KA-9100 Phono Channel Problem

geode

geode

F4 Phantom Seat Jockey
Subscriber
Hi Guys. Well, I'm back again to give it one more try to get this nice amp 100% functional. It's been in mothballs for some years, although I take it out and play CDs on it sometime. I refurbed this amp a few years ago. Everything went well except I lost the right channel phono. I have done a lot to try and figure this out, but no go. Here is the last thread on trying to fix this. it includes voltages of the transistors on the phono board and other stuff. https://audiokarma.org/forums/index.php?threads/ka-9100-integrated-with-phono-problem.793460/
The schematic is in the linked thread, a long with all of what I have already done.
Today I was doing some continuity tests and noticed a broken wire at the input jacks. The wire is number 8 and it appears to have been connected to the the aux and tape B rec right channel. They are grounds for these jacks. Here is a picture of the broken wire. Could this be the problem? Thanks.

Edit: I mentioned at the end of my linked repair thread that it was fixed. Not the case at all. I thought it was fixed because I got movement on both meters. Come to find out after reassembling the beast I had the mono switch on. At that point I was pretty frustrated and decided to get away from it for a while. Thanks.

IMG_0001.JPG
 
Last edited:
Register to hide this ad
Well, I went ahead and soldered the broken wire back to where I think it broke off. Nothings changed, the right channel still doesn't work.Left channel has a hum. :(
 
Last edited:
DrumminDaddy said:
Only with the phono input, or in general?
Click to expand...

Hi DD thanks for dropping in. There is no hum as I verified today. Not sure why I heard hum the other day. It is all the same. Left channel phono works but right channel is dead. AUX works fine both channels. I have been probing grounds but so far all are good. I've done mono switch and got the expected result where both channels work. The reverse switch makes the left channel work. Seems to point to the preamp/phono boards. My eyes water up just thinking about pulling this a part again for about the 3rd time. Working on this amp is a real character builder :)
 
geode said:
…Seems to point to the preamp/phono boards. My eyes water up just thinking about pulling this a part again for about the 3rd time. Working on this amp is a real character builder :)
Click to expand...

Seems like you’ve got it isolated somewhat. Yeah, when I went over mine I only did the amp and diode boards. I’ve not been inclined to take the preamp section apart since it’s working fine. Maybe when I retire and have more time to fiddle. I’ve got so much other gear to play with. ;)
 
Well, I tore this amp down AGAIN. I checked the resistors and diodes again, but didn't see anything glaring except for some resistors that didn't match the values in the schematic. These discrepancies are on both channels of the board so I think they are errors in the schematic. I checked voltages on the bjt transistors again. Below is what they read. The voltages expected on the schematic are in <>

Q26 E 14.49 <10.5> C 22.67 <21> B 15.1 <11.5>
Q28 E 14.55 <10.5> C 29.32 <24> B 15.09 <11.5>
Q30 E 29.93 <28> C 0 B 30 <27.5>
Q32 E -29.66 <-28> C 0 B -29 <-27.5>

Note: Trans Q26, Q28 were changed out for KSC1845 the last time I tried to get this fixed. Q30 starts out with emitter voltage 29.93 and increase to 30.75. It seems like the voltages on Q30 are wonky. From what I've read the difference between the emitter and base should only be about .65V. This is the 2SA899 transistor. Luckily I have suitable replacements for the TO126 parts KSA1220 replaces 2SA899and KSC2690 replaces 2sc1904. I really am ready to close the book on this repair. It has only been going on and off for some years now :rolleyes:
The schematic is for the KA-9100 and 9150. What do you guys think my next move should be. The schematic can be viewed at this link post #32. https://www.audiokarma.org/forums/index.php?threads/ka-9100-phono-problem.255133/page-2 I tried to upload but the server refused because it is too big. Thanks to all who help.
 
Last edited:
I will try and upload schematic again. Hmm, works this time but this schematic is different size. Anybody care to help a hobbiest with the circuit analysis. I struggle to understand the theory. Before I pull all the transistors It would be comforting to know I'm not wasting my time by doing so, and risking further carnage.
 

Attachments

Are you 100% certain you are getting signal into the phono stage? I’d want to verify that my signal is getting through the selector switch before I beat myself up.
 
DrumminDaddy said:
Are you 100% certain you are getting signal into the phono stage? I’d want to verify that my signal is getting through the selector switch before I beat myself up.
Click to expand...

With power off...
on Q21 connecting to the drain and pin 5 for left channel, continuity test through the switch gives a 268 ohm reading.
on Q22 (right channel that doesn't work) from pin 1 to Q22 drain reads 360 ohms.

Wouldn't this confirm the signal going through the switch to the FET.

I also powered it up and took voltage measurements from Q29 the 2SA899 transistor in the same position on the Left working channel to compare.

Q29 Q30
E -29.57 E -29.80
C 0 C 0
B -28.88 B -29.23
 
Last edited:
This is really unbelievable. After fighting with this amp for years trying to get the both phono channels today was the day. I found wire J1 apparently broken along with other wires which might have broken when I pulled it apart.. I soldered all the wires back and decided to test it out. Holy **** moment both phono channels are working. I listened to part of a record and it sounded good, no hum or noise. WhooHoo put it all back together and found out my icecream turned to ****. Now the Right channel works and the left channel no longer works. It now has lost the entire left channel on all inputs. This amp is about to meet my 12 guage :mad:
 
Well, the normal/separate switch has been thoroughly deoxited with no effect. Left channel is still missing on all inputs. I don't see any broken wires, but it still can't be ruled out. Seems funny it was working fine on both phono channels before I put it back together. What could cause the whole left channel to drop? I know it is something common to all the left channel inputs, but I'm not sure what that could be. Can someone please point me in the right direction this amp is driving me nuts.
 
Try checking continuity between connector pin 24 of the pre-amp out connection and pin 1 of the amp board with the rear switch in normal position. This should at least confirm the wiring and switch between the pre and amp section.
 
DrumminDaddy said:
Try checking continuity between connector pin 24 of the pre-amp out connection and pin 1 of the amp board with the rear switch in normal position. This should at least confirm the wiring and switch between the pre and amp section.
Click to expand...

Thanks for dropping by Drummin. I connected to pin 1 on the left amp board and pin 24 the little 3 pin connector going back to the normal switch and i get nothing. Connecting to pin 2 amp board and pin 26 i get continuity. I do have a scope and audio generator that I am learning to use. What I have found is I have signal to the volume pot on J10 and J11 (loudness switch). I don't get a signal on J11-J15. I also have a signal at J7 and J8 coming out of the monitor.
 
Last edited:
If you’ve got signal at 7,8 your getting thru the volume control. Do you have signal at 24,26 on the pre-amp out connection?

I’d be wanting to find out why you don’t have connection from 24 to 1. That’s suspect. Check 24 to the normal/separate switch. Then from the switch to pin 1 on amp board.
 
DrumminDaddy said:
If you’ve got signal at 7,8 your getting thru the volume control. Do you have signal at 24,26 on the pre-amp out connection?

I’d be wanting to find out why you don’t have connection from 24 to 1. That’s suspect. Check 24 to the normal/separate switch. Then from the switch to pin 1 on amp board.
Click to expand...

Hey Drummin. Well here is where I'm at. I kept noticing the signal was dropped at the volume control on pins J13-J15. So, I pulled the volume pot and low and behold the wire J13 for left channel was broken at the connecting point on the preamp/phono board. The problem now is that wire is so short and brittle I added new wire to J13 and J15 for length. I soldered the three wires to the back of the board because I couldn't connect them back to the front of the board without disassembling the amp again. So, I cheated. Now, the Left channel is back on all inputs and plays nice and clean. Recall, I started this thread in the hopes of getting the Right phono channel to play. Well, the phono does now play on both channels. Left phono sounds nice, but the Right channel has some distortion and makes a periodic pop. The pop shows up on the meter. So, I got the Left channel back that was lost from the repair effort. I got the Right phono channel back but distorted. Distortion and pops...transistor??? Looks like I'll be tearing it apart again. Seems like everytime I try and repair something on this amp, a wire gets broken somewhere on reassembly. Thanks for your help on this. More to come :)
 
Well, at least you’re moving forward. Yeah, that solid core wire will only tolerate so much flexing before it work hardens and cracks.
I really wasn’t much help, but you’re welcome nonetheless.
 
DrumminDaddy said:
Well, at least you’re moving forward. Yeah, that solid core wire will only tolerate so much flexing before it work hardens and cracks.
I really wasn’t much help, but you’re welcome nonetheless.
Click to expand...

Yeah, one step forward and one step back. But at least I have both phono channels for the first time. Now to find and fix the distortion in the Right channel :yikes:
 
So I took a day off from the Kenwood. As stated earlier in the thread, the Right Phono channel is back but has distortion. I cleaned the selector switch again with electronic parts cleaner followed by Deoxit D5. The noise is still there. All other inputs work fine. What I know is the Left Phono sounds great, but the Right has an issue. I connected the TT and used headphones. With the tonearm resting on the record without spinning the platter the distortion shows up when I slowly turn the volume pot. It is visible on the view meters, too. I'm pretty certain the selector switch is very clean. I recall in an earler repair thread I replaced the two 2SC1345 transistors with KSC1845 transistors in the hope it would fix the missing right phono channel. I took voltage measurements on the transistors in both channels and they looked fine, to me anyway. The distortion sounds like crumpling paper to leaves rustling, then as volume is increased a little it can make a pop sound and view meter shows the bounce. I am still thinking small transistors, and hopefully not the FETs. Do these symptoms point to a transistor or ... Anybody.

Edit: So i hooked it up and it seems like fiddling with the Hi Low filters have an effect on it. The channel clears up and sounds nice, then starts to distort. Pushing the two filter switches can sometimes clear it up temporariliy and sometimes the whole channel drops off. Are these two filter switches just used by the phono input. May be I'm fighting with the Kenwood Service Bulletin on dropping channels. The filter switches only effect the phono, aux and tuner work fine.
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom