Blowing my fuse (s)

[Jimlondon]

Hi All.
I found a post in the archive about Marantz amps blowing fuses, which is exactly what my Marantz PM55 SE is doing right now.
The fuse is a 1.6A T (slow burn?) & the only components in the circuit before the fuse are the power switch and a capacitor.
The previous post only suggested putting in a slow burn fuse, which mine already has & this matches the rating on the PCB.
Any ideas as to what the prbolem may be?
Please help, I'm stuck with no music & can't afford to send it away, the postage alone would be a fortune!!
Thanks in advance.

[Nuuk]

Sorry to break the news Jim but it looks like your amp has a problem somewhere!

You have a few options but any of them is going to cost you something.

You could try finding the fault and repairing it yourself. Not recommended unless you have a bit of experience.

You could try a local TV repair man and ask if he will have a look at it for you.

You could buy a replacement s/h amp.

You could build a Gainclone.

The latter at least will give you a big improvement in sound quality for your outlay.

The problem is probably with a transistor somewhere.

[chris ma]

Try post a note in the canteen of your local Polytechnic. May be the student union noteboard or something. Some 4th year EE students should be able to help, especially for those that like a challenge.

Good Luck!

[Jimlondon]

Thanks for the suggestions guys.
I have a few options for repair shops but in my experience around here they will always charge £30 just to open the case then at least another £40 to do anything. For £70 these days I can probably pick up a new amp of comparable quality.
I do have & can use a DVM but don't really have a clue how to use it to track down faults in this sort of kit, any suggetsions for beginners guides? Maybe I should go back to college myself.
Otherwise, does anybody want a non running Marrantz for bits? Would make a great door stop/paperweight.

[pinkmouse]

Well, the first thing I would do is open it up and disconnect the pcb from the psu. If it powers up then, you know you have a fault on the main amp board. If not then the fault is with the caps or the bridge, both of which should be relatively easy to fix.

If the fault is with the pcb, then you have an alternative option. Measure the voltage across the caps, and if it is less than about 30V on each rail, you could just strip out all the old amp boards, and stick in a couple of BrianGTs gainclone boards.

Or you could just send it to me!

[Nuuk]

I agree with Al. If you can't locate the fault, and the PSU voltages are suitable, make a Gainclone out of it.

This is within the capabilities of a beginner and you can see an example of this sort of project here .

[Jimlondon]

Hmmmm, interesting.
Thanks again for the thoughts.
I've done as Al suggests, unplugged the PSU from the PCB & for the first time in some weeks I have not been greeted by a popping fuse as soon as I turned the power on.
I am getting just over 29v out of the psu leads so I guess I should read up on gainclones!
Can anybody recommend any other quick checks I could do on the amp board before I bin it?
Thanks.
Jim.

[pinkmouse]

Apart from checking for any obviously burnt or boken components, nothing without unsoldering components and checking them individually.