Hartke B300 Fuse blows everytime its plugged in..

[andresphere]

Hi all,
My friend has come up with his Hartke B300 Bass Amp.
The problem in it is that everytime I plug in the amp in the mains outlet, the fuse blows....The 2nd time i replaced the fuse, the fuse inside the amp also blew. I checked for shorts in the power output transitors too...there aren't any shorts.
The transistors are D2059.
Can anyone troubleshoot this problem for me please?
Also it would be helpful if someone could post the schematic.

Thanks In advance!

[olddawg]

Have you checked for a shorted rectifier, regulator, cap or transformer in the power supply? Are you sure you are measuring the output transistor junctions correctly? The best way is to remove the transistor or float the emitter and base.

[andresphere]

I checked only the transformer..both primary and secondary. I was getting acceptable resistance at both the ends.
I still have to check the rectifier and the caps!
There seems to be a dry solder at both the resistors which are connected to the base of the transistors.
Can that be a problem?
Or the fuse blows just because of a SHORT?
More bit of information,
this problem started accusring after the amp switched off after a sudden power failure.

Thanks for the reply anyways

[andresphere]

I am getting a resistance of around 18 Mega Ohms on 2 rectifier diodes when I am testing them on a reverse bias....Is that a problem???

[DrGonz78]

Are you measuring these diodes in circuit or not? Sometimes measuring the diodes in circuit will make it see other components that run parallel to your measurements. I will assume that you are measuring in circuit, but if not those diodes are fried. However, 18M ohms is quite significant... Are you measuring the resistance of the diode or the using the diode checking setting on your meter? I know on my meter it will go up to 1.3 or 1.4 and sit there while in circuit. Other times it goes up to almost 2 and then you get the I. Just something there to chew on if it helps any, good luck.

[andresphere]

I measured the diodes in the circuit itself....And yes, I am checking the diodes on the diode testing setting on my multimeter...
Please help!
I am stuck!!

[olddawg]

I measured the diodes in the circuit itself....And yes, I am checking the diodes on the diode testing setting on my multimeter...
Please help!
I am stuck!!

Can you post a schematic? Are you sure you don't have a shorted output? Divide and conquer. Isolate the power supply.

[andresphere]

I dont have the schematic either!
Please help!!
I AM LOST!!!

[mozwell]

various samson / hartke sch attached
hopefully one of these will be close.
i dont have B300, but i am attaching any sch i have that uses D2059 / 2058 / 2155 etc

disconnect the transformer secondary wires, and then carefully measure the AC volts (dont touch the wires of course), are you getting the right voltages.
disconnect the power amp board, connect the rectifier & main filter caps, do you get proper DC volts on the main filter caps.

disconnect & measure the power transistors AND the driver transistors, do they all measure ok, ie not shorted C-E

[Enzo]

No schematic? COntact Samson and ask for it.

[andresphere]

The amp is fixed for now!! The rectifier diodes were causing the short in the amp! Thank You once again everyone for your help and the schematics!!
Thank You!!

[andresphere]

No schematic? Contact Samson and ask for it.

I mailed them about this problem, they gave me the number of their authorised service center and rejected to provide me the schematic. When we went there, they asked us $50 for that repair....!
Was that worth?

[Jazz P Bass]

$50.00 to repair an amp.
Sounds worth it to me.