Hi there freaks,
I'm having a hard time using google translate to dig through the vast of information located on mfbfreaks - if someone could point me to the right direction I would be very grateful.
Recently I've acquired set of two 532 mfb speakers, unfortunately one of them doesn't have the bass response mfb is fameous for.
The tests were done on the same input signal, both speakers play music but only one of the woofer after few seconds gets punchy, the other starts playing (after few seconds) but without energy. Cutting off esoteric audio descriptions I can say that the working woofer is having much higher Xmax than the other on the same signal.
I assume this has to do something with mfb - what should I check/replace/measure to repair this wonderful speaker? (its sound suprised me a lot!)
I would appreciate any kind of help
hi there mfb532, i would suspect the transistors in the signal path from input to the power transistors.
another thing to consider are the small electrolyte capacitors, they may have developed an too high resistance.
here's a service manual: http://www.mfbfreaks.nl/pdf/mfb/532/Service532.pd f"> http://www.mfbfreaks.nl/pdf/mfb/532/Service532.pdf
thank you Remi, after ts423 replace the bass response difference seems to be diminished/removed.
however the 532 with bass problem sounds more hissy/sandy on mid/high - I would suspect caps - what is your guess? do you advise to always make changes in both loudspeakers?
should r727 be getting that hot (skin burn hot)?
what can you say about ts424 and ts425 - they appear as bc158b on parts list, replaced with bc558b for manufacturing purposes - but I have ts424=bc558b and ts425=a852 41b (and a852 42b in fully working speaker) - any comment?
thanks
OK, I'm glad that it helped a bit.
I can't say if the hissy/sandy sound is a result of faulty capacitors, perhaps it is the mid speaker itself.
did you exchange the amplifiers already? by doing so you may find out if the origin of the hissy sound is in the amplifier or in the unit.
yes, R727 will get very hot, it is the series resistor for the lamp.
I don't directly recognise the code on TS425 like you mentioned, but i guess it is a Japanese type. normally I'd replace these type for BC types because they are often not that good any more. A common issue is the oxide on the transistor's legs, which may even short the legs.
The BC type is given in the service document.
yes, boards have been interchanged and all speakers are working ok - the source of hissy sound is board without a doubt.
I've posted here because I couldn't find any visibly malfunctioned components on board, not even oxidized legs of TS
I'm going to replace these exotic ts425 with bc558b and see what happens. caps next.
replacing two other TS in woofer section made little to no difference. btw - one of them had oxidized legs, mea culpa.
after replacing all small caps on one board there is a definitive improvement in sound quality over the "good-from-the-beginning" speaker. can anyone recommend doing also the larger caps? (330uf+)
can I cut off the lamp + series resistor (what else)? the lamp isn't lighting anyway
once again - great speaker!
