Kenwood -Trio dual power supply issue

[diepbtt]

Hi all,

My 2 Trio KA-9300 aka Kenwood model 600 have issues with very loud crackling sound therefore i tried to replace the 2. differential transitor pair Qe1/Qe2 2SC1400U with ZXT694B( modified the pin layout C-B-E to E-C-B) in the Power amps metal box and Qe5 2SC1681(GR) with KSC945C(modified pin layout) , then i powered it up with DBT 100W the lamp gets bright, so i measured the voltage rails of both channels with the result B+/- 26V, even without Power supply B.

It means i have some shorts i must find out and solve.

OK i first take out two pairs of 2SA747A/2SC1116A of the left power amp channel then measure again the voltage rails (still with DBT) i still get B+/- 26V on both power amp channels.

Further i take out also other two pair 2SA747A/2SC1116A of the right power amp channel, now the relay clicks and i get the readings B+/- of both channel 56,4V.

If i as trying re-install the two pair 2SA747A/2SC1116A to the left power amp channel , i get B+/- 26V on the left power amp channel again, but to me i can not explain myself why i also get B+/- 26V on the right power amp channel without any power transsitors 2SA747A/2SC1116A installed while this amp is designed with Dual power supply? How can it be?

In addition i have checked all wirings, transitors, diode, resitors, their orientation etc on the both power amps and do not find any mistake i may make.

Could someone help me pointing out the possible causes of such issue as that problem occur the same issues on the both amps.

Thank you

 

[diepbtt]

puzzler that, or not, one pair of transistors are shot, the supply is low on both ch because of the volt drop across the lamp, maybe

Thank you for your input.
I already have taken out all Power transistors out and checked with DMM thay are all fine.

They can also not shot because before i tried to repair it it works but with loud crackling sound even i had re-capped, replaced all bi polar transistors in Tone/Filter circuit as well as zener diode & 2SA810/2SC1451 with 2SA1507T/2SC3902T in the power amps.

After differential transistors... replacement this time i always checked it with DBT, no magic smoking by power up checking.

This Trio KA-9300 aslo does not used power indicator lamp7.5 V, but a red led.

Right it is very puzzle for me as Dual mono power supply are they not absolutely independent or i make serious mistakes?

For your informations:
Trio KA-9300 as japanese model has some minor changes from Kenwood Supreme model 600:
Toroidal PT
Muting board with small relay
no 500mA fuse
led indicator lamp
in Tone control & Filter circuit they used also bi-polar transistor, not all FET
in Power amp Qe5 is 2SC1681(GR) instead of 2SC1746
No present switch
.....
See some pictures of it i take from amp8.com for my illustration purposes

 

[DrumminDaddy]

Do you have the schematic?

 

[diepbtt]

No, but the pre amp, tone control, filter circuit are almost the same with some minor changes

 

[diepbtt]

Even the power amps are the same as i compared the components with the schematics of kenwood model 600 with excerption Qe5 2sc1681(GR) instead of 2sc1746(GR)

Power supply deliver B+/- 65V just with toroidal transformer instead of regular ones in kenwood model 600 when it was OK.

 

[diepbtt]

take out pin 10 & 15 of both power amp boards i get the readings B+/- about 66 V of both sides.

 

[DrumminDaddy]

If these pics are from your unit and you'd taken all the wire wraps off those boards and rewired them, you'll need a schematic because it sounds like a wire(s) is crossed...

Looks like he pulled the pics from here;
http://amp8.com/tr-amp/trio/ka9300-2.htm

 

[diepbtt]

Looks like he pulled the pics from here;
http://amp8.com/tr-amp/trio/ka9300-2.htm

Yes because i want to tell you that(TRIO KA9300) is almost the same of kenwood Model 600. I also noted that i taken the pictures from amp8.com for my illustration purposes as noted above, not from my one because i need a digital camera

 

[diepbtt]

If these pics are from your unit and you'd taken all the wire wraps off those boards and rewired them, you'll need a schematic because it sounds like a wire(s) is crossed. Also, just because a transistor checks out on the DMM doesn't automatically mean it's also good under load.

When i pulled out the power amp boards for checking, some of them are broken i then soldered it directly, no wraps re-wiring. Inside cosmetics are not important for me.

I have checked all wirings from 1 to 15 of each power amp several times, no (cross-)shorts.

Wirings, circuits of both power amp are exactly like ones of Kenwod model 600, even all components on it are the same excerpt Qe5:KA9300 2sc1681(GR), Model 600 2sc1746(GR)
So i can use kenwood model 600 schematics, at least for power amp sections for my checking.

OK maybe there are still bad transistors causing shorts on one power amp channel with (Power transisitor ) but why the B +/- of other power amp channel(without Power transisitor decrease at same level ? But this amp was designed with dual mono power supply? That is my main question!

 

[gort69]

Did you make note of the fact that the originals for Qe3,4 & 6 are center-base and that you replacements are center-collector?

 

[diepbtt]

Did you make note of the fact that the originals for Qe3,4 & 6 are center-base and that you replacements are center-collector?

Yes i already have replaced these transistors long time ago and it works perfectly before it has issue with loud crackling sounds

 

[diepbtt]

Post now some pictures of my 2. KA9300

 

[diepbtt]

left power amp x07-1440-01

 

[diepbtt]

right power amp R x-07-14409 -00

 

[diepbtt]

adding some more pictures

 

[diepbtt]

why all the pictures, did you get a camera for xmas ?

I just want to show the similarities of this Trio KA9300 ( dual mono power supply design, same power amp board etc.) with Kenwood model 600 so maybe someone knowing the Kenwood model 600 can help me sorting it out(wiring connections, component orientation...)
If it bothers you then ignore to see it.

 

[diepbtt]

i would see if some repairer will fix it for you !

Thanks for your help but i live very far away from United states so it is not economical for transport etc.
But i may find out the cause of that problem as i remembered by repairing it sometime when i took a wire ( do not recall which one) the relay clicks, then re-cheched it again but now DBT lights.

Does It means i may have "soft" shorts by a AC wire with the chassis it causes the issue B+/- of both power amps decreasing even one channel without power transistor pairs ???

 

[diepbtt]

I ú

 

[diepbtt]

I use the schematics from Kenwood model 600 to meassure some readings(with DBT 100W, without any power transistors, the relay clicks)
Power supply A
pin 1 44.4VAC
pin 2 - 55.3V
pin 3 44.4VAC
pin 4 + 55.2V
pin 5 not use
pin 6 not use
pin 7 0V
pin 8 0V
pin 9 0V
pin 10 + 0.1V
pin 11 + 0.1V
pin 12 + 0.1V
pin 13 + 0.6V
pin14 + 55V
pin 15 44.2VAC
pin16 -55.1V
pin 17 44.2VAC

Power supply B
pin 1 + 29V
pin 2 +55.4V
pin 3 -28.8V
pin 4 -41.3V
pin 5 - 55.4V
pin 6 + 0.6V
pin 7 + 0V(GND)
pin 8 +0.1V
pin 9 0V
pin 10 -6.6V(to head phone jack)
pin 11 +27V
pin 12 +1.1V
pin 13 -55.6V
pin 14 -28.4V
pin 15 - 40.9V
pin 16 0V
pin 17 +56V
pin 18 + 28.7V

 

[diepbtt]

Further reading under same conditions above
Left power amp X07-1440-01
pin 1 + 0.07V
pin2 +1.2V
pin 3 0V(signal GND)
pin 4 0V(signal in)
pin 5 +0.4V
pin 6 + 0.1V
pin7 0V(GND)
pin 8 + 0.5V
pin 9 +0.5V
pin 10 -55.9V
pin 11 +0.5V
pin 12 +0.5V
pin 13 0V
pin 14 0V
pin 15 +56V

Right power amp X07-1440-00
pin 1 + 0.07V
pin2 +1.2V
pin 3 0V(signal GND)
pin 4 0V(signal in)
pin 5 +0.1V
pin 6 + 0.1V
pin7 0V(GND)
pin 8 + 0.4V
pin 9 +0.4V
pin 10 -55.7V
pin 11 +0.6V
pin 12 +0.6V
pin 13 0.1V
pin 14 0.1V
pin 15 +55.7V