ADA MicroTube 100 Popping Fuses

[PepeSilvia]

So, I'm on my second ADA MicroTube 100. The first one I got with no channels working when I was just setting out learning repairs. The second I got half working in a package deal.

Both of them do the same thing. As soon as you power them on the fuse pops. The first one is in both channels. The second is in one channel only. Does anyone have any experience with these and know if there is a common problem, or check out the schematic and give some tips? Obviously a shorted path to ground, just don't want to waste a lot of time checking individual components when someone in the know could tell me right off the bat.

[Jazz P Bass]

Do you have Sheet #2?
It appears that the output section high voltage rails are fused.
Remove them for power on test.
Remove the tubes.
See if it powers up & holds the fuse.

[PepeSilvia]

There are no tubes in the power section. Next best thing would be the transistors, but I figured they'd be more robust than a tube, and unfortunately, they aren't in a neat little socket...

[Jazz P Bass]

O/k, you said "as soon as you turn it on the fuse pops."
As there is no schematic for the power supply, I am at a loss as to which fuse "pops".
It helps everyone if you can be specific as possible.

I do not see any components in the output section that cannot be checked with a meter for a short.
have at it
And I would have to recommend that you build a "lamp limiter".

[PepeSilvia]

Sorry for the lack of clarification. The schematic I shared was for the second channel. The other sheet is the other channel, which is identical. I think the power supply is not an issue here, the fuse is on the schematic I posted (F101). I read a bit about the lamp limiter, does it just consist of a light bulb in place of the fuse, the brightness will tell you how much current is passing while at the same time limiting the amount of current that the circuit can get?

[PepeSilvia]

Well, according to my meter I'm shorted across the source and drain, from the gate to the source, and from the gate to the drain on IRF9530 (the P-channel MOSFET) and shorted from source to drain on IRF530 (N-channel). Guess something fried them? I'm hoping I won't replace them and have the same thing happen.

[Jazz P Bass]

Lamp Limiter

Guess something fried them? I'm hoping I won't replace them and have the same thing happen.

Check all the transistors in the output section.
Check all of the resistors & diodes.

[PepeSilvia]

I'm not sure what you're suggesting I do with the lamp limiter. Is the purpose of it just to prevent my from blowing fuses every time I want to test it?

[Jazz P Bass]

Come on.
It limits the current that the amplifier can draw from the mains.
You have a blown output stage.
You must check everything in that stage.
If you inadvertantly "missed" something and the amp draws way too much current, the lamp will stay bright.
An amp that is functioning properly will briefly illuminate the lamp as the power supply caps charge.

[riz]

I recently built my first bulb limiter. It's an awesome, simple tool. Follow the advice given, build one, and use it. Your voltage readings will not be accurate, but that is not the point of using the limiter. The point is to safely troubleshoot the circuit until you can repair it and bring the power up on regular mains.