MOSFETs/Endstufe defekt Hilfe!

1) Ja
2) Auch Ja.

But, P-L-E-A-S-E !!! If you want any helpfull answers give information about the Brand and Typeno. Probably a schematic diagram or a Service-Manual is available (...or even on hand, I have a lot!) and studying the schematics will give clues to what happened and how it should be fixed.


Kind regards,

/tri-comp

Hi,
the brand is MERACUS, and the type is INTRARE (1st version). Sadly I haven´t any kind of schematics nor diagram on hand.
Thanks and kind regards

Hi,

I don't have the schematics or any other information on the amplifier.
Still, it must be build according to some common rules.
At least one channel (Right) is working and could be used as a reference for repairing the other.
I would start by removing the MOS output transistors (all of them, not just what you may measure being shorted out) from the defective channel. Remember to take notice of what-went-where if the transistors are not of the same type which is unlikely. Check the removed transistors for shorts and you should find some as the fuses blow instantly. The driver-transistors and probably some surrounding resistors (Gate-resistor for example) may be burned even if you don't see it. Measure across them with an ohm-meter and compare with the right channel. Don't remove right channel MOS transistors, they won't disturb your measurements.
What are the typeno.'s of your MOS transistors?
In my opinion, when you repair a MOS-output amplifier, the original or VERY close to original transistors should be used for replacements. ALL MOS transistors should be replaced even if some doesn't appear to be defective. If the previous repair company didn't do it, you may now see the result.
Also be aware that some replacement parts are pirate-parts manufactured in the far east (China). They do NOT come close to the original specifications for the MOS transistors and will blow in a short while. It's not easy to spot the pirated parts, even well known parts suppliers like ASWO have them, unknowningly I'm sure. I recently had problems with ST parts (SGS-Thomson) from ASWO. When I OPENED the defective power-transistors (TO-3 case, just remove top in a wise) they were rusty inside and the size of the transistor was way too small. They lasted only for a few hours in the amplifier. When ASWO later supplied the original ST-transistors, the amplifier was repaired, nothing else was wrong and it still runs 4 months later.

You COULD insert 1A-F fuses the first time you power-up the amplifier after repair. It should give your MOS-transistors some protection in case more parts are defective. (...I hope ) When all's good replace with 3,15A-F fuses.

One VERY strange thing. HOW can your headphones play in stereo when one channel is dead? ...and it IS when the fuses blow!
Probably the amplifier has a separate output amplifier circuit to drive the headphones (not likely) OR your amplifier has more than one fault (very likely)

Kind regards,

/tri-comp

EDIT: Spelling errors

Hi, thank you for your very kind help, this ansnwers all of my questions! Yes, the amplifier has a separate circuit for the headphones I think. The problem that I have now, is how to get the ORIGINAL mosfets?????
With kind regards.

In my opinion, when you repair a MOS-output amplifier, the original or VERY close to original transistors should be used for replacements. ALL MOS transistors should be replaced even if some doesn't appear to be defective. If the previous repair company didn't do it, you may now see the result. Also be aware that some replacement parts are pirate-parts manufactured in the far east (China). They do NOT come close to the original specifications for the MOS transistors and will blow in a short while. It's not easy to spot the pirated parts, even well known parts suppliers like ASWO have them, unknowningly I'm sure. I recently had problems with ST parts (SGS-Thomson) from ASWO. When I OPENED the defective power-transistors (TO-3 case, just remove top in a wise) they were rusty inside and the size of the transistor was way too small. They lasted only for a few hours in the amplifier. When ASWO later supplied the original ST-transistors, the amplifier was repaired, nothing else was wrong and it still runs 4 months later.

...dem kann ich nur zustimmen

Ich habe vor Jahren mal einen Meracus intrare repariert, soweit ich mich erinnere, waren da bipolare Transistoren, also keine Mosfets in der Endstufe.
Die oben genannte MJE - Typenbezeichnung würde auch eher auf normale Motorola/ON-semi Typen hinweisen.

Gruß, Helmut