outoftune

Is there anyone who repairs Lexicon PCM 42 or PCM 70?
« on: October 17, 2010, 02:58:22 PM »
I've tried David Kulka but he said he doesn't offer repairs for these. I have contacted Jim Fabiano at his recommendation.

Is there anyone else out there who might be able to help with these units?


chriss

Re: Is there anyone who repairs Lexicon PCM 42 or PCM 70?
« Reply #1 on: October 17, 2010, 05:18:07 PM »
Don't be a killjoy - describe the problems of the units... Then in return I tell you how I repaired one of my PCM70's myself. (I guess you already found the PCM70 Service-Manual somewhere around here?)

Chriss

QUEEF BAG

Re: Is there anyone who repairs Lexicon PCM 42 or PCM 70?
« Reply #2 on: October 17, 2010, 05:54:39 PM »
it seems to be up to us at this point.
good lex repair people are hard, if not impossible to find.

yes, describe problems, we might be able to help.
schematics are available from the lexicon ftp website.

what we really need is someone who can blow e-prom chips for
the various models.
that is an unfilled niche - (that was a hint to anyone...)

chriss

Re: Is there anyone who repairs Lexicon PCM 42 or PCM 70?
« Reply #3 on: October 17, 2010, 06:05:46 PM »
Hm, I got both sets of EPROMs (V2 and V3) for the PCM70 and I have something like an EPROM-copy-machine in the basement that I never have tried to use, but I wonder if that would be legal to do...

outoftune

Re: Is there anyone who repairs Lexicon PCM 42 or PCM 70?
« Reply #4 on: October 18, 2010, 09:31:56 AM »
If anyone here is able to help, that would be amazing.

The PCM 70's issue is that there is a problem with the decay of the reverb. The effect works but the tail gets distorted and the decay sounds strange.

I have recapped most of the unit, going to finish that out, but it hasn't helped the problem. I have the service manual. I have checked the the analog section on 0% mix and it is functioning fine. So as far as I can tell, it seems to be a digital problem. Any suggestions folks?

chriss

Re: Is there anyone who repairs Lexicon PCM 42 or PCM 70?
« Reply #5 on: October 18, 2010, 10:29:44 AM »
I did not have this problem myself but have haerd/read about it. As far as I remember the suggested solution was to change the ram-chips because they obviously tend to fail from time to time. Have you googled around for that problem?

Arno

Re: Is there anyone who repairs Lexicon PCM 42 or PCM 70?
« Reply #6 on: October 18, 2010, 10:36:10 AM »
The PCM 70's issue is that there is a problem with the decay of the reverb. The effect works but the tail gets distorted and the decay sounds strange.

DA convertor?
Does the beginning of the reverb sound distorted too when you reduce the level?
Ie, the dac distorts as soon as the level drops below a certain point? or is it specifically the tail of any reverb at any level.

chriss

Re: Is there anyone who repairs Lexicon PCM 42 or PCM 70?
« Reply #7 on: October 18, 2010, 03:57:44 PM »
Hey Arno,
with my PCM70 it WAS the DAC. And with fault-searching I found out three interesting things: 1) The unit uses one DAC for 3 signals! In, Out L and Out R, this all via multiplexing the DAC (I think it's successive approximation for the input... Well - it's an 80's piece of gear...). 2) It's a 16 bit unit, not as often said a 12 bit and 3) All these dbx VCAs don't make a compander-system but are only for the dry/wet-mix!

O.K. but the effect with the dead DAC was: There was nothing at all coming out when in 100% wet, but everthing nice and clean when in 0%.
So therefore I doubt that "outoftune's" unit lacks a new DAC (which is hard to find and if - expensive...). But I wouldn't swear so.. My first suggest: Re-RAM the unit. It's the least expensive step after recapping, so... But be careful not to order SMD's!

Chris

outoftune

Re: Is there anyone who repairs Lexicon PCM 42 or PCM 70?
« Reply #8 on: October 19, 2010, 02:54:07 PM »
I will replace the RAM after I finish the complete recap.

Dumb question...but what chips are the ram? I combed through the service manual and saw many mentions of the RAM, but didn't see what specific chips are mentioned.

chriss

Re: Is there anyone who repairs Lexicon PCM 42 or PCM 70?
« Reply #9 on: October 20, 2010, 07:42:07 AM »
The RAM is the 4064 chips U30, U31, U44 and U45. But be sure to first check everything that the manual suggest for testing to get closer to what the problem may be.


 

Related Topics

  Subject / Started by Replies Last post
3 Replies
2322 Views
Last post April 30, 2012, 11:42:25 PM
by CJ
1 Replies
1774 Views
Last post May 23, 2013, 06:51:02 PM
by kosty
0 Replies
273 Views
Last post January 14, 2020, 12:30:34 PM
by easymix
3 Replies
468 Views
Last post June 13, 2020, 10:18:54 PM
by Whoops