DV Mark LJ Exploratory

[Alder Statesman]

As I mentioned in another post, my Little Jazz is acting up. After playing for twenty minutes or so the amp begins to distort and not in a desirable or predictable way.

This evening I opened it up hoping to maybe find a loose connection or something obvious.



Really not a lot for an old tube guy do mess with. The chassis has a small printed circuit motherboard, two smaller printed boards, transformer, and a combination heatsink cooling fan. The speaker is labeled as DV Mark and is held in the cabinet with eight screws and mastic. The cab is insulated.

The caps looked find which was not a surprise as the amp is less than three years old.

Seeing nothing obvious, I put is back together. Played for less than a half hour, but not not problem. Perhaps removing and then reseating the speaker spade terminals did the trick.

Updates to follow.

[Gabor]

Is the fan spinnig? The sympthoms you are describe (after 20 minutes...) may indicate overheat some transistor, so change its characteristics and malfunction.

[Little Jay]

My guess would be a heat related problem as well.....

[Alder Statesman]

Is the fan spinnig? The sympthoms you are describe (after 20 minutes...) may indicate overheat some transistor, so change its characteristics and malfunction.

I will check that out if it distorts again. Thanks!

[Little Jay]

It could be worth inspecting solder joints to look for cold joints or fractures. I had circular fractures in solder joints in my Fender Blues Deluxe amp, only visible with a magnifying glass, that caused all kind of random symptoms when they warmed up and caused intermittent contact. Reflowing them solved all the problems. I don’t know how warm a DV gets but since it needs a fan it might get warm enough in places to cause this kind of phenomena?

[entresz]

My LJ runs fairly warm when I'm gigging with it - I usually have it turned up to 4-5.
Certainly warmer than other solid state amps I use. I suspect the tiny cabinet doesn't help with this.
No issues yet, fan comes on when it needs to.

[Alder Statesman]

Finally had some time to play. Put in about 90 minutes this evening and had no problems. Reseating things must have done the trick.