Dead Lexicon PCM70, need some help.

[radardoug]

I am working on a Lexicon PCM70, it has no reverb, otherwise everything functions. I bought an HP signature analyser and went through it with that, all chips give right signatures except two, but replacing those chips does nothing. I am starting to suspect two programmed chips in there, U48 and U49. I do have a reader, but need a working unit to read the chips in. Can anyone help?

 

[cavedata]

I am working on a Lexicon PCM70, it has no reverb, otherwise everything functions. I bought an HP signature analyser and went through it with that, all chips give right signatures except two, but replacing those chips does nothing. I am starting to suspect two programmed chips in there, U48 and U49. I do have a reader, but need a working unit to read the chips in. Can anyone help?

 

[radardoug]

Awesome Cavedata! I was thinking about this unit this morning and thinking I might have to declare it unfixable. Back to work! Thank you so much.

 

[radardoug]

An update on this one. The 74s288 has one byte wrong out of 32. I will get another one burnt and update.

 

[Ivan Blajer]

G'day any update on this? I have PCM70 with teh same problem no wet signal. Also the level meters pegs to max after you load a program.

 

[radardoug]

I have someone testing the CMU chip, but it will be a while. Sounds like your problem may be different. Get the manual and spend many happy hours working on it!

 

[amoreno]

Hello, I have a unit with no wet audio too. Please could you tell me which programmer you have? if you put W8 jumper in s-t do you have signal on tp1/12? because I have signal, so maybe a high speed processor problem and u48/49 are very hot. I try to replace but need a programmer to dump the files that are in the post. I swap memory and nothing change. BR, Antonio.

 

[radardoug]

I get the GALs programmed by a guy on Ebay. His email is [email protected]. He does this as a service. You need to provide him with the GAL files. But its more likely the CMU is faulty.

 

[radardoug]

I have just done a board which will replace the CMU chip. I'm getting them made, and will post if they work.