Kenwood -Trio dual power supply issue

[diepbtt]

Measuring some points on the power amps as the schematics shows i get following:
Left power amp x07-1440-01
at De1 (+24V) + 22.8V
at De2 (-14V) -13.7V
at R9 ( +61V) + 51.4V
at R10 ( +61V) + 51.3V
at R11 (+10V) + 8.9V
at R12 (+1V) + 0.9 V
at R13 (+60.9V) + 52.6V
at R15 (+0V) + 118 mV
at R16 (-64V) -53.6V
pin 2 (1.35V) +1.25V
pin 6 (+ 12mV) +120mV
pin 8 (+0.6V) -0.41V
pin 10 (-65V) -55.6V
pin 13 +0.1V
pin 15 (+65V) + 55.6V

Right power amp x07-1440-00
at De1 (+24V) + 23.3V
at De2 (-14V) -13.7V
at R9 ( +61V) + 51.9V
at R10 ( +61V) + 51.9V
at R11 (+10V) + 9.8V
at R12 (+1V) + 1.15 V
at R13 (+60.9V) + 52.3V
at R15 (+0V) + 35.8 mV
at R16 (-64V) -54 V
pin 2 (1.35V) +1.2V
pin 6 (+ 12mV) +36.9 mV
pin 8 (+0.6V) -0.54 V
pin10 (-65V) -55.6V
pin 13 +0.1V
pin 15 (+65V) + 55.6V

All power transsitor 2SA747A/2\SC1116A with diode test out of circuit are fine, no short.

The only difference of the power amp boards of TRIO KA9300 vs Kenwood model 600:
VR2 1K by KA9300, VR2 =500Ohm by Kenwood Modol 600

Does it say anything what may be wrong?

 

[diepbtt]

on the TONE, PRE and FILTER boards i also get:
TONE
pin4 +29V
pin 8 -28.8V
pin10 -28.8V
pin 14 +29V
pin 19 -41V
pin 23 -41V

PRE
pin 14 +28.8V
pin 15 -27.8V
pin16 -28.6V

FILTER
pin 13 +29v
Pin 14 +29.1v
pin 15 -28.2V
pin16 +28.3V
pin17 + 28.8V
pin 18 -28.6V

 

[diepbtt]

When i mounted all the power tranies to the heat sinks as i reference it with amp8.com - you suggested exactly - the DBT lights showing i have shorts with reading B+/- of boths sides 26V somewhere.

Dis-mounting the tranies from one channel no improment but with big suprise the channel without power tranies does have B+/- 26 V.

Dis-mounting all power transitors of both channel the relay clicks and i get above mentioned readings while connection with DBT 100W.

I am not aware taking such measures when the DBT lights relative strong

Hop now you understand the situation

 

[diepbtt]

Can i measure the voltages like above with all power transistors mounted under these situation( with DBT 100W, B+/- 26V) ? I ask so because for the checking it takes some time it can destroy the power transformer/power transsitors?

I will re- check the wirings but until now i do not find any mistake as i follow the wiring diagram for the power transistor of this Trio KA-9300 i can get it only from a japanese yahoo blog

Thank you

 

[diepbtt]

Do not understand what you mean.
I always say both amops Trio KA-9300 and Kenwood model 600 are almost the same excerpt some minor changes . They share the same power amp circuit. So i can use the power amp diagram of kenwood model 600 or trio Ka-9300 without any problem for checking the component connection whether it is correct or not. Until now i do not find any mistake here.

 

[gort69]

Other than the crackling sound did this thing work before you replaced Qe1,2 and 5? If that's all you did and now it doesn't work that's where I'd be looking.

 

[diepbtt]

Yes before i try to replace Qe1/2 and Que5 it works normally , just with loud cracking noise from one channel. I just did it, no further replacement.

After this work i DB tested it and it is OK the relay clicks, i plugged it directly to the main, can adjust Offset of both channel to 4-5mV, just at one channel i get no bias( zero).
I then took out the board with zero bias again to checked, replaced with the new ZTX694B for sure, then i tried DB testing and stuck with that as mentioned.

By the another Trio KA-9300 i encountered the same problem - very loud cracking sound as it can destroy the speakers soon - i also try to replace Qe1/2 & Qe5 but by this one i also did replaced some transistors, ceramic caps in Tone amp, Filter, re-wiring for some wires broken.
DT testing it after repacement: again that same issue - the DBT lamp gets bright , dimms not much. it mean i made mistake again as i measure B+/- both power amp boards: AGAIN 25V

But i can not be sure whether the problem is caused from power amp or from these boards(Tone/Filter). But i let correct it later as i can find the cause of the first one

So summerising both Trio KA-9300 with same problem!

Maybe possible i may make mistake by re-wiring several broken wires it can occur every where as it is 42 years old. Nevertheless i like the hapstics to use it though soundwise i prefer Trio KA-9900 aka Kenwood KA-907 and L-07C/M over it.

 

[gort69]

Read this thread. EchoWars is THE expert on these. Pay particular attention to post #2. Qe3,4 & 6 are the known trouble makers, not Qe1,2 & 5. http://www.audiokarma.org/forums/index.php?threads/600-supreme-bias-drifting.564806/#post-7408936

 

[diepbtt]

Thank you for your input.

Before i do this current repair i had replaced all Qe3/4, and 6 with Sanyo 2SA1507T/2SC3902T, all new VRs and Qe11/12 with Toshiba 2SA1837/2SC4893, even all Qe7,8,9,10 2SA673A/2SC1213A with KSA1013/KSD1616, De 1/2 zener diodes already and it runs fine.

This time i also re- checked it in circuit with DMM diode test they are still OK.

 

[diepbtt]

Sir, when i measured voltage rails B+/- i get +/25V on the both sides under the conditions: with

mounting power transistors on one channel or both (and in serie witth DBT).

Without any power transistors mounted i get B+/- about 54-55V as noted clearly above.

Do you understand now my main question:
Why the B+/- of the channel without any power transistors drop also?


OK the above readings do not tell much without power transsitors mounted but i think it may
tell me all other components on the power amp boards are OK with their functions?

 

[diepbtt]

Update: Finally i found the cause of both Trio KA9300 aka Kenwood model 600 encountered same problem Q5 2sc1681, i had replaced with 2SC945, then KSC1845, even ztx694B all are not suitable for the purpose. After seeking all other possibilities, re- checking all components etc without success i go back to use the old one 2SC1681 they work again piece after pieces. Hey these amp boards are very sensitive with the Bias transistor Q5, never imaging that before that takes me almost 2 years investigating such odd problem!

 

[gort69]

Yeah boy - Qe5. That's one that's best left alone unless it is faulty. It was faulty on my 650 - a 2sc2240GR worked w/o making any other changes. YMMV - just ask @rjsalvi