Kenwood KA 9100 power supply tips.

[petehall347]

check all grounds .
if ok then maybe it would be a good idea to get voltages at the output chips .
will read over the read later . i have a busy day ahead .storm force winds apparently on the way . i have lots of stuff to move outdoors . a marquee for one .

 

[anderslober]

Pete......take a look at SM page 19. LEFT amp.....pin7......connects to pin5 of IC....why does it say 26.8v/8ohm?.........pin5 of the IC is 0v.

 

[Duffalora]

You may have more than one issue here but let's try and isolate. Have you checked the voltages on the power supply/relay board? If they are good, can you then absolutely confirm that the power amp is working perfectly. Easiest way is to seperate pre and power, connect an ipod directly into the power amp (with the volume on the ipod turned right down), then play a few tracks and make sure both channels sound the same.
BTW, have you de-oxited the pre/power switch?

 

[petehall347]

the voltages in the square boxes are what i believe to be maximum RMS voltages AC . no signal no voltage .

 

[anderslober]

I hooked up an Onkyo A5 pre-amp section to the ka9100 amp section. No speakers connected.

The ka9100 remained ON, with meters hooked up to left/right dc-offset terminals.

With Onkyo ON....first picture..........left=1.39mV......RIGHT=386mV.
With Onkyo OFF....second picture....left=101mV........right=2.751V.

Protection relay clicked ok.

This to me does not follow logic at all.

 

[anderslober]

I connected speakers to the ka9100 and used the Onkyo A5 as pre-amp......good sound in both channels. Left indicates about 0v........right channel indicates about 1.3v.....

Its gotta be a problem in the ka9100-pre-amp..................I just can't fathom WHERE...........:-(

Anybody out there with a parts unit?

 

[petehall347]

how can it be the preamp ? you are using a different one . and still problems .. it surely has to be the main amp at fault .. maybe its a bad earth or a capacitor or resistor that connects to ground . might even be a flaky diff transistor . or a solder joint or cracked trace .

have you tried AC voltage at speaker terminals instead of dc ? am wondering if it is really an AC voltage from oscillation ..

did you check offset with and without speakers connected ?

 

[anderslober]

Pete.....it is not at all the same situation with the A5 connected. When using the A5 the ka9100 amps work fine. So it must be a ka9100-preamp problem, as there is no sound in the right channel. Both ka9100 amps are totally re-tr'ed and re-capped.

I will check AC at the speaker terminals.
Dc-offset was set without speakers connected. I just connected speakers to make sure the ka9100 amps actually worked.

 

[anderslober]

AC at both terminals is 0V.

 

[petehall347]

but you are saying there is 1.3v offset when using the a5 .and also 2.751 volts ...i think it should really be in protect with those voltages ..

 

[dr*audio]

Sorry to be jumping in here late. Please confirm the DC offset voltages at the outputs with the A5 preamp connected. Do you mean 1.3V or 1.3mV?

 

[Duffalora]

Yes, those voltages are a little confusing so can you confirm please.

Regardless, at least you have an amp that (1) is working, (2) comes out of protection, and (3) the power amp is working on both channels.

Although this is probably a redundant test, can you connect the Kenwood pre-amp to the Onkyo power and confirm that right channel is not working.


Also, have you read any of the other threads where 9100 owners have had similar problems:

http://www.audiokarma.org/forums/showthread.php?t=315454

 

[anderslober]

I have read all the threads I could find on the ka9100.

Earlier in the thread, I did test the ka9100 pre-amp with the A5 amp.........no right channel. So, I am 99% certain it is a small sniggle somewhere in the ka9100 pre-amp.

Now.......the voltages that I am measuring is the perplexing part. On the right channel, I have such high voltages, that the unit should be in protect.......but the relay clicks on fine. And the amps work with the A5 pre-amp.

I will try to mitigate the confusion a bit. We will start over.............

Dr.audio.....I will measure and re-confirm the dc-voltages at pin3/7 and pin4/8 on the amp boards. A5 connected as pre-amp. No speakers connected.

A5....ON. KA9100...ON. Left meter(pin3/7)...starts at about 50mV...decreases to 5mV...easily adjustable with the Vr. Right meter(pin4/8)...starts at about -1.6V and decreases slowly through 0V and goes to 0.4V......it is not steady like the left. The right Vr is ultra sensitive....just touching it will make the dc jump.

Now....when I turn OFF just the A5....left voltage goes to a steady 99mV......right voltage goes to 2.7V. WHAT does this mean?

Both ka9100 amp channels confirmed to be working. A5 pre-amp is ok. A5 amps are ok. Ka9100 pre-amp has no right channel.

 

[dr*audio]

Leave the A5 disconnected and measure the DC offset at the speaker terminals of the 9100.

 

[anderslober]

Everything disconnected. Measurements made at speaker terminals.

The RIGHT Vr was at its minimum possible setting for all measurements. The LEFT Vr was at spec.

Unit set to SEPARATE:
At turn ON.
LEFT : 6.7mV---->5min---->22mV.
RIGHT : -1.3V------>5min----->-241mV.

Unit switched directly to NORMAL:

Voltages 'jump' to:

LEFT: 103mV---->3min----->102mV(seems steady).
RIGHT: -2.46V---->3min----->-2.41V(seems steady).

All the above voltages are true and triple checked.

The protection clicks on fine and does not click of for both measurements.

 

[dr*audio]

To begin with, something is wrong with the protection circuit, but we will deal with that later.
Something is wrong with the right channel of the amp. I will get the schematic and have a look.

 

[dr*audio]

First check the voltage on De2 anode. It should be 24V. If so, I think ICe2 is bad. It is no longer available so you will have to make your own out of matched N channel JFETs. I can check for the part numbers but probably not till tomorrow evening.

 

[anderslober]

De2 anode=0.00V......De2 cathode=24.7V. De1 was similar.

I am willing to sub the uPA63H ........................any ideas which sub is best?

 

[dr*audio]

De2 anode=0.00V......De2 cathode=24.7V. De1 was similar.

I am willing to sub the uPA63H ........................any ideas which sub is best?

You need 2 transistors to replace this part. Use these:
http://www.bdent.com/2sk170gr-toshiba-audio-transistor.html
Or these:
http://www.diyaudio.com/store/parts/lsk170-to-92-jfet.html
You should buy at least 20 of them to have enough to match them. You are going to match them for Idss, that's the current they draw with the gate shorted to the source.
This shows how to match for Idss. Instead of the current meter, I put a 1K resistor in series with the Drain. You measure the voltage drop across the resistor and it gives you the Idss current in mA. In other words if you measured 2V that's 2mA. Match them as close as possible. Wear an antistatic wrist strap, and ground it. If you don't have a power supply, you can use a battery as shown. It is best to use a power supply, and ramp the voltage up to test, and ramp the voltage back to 0V before removing the transistor. You can use one of those white proto boards that have holes to plug in your parts, or make a fixture with a socket in it for the transistor.

 

[anderslober]

Do you think the uPA63H is/was my problem?