Lab Series L5 Compressor Problem

[bdonova1]

I have an L5 that I bought new around 1978, and it worked fine for many years.  First, the reverb quit, and it was nothing simple, so I ignored it.  Then the clean channel started generating static, even when  using the other channel, so I disabled the clean channel, since I rarely used it.  Then a couple years ago, I bought another amp, and have been mostly using that.  I always intended to take a look at the L5, and recently when I tried to use it, channel 2 was all static, increasing after on for a minute or two, with the volume changing along with it.  Also, the compressor LED is on even when the compressor is switched off.

So I started looking at it, and replaced A201, A109, CR101, CR102, and CR205.  I found CR205 to be shorted, and I was blowing one of the fuses between the transformer and the rectifier.  Strangely that fuse (and it's twin) isn't on the schematic.

Anyway, the reverb seems to be working, and the noise is gone, and it seems to be steady volume.  But the compressor LED is still on all the time, even with it switched off.  When switched on, I don't believe it is working, and I do know how it is supposed to work, as I used it for years.

Any thoughts and ideas would be appreciated.  I don't want to ignore this one, I always liked the compressor on this amp.

Brian

[bdonova1]

Well, I had a 4558 handy and the amp half apart, so I replaced A112.  Looking good so far.  LED is off when compressor is off, and when compressor switch is on, compressor LED will come on if master volume is up high enough and there is a signal from a guitar.

I still have some popping from the speaker when I power off, but it has been occurring so long, I can't remember if it ever behaved differently.

It's late so I will check it out more thoroughly tomorrow. 

[Roly]

Well that's good news, thanks for reporting your success.   :dbtu:

Re: your turn-off pop, we covered that in a thread here a while ago;

http://www.ssguitar.com/index.php?topic=2439.msg19970#msg19970

HTH

[bdonova1]

It certainly seems to be working normally again.  I don't have any test equipment to do the adjustments, but it seems to be working fine.  Though I got by without any help this time, I did get some good info from previous posts and replies.

I found all the original documentation.  I bought it on Feb. 13, 1978.  It came with an envelope of service documentation (schematics and board layouts), and owners documentation (simple users guide and where to get warranty service).

I even have the little tags that hung by a string of the various controls touting the merits of the Multifilter etc.

I like the amp, you can get a good crunch from it, and the compressor is nice.  The only thing I regret is I sold a year old Marshall 50 watt combo to buy it.  I thought the Marshall was boring and hadn't played with effects pedals yet.  Oh well.

If my repairs last another 35 years, I'll be 91.

Brian

[Roly]

If my repairs last another 35 years, I'll be 91.

... and doling out advice on SSguitar.   :lmao:  :dbtu: