radardoug
Well-known member
Better to use the same speed, but you wont do any damage. It will either work or it wont.
lexicon model 200 & pcm60 need repair
- Thread starter axisdreamer
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Help Support GroupDIY Audio Forum:
Thank you radardoug!
I have another question to help me understand how things work...
How is it that switching the (presumedly) faulty DRAM IC with the other 3, when the four seem to be in parallel, upgades or worsens the issue ?
Initially, this IC was in position 3 (U23, if I put it in position 4 (U26 it is a little better, but in positions 2 or 1 (U21 / U18) it gets far worse...)
Lexicon PCM60 schematics DRAM
I have another question to help me understand how things work...
How is it that switching the (presumedly) faulty DRAM IC with the other 3, when the four seem to be in parallel, upgades or worsens the issue ?
Initially, this IC was in position 3 (U23, if I put it in position 4 (U26 it is a little better, but in positions 2 or 1 (U21 / U18) it gets far worse...)
Lexicon PCM60 schematics DRAM
radardoug
Well-known member
The dram address lines are in parallel, but the data lines aren't. Unless you know that you have good drams, probably best just to change them all, and then you can go back and test the removed ones one at a time.
The RAM devices probably form a wide word, and you are moving the fault between lower and higher order bits in the audio words.
I've ordered a few DRAMs so I'll be able to check the original DRAMs one at the time.
radardoug
Well-known member
Lexicons are nice, but the old ones are tricky. My 224XL was going fine, and I was using it for some testing yesterday, and now its crapped out!
Throwing a NVS rom error. I've just replaced all the sockets on the NVS card that I previously had not, and its still faulty! Going to be a long day.
Throwing a NVS rom error. I've just replaced all the sockets on the NVS card that I previously had not, and its still faulty! Going to be a long day.
I feel your pain but your knowledge with these units seem deep. I have a model 93 that shutdown after being on for 10 mins. I suspect It’s tants in the power supply. I’m going to try to bring back to life in the new year.
radardoug
Well-known member
Well, finally fixed it, had to get serious and pull out the extender card. Turns out that it probably was dodgy sockets, but in the process I did miss a connection on one of the changed sockets. For future info, it looks like the Lexicon will default to an H01 or H02 error if it cant actually find the eproms.
Following my familiarity of digital periodic noise now, I remembered a lex PCM41 that was shelved along time ago. It uses 4116 dram chips. Those were common computer mem chips in the 80s. I had a couple of motherboards with 4116 chips before my move out of Denver. I replaced 6 chips and I’ll be if it didn’t fix that piece of gear. It sounds great.
It needs a recap with 45 year old caps but the supplys are clean and measure correct.
It needs a recap with 45 year old caps but the supplys are clean and measure correct.
radardoug
Well-known member
Working on a 200 today that had multiple faults. I got it down to the gain ranging Prom being faulty. With the help of a couple of people overseas I got a copy of the prom and woohoo! it works! The 200 would not start though first thing. Yet another resistor in the reset circuit with corroded legs.
Hello, does anyone know what this error means?
The unit powers up ok and works alrigth... for about 10 minutes to 3 hours. Then it reboots as if I pressed the reset button. This can repeat many times until I switch it off and on again. Then it might work or not.
Can this be the power supply?
The unit powers up ok and works alrigth... for about 10 minutes to 3 hours. Then it reboots as if I pressed the reset button. This can repeat many times until I switch it off and on again. Then it might work or not.
Can this be the power supply?
living sounds
Well-known member
It can be many things, probably related to temperature. My 200 is the opposite, it usually works well once it has been on for a while. It often shows a memory problem on startup, I've changed them all to no avail.
jensenmann
Well-known member
Every 200 I had on the bench needed a recap. There are many tantalums inside which are slowly dying. I always found one that turned into a resistor.
And make sure that the memory battery is ok.
And make sure that the memory battery is ok.
radardoug
Well-known member
The battery will gas and cause lots of problems around the reset circuit, which is quite complex. In the one I was repairing, I had to completely rebuild the reset circuit.
