Lexicon 480L HSP Board Repair?

[tommia]

Before I take my desoldering station. I'm still wondering: how is it possible, a shorted tantalum fried the powersupply, that's to be suspected. But why would the DRAMs on both boards be affected by that?

 

[plimousse]

Get the test cart ( available on Ebay ?), it will save you hours of guessing.
And follow the chapter 5.5 of service manual.
With the test cart, you get the result immdiatly.
Cheers,

 

[NoisyIndividual]

I've never spent hours guessing, and I have replaced lots of faulty DRAM in my time.

A pair of ears, and a systematic logical approach finds the duff ones quite easily and quickly.
But then I'm old, and we didn't have DRAM testers in them there days.

Freezer spray can also help, as DRAM chips don't always totally fail on every memory location.
But I think you'll need an extender card to do that in a 480L.

 

[tommia]

If it would be my unit I would buy the test card. The owner desided not to do. Where can I fînd an extender card? I ordered some HY53C464LS-10 on ebay. If it doesn't help, we have at least some spares for the future.
And you couldn't imagine: he just sended me a text message today: My 960 broke ! I don't know if I take that challange. But first things first.

 

[tommia]

I extracted HSP board 1 and left it alone for now. I removed Dram 64 to 68 on the other board and I plugged it back in. OVLD leds are out, noise is gone, got some reverb and some kind of multitap delay on the sound of a vinyl record that has come to his end. Very promissing if you ask me. I have to order some 18 pin sockets now. Thanks so far

 

[tommia]

You guys are geniuses! I replaced bad DRAMs (64,65) on the first HSP board. Works now as it should, time for the second HSP board.

 

[tommia]

Unit is completely repaired. Thanks to Noisyindividual, Paolominarini, Philbo King for the great support. What I found out is that you only need the last 5 drams for the long reverbs. For chorus you only need the firt 5 drams. So if you have incorrect reverb the problem is in the last 5 drams.

Strange thing is that I had a problem with the last 5 drams, when the DRAMs switched places, the problem was gone? We will see after burn in.

 

[tommia]

Burn in, all good.

 

[Quantum J Audio]

My 480-L was doing weird things on one output. The levels where one sided on the B machine. This was solved with a factory reset. the reset worked and all is running fine now.

To clear the memory, do the following:

1. Power the machine down.
2. Open up the front panel and remove the Host board (all precautions must be taken against static!)
3. Locate the U38 and U39 (directly behind the ROMs.)
4. Remove U38 and U39 from their sockets and short all of their pins to ground (The side of the chassis is ground
   if the machine is plugged into a grounded outlet, as it should be.)
5. Reinstall the chips into their sockets (polarity is important!)

When you first power the machine on it will say “No Program.” Do not be alarmed, just load a program as normal (press any number on the LARC.)

Make sure you load a new patch into both machines. I only loaded the A machine and weird stuff happened with the A&B machine routing of signal, which confused me for a while!

Full service manuals uploaded to the forum. I'm about to recap and put a quiet fan in mine. Double the originals air flow and only 12dBa. Will need to add a voltage divider for 12v operation.

 

[RandomHall]

Get the test cart ( available on Ebay ?), it will save you hours of guessing.
And follow the chapter 5.5 of service manual.
With the test cart, you get the result immdiatly.
Cheers,

 

[michaelpnielsen]

I'm having a real hard time getting the drams out. Wick, desoldering gun.... did you guys get them out or did you cut the legs?

Thank again

 

[radardoug]

You need a good desoldering gun. Otherwise you will ruin the pcb.

 

[Khron]

I'm having a real hard time getting the drams out. Wick, desoldering gun.... did you guys get them out or did you cut the legs?

Thank again

Extra solder & flux, and temperature-controlled hot-air station / gun?

 

[paolomunarini]

I'm having a real hard time getting the drams out. Wick, desoldering gun.... did you guys get them out or did you cut the legs?

Thank again

I went with flux and desoldering gun.

I didn't have to apply any excess solder. The flux did its magic.

 

[NoisyIndividual]

If you are having problems with the equipment and technique you currently have, I would advise you cut the legs instead.

You will almost certainly not damage the board this way which at the moment is your prime objective.
You don't really want to be learning skills on a 480, do you.

 

[RandomHall]

I'm having a real hard time getting the drams out. Wick, desoldering gun.... did you guys get them out or did you cut the legs?

Thank again

 

[RandomHall]

A little hint:
take a working DRAM chip and bend its pins a little inwards.
Have your 480 setup so that you can
hear the fault.
Press the working chip down on one
of the suspected DRAM’s.
TAKE CARE aligning pins properly.
You might get some instant noise due
to the rather rude connection.
But if the fault sound goes away, you
have then found the faulty DRAM
so replace it.
If not try the next and so on.
( a situation with more than 1 bad DRAM can of course occure.)

This hint is for a quick fix and has worked for me so many times.

Best thing to swap all chips.

 

[RandomHall]

A little hint:
take a working DRAM chip and bend its pins a little inwards.
Have your 480 setup so that you can
hear the fault.
Press the working chip down on one
of the suspected DRAM’s.
TAKE CARE aligning pins properly.
You might get some instant noise due
to the rather rude connection.
But if the fault sound goes away, you
have then found the faulty DRAM
so replace it.
If not try the next and so on.
( a situation with more than 1 bad DRAM can of course occure.)

This hint is for a quick fix and has worked for me so many times.

Best thing to swap all chips.

I just forgot that I have the original
extenderboard.
The DRAM trick is a little more complicated without.