Kenwood KA 9100 power supply tips.

anderslober

anderslober

Yikes...not again!
I have a nice KA-9100 on the bench at the moment.

Is there anything special that needs changing on the power supply? Capacitors will of course be changed..............................are there any 'over-driven' tr's or diodes?

Thanks,
 
I only replaced the capacitors and the relay on the power supply board. I've seen Japanese websites where they replace the glass diodes (they call them dame diodes) with modern equivalents.

I found a lot of cold solder joints and just bad soldering altogether. If you compare the KA 7100 and the KA 9100, you notice that the 7100 boards used a more modern process than the 9100 (Probably since they made a lot more of the 7100) and the 7100 had perfect soldering. Some of the boards had an amazing amount of flux to be removed.

The preamp was a pain to disassemble and reassemble. I had to do it three times (lost the left channel because a wire came loose) and found that it was easier to remove if you disassembled the facia from left to right (can probably do this in my sleep now).

After recapping, cleaning switches and diagnosing the fault (I created) I will note that this is a great sounding amp for my Cornwall IIs and it's been in service since May (knocked the CA 2010 and AU 717 from rotation, maybe the 9900A will knock this one off once I set the bias). Phono section is very quiet, which is what I prefer (no coloration).
 
Ok...that sounds good. I have already done the pre-amp......yes, there was quite a few places where the solder looked suspect. 2 caps where definitely barely hangin' on to the board. I re-soldered nearly the whole board after going over it with a loop.

On the power supply, I may change the w06b's to 1N4005's.

Any other good advice would be appreciated......thanks.
 
Should I change any tr's or diodes on the amp boards? 2sc1885, 2sa912.......?

I just want to make the amp as 'stable' as possible.

Thanks.
 
Ok...the unit is fully recapped(yes....diode board too!). I DBT'ed the unit...all fine....normal power...all fine....set dc off-set too. All good. I then proceeded to sound test.....only sound in left channel.....I swapped the pre-out/main-in and sound moved to right speaker...PHEW!.....amplifiers ok.

Now I just need to find the fault in the pre-amp.......are there any particular suspected suspects? Tr's?.......

All switches are clean.

An observation(maybe a clue)...when I push the high filter button in ...the right meter rises a few mm's.

Thanks.
 
Check the wiring on the two boards on the left side of the preamp. On mine some of them were quite loose and one failed during the recap (which is why I lost the left channel on the phono stage).
 
Ok...I will check the wires. With the volume way up, I can hear the signal slightly in the right channel. So there is a little bit of signal getting through..................

I changed the four 2sa640 's(on the pre-amp) to ksa992's.

How about the 2sk68 fets....are they problematic?
 
I checked the wires...all are ok. I then started to measure voltages at the tr's. Quite a nerve wracking experience with the whole facia disassembled!

All tr's measured good.

At the small L/R output connector....the scat' says the LEFT should measure 1v.....mine measures 0.0v................clue?

Any ideas would be great....thanks.
 
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Man...I need help with this ka9100. I have changed the 2sk68a'a to new, all tr's except the 2sa847's have been changed. All voltages are as per scat'. I even made a continuity check from input RCA to the board....all good. Also, continuity from the board(small connector) to pre-out/main-in switch measured fine for both channels. So the signal is getting to the board for both channels...........just when leaving the board(small connector).....right channel is missing...................I don't get it.........all seems normal.

I have also checked polarity of the new caps...all are good.

I have cleaned the speaker switch, tape switches an'all.............................if a guru has an idea of what to test.....please indicate....thanks.
 
I just tried by-passing the hi/lo filter switches in the OFF position. This did not help...still no sound in right channel.

This ka9100 is putting up a good fight.

Here is what we know:

-Amplifiers are ok......tested with swap of pre-out/main-in.
-All switches cleaned multiple times. Also the 'separate/connect'-switch.
-Cap polarity checked and compared(with scat and other pic's).
-Voltages in the pre-amp are normal.
-By-passing filter switches had no effect. I think the switches are ok.
-All wiring continuity tested......all are ok....no broken wires anywhere..

I have a feeling it is a small thing and that we are close to solving the issue.

Gosh....what could it be?
 
fernarias said:
I only replaced the capacitors and the relay on the power supply board. I've seen Japanese websites where they replace the glass diodes (they call them dame diodes) with modern equivalents.

I found a lot of cold solder joints and just bad soldering altogether. If you compare the KA 7100 and the KA 9100, you notice that the 7100 boards used a more modern process than the 9100 (Probably since they made a lot more of the 7100) and the 7100 had perfect soldering. Some of the boards had an amazing amount of flux to be removed.

The preamp was a pain to disassemble and reassemble. I had to do it three times (lost the left channel because a wire came loose) and found that it was easier to remove if you disassembled the facia from left to right (can probably do this in my sleep now).

After recapping, cleaning switches and diagnosing the fault (I created) I will note that this is a great sounding amp for my Cornwall IIs and it's been in service since May (knocked the CA 2010 and AU 717 from rotation, maybe the 9900A will knock this one off once I set the bias). Phono section is very quiet, which is what I prefer (no coloration).
Click to expand...
I here you.....I picked up a 9100 last year to do a full recap.
Of all the recaps I have done...The 9100 is a PITA...It's the ONLY item I put back together and said...Not this one...Front Tone/Switch board is the PITA.

The 8100 was a breeze to work on.

I will be watching...
 
I feel that i have thoroughly checked over the pre-amp board's in's and out's. They all look good to me. Continuity is fine.

Am I looking in the right place? Diode board? Relay(was taken out and cleaned) area?
The signal passes through both...............or am I mistaken?

Edit: I guess it can't be the diode board or relay.......the right channel does work when I swap pre-out/main-in.
 
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At what point did it stop working. Was it working after you recapped the preamp only? Did it stop working after you recapped the power supply?
 
I checked the volume and balance pot......continuity tested an'all.

The unit came to me in a poor state.....'1 channel fuzzy....1 channel not working'...etc, etc........I dbt'ed before I started to re-cap. No major shorts. After (full)re-capping, 1 channel is fine(left)......right channel still not working.

I am tracing the right signal from input to output.............the signal is definitely getting to the board....just not 'out' of the board.......some friggin' resistor or cap is 'blocking' it..........all tr's have been changed....except the 2sa847's. They can be bypassed with tone defeat, so I don't think it is any of them.

I have looked at the block diagram....the signal sure does pass through a lot of stuff before come to the board...............

On the scat......there is a HIGHLIGHTED black line......I am guessing this is the signal path. Can someone confirm...thanks.
 
yes thick line is signal path ...
did you clean normal separate switch ?
i think the 1v you mentioned earlier is max 1v signal .
have you tried switching to mono and stereo reverse ?
 
I have cleaned all switches several times.....especially the separate/normal switch. They are squeaky clean and dripping with deoxit. I have tried mono/stereo multiple-many times.
It is really strange this..............the black signal line is easy to follow once all tone- and filter-controls are bypassed........not much in the way to block the signal............

I have also checked my cd-player and cable.....all is ok.

All the wiring is also intact........I have also re-soldered the whole board. I have gone over the board with a loop many times.....all looks ok.

This has to be something silly...........................the right amp works fine....tested with another pre-amp.
 
Well......I guess it had to happen at some point. For the first time, I may have to give up on an amp. I just don't know where to go from here on this unit.....................I have tested the amp exhaustively today....electrically, all is ok....re-soldered.....deoxited beyond reason...........
 
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