Lexicon 224 - Distorted

[sonicmook56]

Hey all, I know there are some Lexicon experts that frequent this form so, if that's you and your reading this, I have a few simple questions.

First off, I generally don't work on this type of gear at all so please excuse my ignorance.

What I have here is a Lexicon 224 reverb that sounds very distorted. All the power supply voltages are healthy and look good on a scope. Upon power up I get error message "E91" on the remote's display. I referenced the service manual and learned that this error is a "memory error". ok, easy enough. I found replacement RAM chips from an online vendor and went ahead and started swapping out each chip for a new one and listing to the output. Eventually all chips were completely swapped out and output distortion did not change. One weird thing about the "E91" error is that the owner said that came on every time and it worked great, so this error might just be a glitch?

Digging into the service manual a bit more I found you can force the unit into self test mode by removing cards DMEM, T&C and ARU from there sockets. Powering up the unit in this mode allows the audio to pass, and it's STILL very distorted. This is where I'm stuck. I'm not sure what I need to troubleshoot next. I don't have any extender boards so I can't see getting a 'scope probe on the A/D and D/A boards to look around.

The only cards in the mainframe are the SBC, FPC and the Ain and Aout cards, so the fault must be on one of these. I might try replacing the caps on the FPC board.

The P.S. decoupling caps on all the cards are tantalums. Is it safe to replace these with an equivalent electrolytic?

Thanks for reading this.

 

[wtmnmf]

The 224 is a Multibus ll device. You can look for a Multibus ll extender. I got mine after a bit of searching at a good price, but be careful of the vintage industrial computing sources, as they tend to charge insane prices.

 

[dbbubba]

I have an E91 error.

What did you ever discover as being the problem?

I also have E31 showing at boot=up diagnostic time.

 

[pucho812]

it was once recomended to me  to make sure the edge connecor is clean as that can cause issues but I doubt that is the problem in your case. I hada similar problem with a 480L  a few years back.
since the 480L has 2 engines I tried it with just on of the reverb cards. I forget what they refer to them in the repair manual. It's been a while. The unit worked without the distortion.  Then I tried the other card and got was dostirtion and random clock noise . Sent it back to lexicon where they replaced a couple of chips and reset the jumper pins into the right position. IIRC they will still fixthe 224 cards. If you can isolate which card is the problem then you can send that back to them and for like 250.00 dollars  they will repair it. Sometimes it's easiest to do that with digital gear.

 

[sonicmook56]

Card edges are clean, but maybe the contact tension is loose?

It's been sitting on the back shelf.  I'm frustrated with it because it's very difficult get a scope in there to see what's going on without the extension boards.

I have narrowed it down to either the A/D or D/A board.

Wish I could look at data lines and see where it gets distorted.

E91 error is bad ram.  If you can't hear a problem, the bad ram chip could be assigned to a lower bit in the noise floor.  You can yank that card out of the chassis and it will still pass signal, except without the effect.  See if it still gives you the error.  Can't remember what E31 is.

 

[kilmister]

The 224 is a Multibus ll device. You can look for a Multibus ll extender.

Hi!

I have problem in my 224XL and looking for extender board.
I found this from Digikey: http://media.digikey.com/photos/Vector%20Photos/3690-18.jpg
I suppose it's right but just want to make sure I'm looking correct board.

Thanks in advance,
Paavo

 

[radardoug]

I have extender boards available, $50 US plus postage. Some of your problem may be opamps in the filters, a common fault with these.

 

[kilmister]

Sounds better than Digi-key  ;D

Problem is defenetly in AOUT board. When it's attached all +/- 15V rails drops down near to zero volts and all output transistor becomes quite hot.
When I got the unit I've been told that U4 on AOUT board blows repeatedly.

-Paavo

 

[QUEEF BAG]

Hmm, are the 224 extenders and 480 extenders the same?

I'm definately gonna be needing one in the next few minutes.

 

[Jules123]

Hello Paavo (and of course anyone else who can help)

i hope you read this, it`s been some time since this thread was opened...                                          Did you find a solution for your 224? I have a 224XL with almost the same problem, everything seems to work fine when the AOUT Board is pulled (correct voltages at test points, meters show input on larc, no error codes).
When it`s installed, some voltages drop extremely and meters show no more input,  very low and distorted output with hum, but no error codes at all.

thanks

Julian

 

[radardoug]

As on all this old gear, tantalum decoupling caps tend to die. Check your power supply rails on the Aout card for shorts, bound to be tantalums. Also add leds on all the supply rails, then you can see at a glance that you have lost a rail.