Repair of my Lab Series L5

[Susanne]

i am writing in the name of my husband, cause my english is little better 

We have a little problem with our L5 Amplifier. My husband did not use the L5 for a few years. But now he started playing his guitar again an used it for a couple days. It worked fine until yesterday.

The functions like "Reverb", "Frequenzy" and "Multifilter" now sound very strange, and one fuse of the Powersupply blow. (see on the picture, if i get it attached :-)).

I have no idea, where I should start searching for the mistake. I am a electronics technician, so I can measure and change broken parts, but I have no Idea how this amp works.

I checked all boards by looking, could not find any burning marks, or broken parts.. Where sould is start?

[J M Fahey]

Ok, welcome to the Forum

1) please search for the full Gibson Lab L5 amplifier schematic, it might even be inside SSGuitar , and post it here, so we all talk the same.

2) don´t know what your fuse connects to, let´s wait for the schematic, but your picture shows *one*  red circled empty holder, yet there is another empty one on top of it.

3) where are you from? What is your mains voltage?
Is the amp plugged straight in the wall or does it use a transformer?

4) after we sort this fuse problem, maybe you might try to record and post that "strange sound" 

[Susanne]

Thanks for your answer J M Fahey..... will try to answer the question

1. The schematic will be attached........ or they are easy to see at http://www.rru.com/~meo/Guitar/Amps/Lab/schem.html

2. Yes there are two fuses, the other one did not blow, just took it out for the pictures, the fuses are 2,0 A at 250 V. The red circeld blow.

3. I am from Germany and we have 220 V AC

4. I will ask my husband to record the sound. To my ears, this functions do not work at all........ i can hear no difference.


When i believe to my husband (), they worked before. I guess the problem appeard, because he did not use that thing for many years, and ist was in the basement. ....... But he loves to play with it, an so i try to repair it.............

Thank you very much for your help,
Susanne

[J M Fahey]

Ok.  I see no 2A fuses whatsoever on the schematic.

The main supply ones F21/F22 on the secondary side are either 5A for the 100W version, or 10A (indicated by a number 8 inside a triangle)  for the 200W one.

On the primary mains/220V side, regular Lab L5 does not use plain "thin wire inside a glass tube"  fuses but resettable "circuit breakers" , miniature versions of what´s currently used on home electrical panels.

That said, *maybe*  original USA made circuit breakers were not type approved under strict German Electrical Safety rules and they opted to use plain fuses instead, so please check what goes through those fuses.

Now that I think about it, Euro rules demand "fuses on all transformer windings", those *might* have been added on the low voltage supply (+/-25V raw, +/-15V regulated).
Missing one would certainly make amp soound funny, but please check what they connect to first.