lexicon model 200 & pcm60 need repair

[radardoug]

Better to use the same speed, but you wont do any damage. It will either work or it wont.

 

[tupinamba]

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

 

[radardoug]

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.

 

[ccaudle]

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 ?

The RAM devices probably form a wide word, and you are moving the fault between lower and higher order bits in the audio words.

 

[tupinamba]

Thank you for your answers ! That makes sense... I've ordered a few DRAMs so I'll be able to check the original DRAMs one at the time.
I'll keep you posted when I receive them!

 

[fazer]

Working on a PCM60 right now also. It creates reverb but is noisy. The periodic noise I’m hearing sounds like a dram problem as mentioned earlier. I’ve ordered some NOS Dram to replace and see.

 

[tupinamba]

I've just received the NOS DRAM I ordered and, as excepted, this solved the issue and now the unit is perfectly noiseless!
I hope the result will be the same with you fazer!

 

[fazer]

Got the DRAM CHIPS for my pcm 60. Installed and periodic noise is gone. Output is clean quiet and sweet sounding. Yeah!

 

[tupinamba]

Bravo! Always nice when it's an easy fix.
This reverb unit is really nice.

 

[radardoug]

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.

 

[fazer]

Lexicons are nice, but the old ones are tricky. My 224XL

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, 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.

 

[fazer]

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.

 

[radardoug]

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.