KA-9100 static in one channel

Gingahippy

Active Member
Hi, folks.

I'll begin by saying that I am not electrically gifted, but I can repair and replace if I know what I am looking for.

Anyway, I have a Kenwood KA-9100 that has a gentle static crackle with hiss in the R channel.

Here is how it behaves:

Crackling/ hiss in R channel, stays the same regardless of :
- A/B speakers
- Volume / Balance
- input connected or not
- Aux/Tape/phono input
- Only happens when speaker is connected.

- Tone control affects sound of crackle, can raise/lower treble of the static.

- Gone when Tone Defeat is ON
- Switching the switch on rear from Normal to Separate also stops it.

I understand from reading other threads this implies it is somewhere in the preamp section. I admit to not actually knowing where that is.

I have cleaned all switches and pots with DeOxit/Faderlube but will repeat this evening, including the Normal/Separate switch.

I do have a reconditioned power supply board that I got from ebay, it was a mistake purchase but since I've got it may as well use it. My question regarding that board is would it be easier to try and pull all those little spring like coils off the pins that connect the board or just to leave it connected and use the new caps to populate the existing board? I can handle a soldering iron well enough. If I can fix this problem then a basic recap is in order.
 
I'd start with a thorough pot/switch cleaning. If that doesn't fix it (it probably won't) I think you are correct in that it's probably in the control amp (X11-1410-00) Getting to those boards which are at the front of the unit on the right is a pretty invloved job - lots of disassembly required.Transistors Qi 25-28 (2sc1345) (Qi26,28 are for the R channel) jump out at me for being potential noise makers - there might be others. Hopefully hopjohn and/or rjsalvi and others look at this and offer their opinions - they know this stuff better than me.

I wouldn't worry about the power supply until you figure out the noise, and then I wouldn't swap out boards - too much work and not necessary. (It's almost always a better idea to leave the wire wraps intact and unsolder the posts from the board)
 
Last edited:
If the defeat switch stops the crackling then it greatly narrows the troubleshooting search. Your symptoms seem more like a transistor gone bad than a dirty switch, but I wouldn't rule it out entirely.

If a switch cleaning of the tone defeat switch doesn't solve your issue then I'd look at Qi8 and Qi10, both 2SA847, in the right channel of the tone circuit. Sub them with KSA992 and if that cures your ills then replace the left channel as well Qi7 and Qi9 with KSA992 to keep things balanced. The pinouts of the replacements are the same as the originals ECB. If your 9100 is like mine the bottom of the board will likely have lowercase letters e c b marked there to indicate which pin is which. If you're confused ask for further help.
 
So a second thorough cleaning had no effect, static remains the same. All behaviour is the same as before.

From the looks of it someone has been inside here before and not done the best job, some wires that look like they don't belong replacing a stripped piece off the PCB board, the wire wraps on posts soldered on in some places.

Thanks for the great info guys, I hate to admit it but I don't actually understand what Hopjohn has said, I don't speak electric and have never looked at a schematic before, although now is apparently the time to work it out. Will I be able to find what I need in the service manual and follow your instructions form there? Any chance someone could give me a laymans guide to how to find the boards and the components on the board?
 
I have to say that you've picked a real doozie to learn on. The KA-9100 is pretty challenging to work on. Just to access the board in question the entire front half of the amp forward of the heatsinks needs to be disassembled, which itself is a challenge if you've never torn one apart.

For starters, download the service manual here: http://www.vintageshifi.com/repertoire-pdf/Kenwood-5.php and look at page 16 for the control board schematic and page 17 for the location of the components on the board and see if it's something you want to try.

P1010982.JPG
 
I have no issue with tearing it down, just identifying the problem and finding specific components. I guess it's like learning to read a map. I hope. I'll be waiting until I have a block of time to try it out though.

Crackling seems to have gotten much louder and more crackly since the last cleaning.
 
It's most likely in the amp section. Q6 and Q8 (right), Q5 and Q7 (left) tend to drift and get noisy. Q11 and Q12 should also be replaced at the same time. 2SA912 should be replaced with KSA1220A, 2SC1885 should be replaced with KSC2690A.
I would also replace all of the electrolytic caps on those two boards and the DC offset trimmers while it was apart.
If you don't know electronics, it is strongly recommended to take the unit to someone who does.
 
I have no issue with tearing it down, just identifying the problem and finding specific components. I guess it's like learning to read a map. I hope. I'll be waiting until I have a block of time to try it out though.

Crackling seems to have gotten much louder and more crackly since the last cleaning.

Whatever you do, don't give this amp away or trash it. It is worth the effort to repair even if you have to pay someone to do it.

(I hope I'm not too late)
 
I'd like to second the above statement. I've taken nearly 6 months to do mine but it's worth it.

Take your time, one small step at a time. Post here as you do it..or if you do it. I'm marking this thread to help out in anyway I can.

 
Thanks for all your help. I was going to be brave but it developd a further issue (worse crackling that was not stopped with tone defeat) and so it went to a recommended guy who knows what he is doing. I recognized the quality of this thing so decided to spend what it needs. Looks like someone had been in before and done some shoddy work though. We'll see what my new guy can do.

I may well take time to recap it when it's working right. That's not a huge challenge to me. Just finicky. Diagnostics is way beyond me at this point.

I'm going to treat myself to all the needed components to redo the ESS Model 8 speakers that will go with it though. Recap crossovers, new psssive radiators, maybe new woofers according to one thread on here that found replacements better than originals. Human model 005 I believe.
 
Arr the shoddy work may be the reason why you're having issues. The transistors on the control boards from what I've read don't really have a reputation for going bad, but as highlighted above never say never I guess. Touch wood with mine.

My 9100 is all back together now and the improvement in sound after the re-cap is AMAZING! So much more detail in the music and a number of the small electrolytics tested bad. I'll be doing a report in my thread I have going right now in this section, included some test results on the caps to prove why a recap should always be done.

You won't regret doing it. Good luck and keep us updated :)
 
I found a resistor between 2 wires, not attached to the pcb in any way, a torn track on the pcb bridged with a wire and other such things. Luckily the guy doesn't charge an hourly rate so his low end isn't hurting him and the bigger projects don't bankrupt the client.
 
Hmm sounds someone tried to get through things in a rush before the 9100 fell into your hands. The bottom side of the diode boards (where the big filter caps attach to) were an absolute mess before I got to them in my unit. All fixable in both our cases. Just take patience and a steady hand.
 
I'm currently working on a Sansui AU-X1 with problems that I absolutely cannot find.

I work on it for a bit before throwing a tanty and throwing it back into the cupboard for another week or so.

If your job ever gets too much, just think that there is someone worse off that you!!

Patience and breaks are the key. Sometimes lots and lots of breaks.....

Tell you what works a charm in cases of noisy trannies is freeze spray. Just make sure you don't freeze any FETs, Im not sure how they act under freezespray. I just used it in a preamp with rows and rows of small signal trannies. I then had the issue nailed in about 10 minutes.
 
You people should start different threads on each of the units. makes reading this difficult.
Multiple people jumping in and saying oh I had this on mine and I did this to mine just is not the way to fix a unit.
I've worked on this stuff since it came out and that is no way to troubleshoot a problem.
OK, you can flame my comments now.

To the original POSTER: you should have someone qualified look at it and run a signal gen thru it
and have a scope to look at the signal as it goes thru the unit.

My .02
John
 
I thought I posted above that it is in the hands of a pro now. Things got worse and I was out of my depth. I appreciate all the input though. I was all ready to start the repairs based on what I was given here.
 
I thought I posted above that it is in the hands of a pro now. Things got worse and I was out of my depth. I appreciate all the input though. I was all ready to start the repairs based on what I was given here.
I think most wanted to help someone who was rolling up his sleeves.
However, the most important thing is to know when the task is beyond your capabilities.

I hope you get it back soon. They are definite keepers. I just bought one (waiting for it to arrive) and I am excited to get it.
 
Back
Top Bottom