firmware chip pins got wobbly on. My buddy has it, I think it still works.
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Post by guitfiddler on Jan 8, 2016 23:24:07 GMT -6
I have some older Sony boxes that have huge noise problems, they used to sound amazing.
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ericn
Temp
Balance Engineer
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Post by ericn on Jan 9, 2016 21:33:39 GMT -6
Chris you are one stubborn SOB! And you know I mean that as a compliment! the question is was it worse than a sewer robot ?
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