:'( please help

[sparky68]

hey guys
Ive fried my amps Musical Fidelity MA65 Monobloks,
I recapped them including the PS caps, i put them on polarity correct i think. all the minus's opposite the plus sign on the board, also the PS caps are on the right way round as indicated from the markings on the board.
Now this applies to both amps so rules out a bad soldering job i assume ?
here is a pic with which burns within seconds of powering up

nothing else gets hot ?

please help
Mark

[QSerraTico_Tico]

Correct voltage rating of new caps?

[sparky68]

hi
ive replaced the small signal caps with 100v the old ones where 63v ?
the PS caps ive replaced with the same as old ones 63v ?

[DF96]

Something in the amp is shorting, or nearly so. You have probably disturbed something during your recapping, maybe output bias? Remember, introducing faults with a hot soldering iron is as easy as fixing faults which is why the best policy is only to fix the things which are broken - then you tip the statistics in your favour.

[sparky68]

thanks DF96
but could i have done this to both ? that is what im finding difficult to get my head round,
This is my first attempt at soldering i agree but to be honest it wasnt to hard a job.

Mark

[AndrewT]

Hi,
power up using a mains light bulb tester in between the mains socket outlet and the amplifier plug top.

The bulb will light up, confirming that the amp is trying to draw significant power.
A few AC volts will be fed to the mains transformer and give just sufficient secondary voltage output to allow the circuits to charge up (very slightly).
You can then check/measure the polarity of the PSU and the smoothing caps and any other suspect voltages.
Don't try measuring output offset and output bias current in this ultra-low voltage test.

BTW,
your thread title is uninformative!

[jaycee]

Have you tried to run this amp with the lid off ? If so, you have fried the output transistors. The lid is the heatsink and the amp will quickly fail without it.

The amp is basically the power amplifier stage of the MF A1 amplifier, with both channels wired in parallel. It is, IMO, a dreadful design prone to failure.

You must have installed the capacitors the right way - if you reversed them and powered up, they would have exploded.

[DF96]

Good soldering takes a bit of practice, like most skills. Do you know how to recognise a dry joint, and correct it? Have you bridged any tracks?

[sparky68]

Thanks for all your replys fellas, sorry i havent been back to the thread as its all been bit of a nightmare and been on nightshifts,
They are now in safe hands being cared for by a v.kind friend so fingers crossed they'll be back up and running soon with all new caps
be interesting to know what i did wrong apart from taking a soldering iron to them.
thank guys
Mark