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Akai AA-5500 Fuse Question

Ok, I checked all the resistors on the right channel board and they all look fine, and I did the transistors on both boards (I'll try and do the other resistors later). TR1 (2SC900) and TR3 (2SC959) on both boards seem to have failed, so I suppose I should desolder them and check them out of circuit. Could these explain the high DC and fuse failure? I'll also try and remove the output transistors that tested fine before to make sure they're ok out of circuit too
 
yes they could well explain things .. i find it odd both sides are playing up in the same way . are the transistors failed short ? as in zero ohms between 2 pins .
and good idea to check the outputs again .
 
These are the values for the ones that looked bad, only one of them has a short indicated, the rest just look like they have conduction where they shouldn't. I assume the values are in mV; I used the diode function on my DMM rather than ohms. '1' I'm presuming means no conduction.

EYDKm.jpg
 
not sure of your readings to be honest ...way i do it is one lead on base then other lead on collector then on emitter .. depends on whether npn or pnp which lead goes on base ..try both ways anyway ..one way should read around 600 other way should read zero .
i don't know how your meter reads they can vary a little .
anyway a suspected short will show as low ohms on 200 ohm setting .if your meter has beep test it will beep .
just thought simple way to see what short shows on diode test on your meter is set to diode test and touch probes together .
 
I tested them according to this thread, placing the leads in the combinations shown in my table above; I switched the polarities for the PNP transistors which I should have indicated. My meter has a beep test and beeped on the one short I put in the table, all the others just had readings that looked wrong according to that thread (but no beeping).

The other resistors on the boards (T2 and T4) read ok according to that thread so I didn't post the results.

My meter's diode test shows 002 when the leads are touched, and it showed that when it beeped on that shorted transistor. However I retested it today the same way (positive on collector to negative on base) and it now shows about 750 like the other one!
 
do you have hfe test on your meter ?
if not no problem . looks maybe safe bet to get new transistors anyway .
will be better and cheaper to find more modern substitutes for t1 and t3 .
 
might be as well to start a new thread for the replacements . plenty of people will advise
the originals look to be silly money .
 
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