lab series L2 head problem

[decoy3a]

I am having trouble with this beauty. I turn it on and no lights, sound, or action. I have a load on and when I first turn it on I hear a thump and then nothing. It had a burnt resistor I changed but I don't know if it is still the problem. I changed a transistor that was going bad. Any help is very needed. I am extremely dedicated to this amp and will take it to an expensive tech if needed.

[teemuk]

I guess you need to pinpoint the area of the faulty circuit in a greater depth and also provide us with a bit more details if you want help. For example, what burnt resistor and where, and what transistor was going bad. That amp has plenty of resistors and transistors, you know.

Then, is there, for example, an effect loop that you could use for pinpointing the fault to either preamp or power amp?

I guess that it's also wortwhile to use some kind of form of current limiting since if something is seriously bad in that thing (e.g. shorted output) it can easily take other parts and circuits with it - as well as nullify any repair work you've done previously.

Removing the load is also recommended while you troubleshoot and fix but that can be difficult in practice if you lack equipment to scope the output.

Out of curiosity, how close to Lab Series models L5, L7, L9 and L11 are these things? L2, that was a bass amp, right? I guess there's a good chance that at least the power amp is similar - if not identical.

[Jack1962]

Yes this is 100 watt bass head, but need tons more info bro.


                                 Rock On

[decoy3a]

yeah I can't really tell by the schematic I have for it where and what all I changed. Thanks though I am just going to take it in and bite bullet. I will just mess it up more I'm sure. Does anybody out there have another one of these they don't want. I use mine for jazz with a gretsch new yorker hollowbody and an ampeg 15. Better eq in my opinion than the roland JC 75.

anyway thanks and I love this forum, alot of info I have been looking for