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Transformer Diagnostic.

Eureka!! D8 was bad... Now I got 13V at pin16... Selection switch AM/FM/Aux etc... light up... continue to check for the rest... Big thanks Merlynski.
 
Plug the unit thru DBT, and playing CD via Aux sound so good. Got excited and plug directly to the socket. Power it up, nothing.. smoked the R3, 910R/2W between pin25 and 27 and I think the R2 went out too. May be the D10 and D11 went bad too. I don't have any 910R/2W nor any replacement for the 23V zener for D10, D11. So this will be another day... So close...
 
MyLastWord said:
Plug the unit thru DBT, and playing CD via Aux sound so good. Got excited and plug directly to the socket. Power it up, nothing.. smoked the R3, 910R/2W between pin25 and 27 and I think the R2 went out too. May be the D10 and D11 went bad too. I don't have any 910R/2W nor any replacement for the 23V zener for D10, D11. So this will be another day... So close...
Click to expand...
Don't try to play music on DBT, circuits will not have correct voltages. When you get those parts replaced bring it up on DBT, check power supply voltages are present and probably low but reasonably balanced. Check and set DC offset on power amps, check idle current (Bias) for adjustability then reduce it to minimum. With volume minimized and no input bring it up on full power and check every power supply voltage, recheck DC offset. Then set idle current (bias) per Service Manual. Then try music, bringing up volume slowly, play at low level for a while. Reduce volume, remove input, recheck bias and dc offset. If they are still good try music again at a bit higher level. Repeat checks after unit has warmed up for a bit. Tomorrow is another day !
 
Turn out Q6 keep smoking and D8 14v Zener keep going bad... not sure which cause which... So I got the replacement for D10, D11 (22V Zener though) put it in and visual check and replaced Q6 C945 and D8 (smoked. I think from the last time, not the 910R/2W resistors).. put it though the DBT and measure voltage all around and everything within spec.. Relay kick-in.. panel indicator lighted up.. So far so good. Go thru the manual to do Center Voltage adjustment to get it close to 0V (+/- tens of mV, don't think my DMM that good) . Adjust idle current around 30mv and everything still OK if connected to DBT.
At this point I think it's ready. Trying to plug thru normal outlet, with nothing connected to the unit, immediately the Q6 start to smoke so I turn off immediately.
 
Have you replaced Q5? Pull Q5 and Q6, then check the voltage on the plus side of C13 for +24vdc. Test Q5. Measure R9 for 10Ω.
 
Q1, Q5 2SD712 was replace with KSC2073 awhile back but I think they are OK, hasn't change since. Q6 kept smoking and just replaced (3rd time now) along with D8. R9 checked around 10Ohm. Qe5=Pin16=12.8V, Qb5=Qe6=13.5V, Q6b=14.2V.
 
Recheck voltage around:
p20 +31v(* spec say 33V), p22 +46v(* spec say 50V), p23 +22.8v, p25 -23v, p27 -50v, p28 -12.8v, p16 +12.9v, p18 8v.
Beside p20 and p22 (a bit low) everything else seem within spec..scratch my head, pulling my hair...
 
Q2 went bad, has to replace again with last KSC2383....Now they are power up without DBT OK, lights up... protection click in... so far so good...:):banana::jump:
 
Good deal! I was looking and pondering why D8 was dying, at first it seemed like Q6, but after the third time it was time to look elsewhere . . .:bigok:
 
Not sure if this is still relevant, but you previously said Q6 kept burning up? If you are using KSC945, verify basing with a meter. The original 2sc945 is a collector in the center lead, like most Japanese small signal transistors. If you ordered KSC945, the base lead is in the center, and will burn up as soon as installed. If you ordered KSC945C, the collector will be in the center and will go in the same as the originals. My thought was maybe you had some KSC945, and circuit worked when you put back in a 2sc945 or ksc945C. Glad to see you got it working..
 
sregor, you are right, I have a mix bag of 2SC945 and KSC945 and wasn't aware of the pin out different. The 3rd time I picked KSC945 and got it right by luck. Will be careful next time.
However, after fixed Q2, adjust the idle and offset, holycrap this receiver sound ever sweet, fantastic. Thank you everyone for help-out.
 
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