iamthejeff
Active Member
It sure seems that way. I wish I was better at reading schematics. At this point I think I am going to have to remove every diode and transistor to test for faults.
Kenwood KR-2400 fuse blows at power on
- Thread starter iamthejeff
- Start date
petehall347
the brandy coffee man
you just need to find the bad connection somewhere between the power board pin 1 and the output collectors . q19 q20 .
i am guessing its a wire between the boards then a copper trace to both outputs
power off the amp .unplug it from the wall ...set meter on ohms and measure between collectors q19 q20 and pin 8 . should read 0 ohms or very close .
same with the wire . both collectors should also be connected together . i guess they are from the voltages you gave .
i am guessing its a wire between the boards then a copper trace to both outputs
power off the amp .unplug it from the wall ...set meter on ohms and measure between collectors q19 q20 and pin 8 . should read 0 ohms or very close .
same with the wire . both collectors should also be connected together . i guess they are from the voltages you gave .
iamthejeff
Active Member
Both Q19 and 20 give 0.2 ohms between the collectors and pin 8. Not sure what you mean by the wire.
I have to go for a few hours, and I suspect it's fairly late there again. We'll have to pick this up later. Much appreciated for your help.
I have to go for a few hours, and I suspect it's fairly late there again. We'll have to pick this up later. Much appreciated for your help.
petehall347
the brandy coffee man
check between pin 8 amp board and pin 1 of the power board then ..
your reading of 1.5v suggests a bad connection along the way ..
it might only be bad under load though ...
yes its getting late here ...
just been looking at some pics of the 2400 and i see there are plugs on the boards .maybe the bad connection is there ?
also realised i had one a while back but sold it on .shame really as i could have referred to it with you .not that its needed but might have made it easier .
your reading of 1.5v suggests a bad connection along the way ..
it might only be bad under load though ...
yes its getting late here ...
just been looking at some pics of the 2400 and i see there are plugs on the boards .maybe the bad connection is there ?
also realised i had one a while back but sold it on .shame really as i could have referred to it with you .not that its needed but might have made it easier .
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iamthejeff
Active Member
0.2 ohm across those two pins also.
petehall347
the brandy coffee man
ok next is power on checks ..
we are looking for voltage drops to find the bad connection .a bad connection will show as volts .
try volts between pin 1 power board and collectors ... then between collectors and pin 8 .
a high voltage reading suggests the break is between those 2 points . this should narrow it down .
we are looking for voltage drops to find the bad connection .a bad connection will show as volts .
try volts between pin 1 power board and collectors ... then between collectors and pin 8 .
a high voltage reading suggests the break is between those 2 points . this should narrow it down .
iamthejeff
Active Member
Okay
Power board pin 1 to collectors, Q19 & 20 = 0V, Q20 & 21 = 47V
Amp pin 8 to collectors, same readings.
Power board pin 1 to collectors, Q19 & 20 = 0V, Q20 & 21 = 47V
Amp pin 8 to collectors, same readings.
petehall347
the brandy coffee man
check collectors again reference ground ..
iamthejeff
Active Member
Same as before. 1.5 V on Q19 & 20, and -47 V on Q21 & 22 measuring from the collectors.
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petehall347
the brandy coffee man
this isnt being logical to me ..
lets summarise
24v at pin 1 power board .
1.5v at pin 8 amp board .
no voltage drop between pin 1 power board and output collectors .
-24v at power supply pin 3
-47v at the other output collectors
which transistors did you change and with what ?
any chance of pictures of the boards ?
lets summarise
24v at pin 1 power board .
1.5v at pin 8 amp board .
no voltage drop between pin 1 power board and output collectors .
-24v at power supply pin 3
-47v at the other output collectors
which transistors did you change and with what ?
any chance of pictures of the boards ?
iamthejeff
Active Member
Hey, I got great news.
Since I am new to electronics I've been measuring the voltages incorrectly this whole time. I was using the chassis ground instead of the ground pin on the power supply board. Embarrassing rookie mistake.
After using the proper ground pin to measure voltages, I noticed I was getting 24V all over the amp board, on all 4 collectors of the outputs, just about everywhere. By coincidence I unhooked the speakers, measured again, and the voltages seemed to be normal (as in the service manual)
Curious I plugged the speakers back in, and sure enough, broken again. So I unplugged the speakers and tried headphones. Headphones worked! But there was still an awful clicking sound maybe 2-3 hz in frequency.
So I checked for shorts around the speaker terminals, but everything looked okay. I managed to get access to the speaker select switch and sprayed it with a heavy dose of deoxit.
And there you go, that was the problem. The speaker select switch must have been causing some kind of short which gave me all kinds of weird voltage readings in the amp board.
Now I get sound out of both speakers with no clicking. I am going to continue to take some measurements and make sure everything is working properly.
Thanks again for your patience with me!
Since I am new to electronics I've been measuring the voltages incorrectly this whole time. I was using the chassis ground instead of the ground pin on the power supply board. Embarrassing rookie mistake.
After using the proper ground pin to measure voltages, I noticed I was getting 24V all over the amp board, on all 4 collectors of the outputs, just about everywhere. By coincidence I unhooked the speakers, measured again, and the voltages seemed to be normal (as in the service manual)
Curious I plugged the speakers back in, and sure enough, broken again. So I unplugged the speakers and tried headphones. Headphones worked! But there was still an awful clicking sound maybe 2-3 hz in frequency.
So I checked for shorts around the speaker terminals, but everything looked okay. I managed to get access to the speaker select switch and sprayed it with a heavy dose of deoxit.
And there you go, that was the problem. The speaker select switch must have been causing some kind of short which gave me all kinds of weird voltage readings in the amp board.
Now I get sound out of both speakers with no clicking. I am going to continue to take some measurements and make sure everything is working properly.
Thanks again for your patience with me!
petehall347
the brandy coffee man
ah its making some sense here now ...
sorry i am to blame i should have looked more closely at the schematic .i had assumed the chassis was ground but it isn't .well it is but not the ground for the + - 20v supply .
this amp has a different grounding scheme than the majority of amps .
sorry i am to blame i should have looked more closely at the schematic .i had assumed the chassis was ground but it isn't .well it is but not the ground for the + - 20v supply .
this amp has a different grounding scheme than the majority of amps .
iamthejeff
Active Member
Looks like I spoke too soon. Not sure what happened earlier when I got it working, but now it's back to the same old problem. It's definitely related to the speaker select switch, or there abouts. There's a short somewhere.
I cleaned all the pots and switches with deoxit and I still have the problem.
I cleaned all the pots and switches with deoxit and I still have the problem.
IIRC the speaker connections are in series - if you have it on A+B you will get no sound if there aren't speakers on both sets of connections. Also, means on one side (need to follow schematic) the "-" terminal is switched and can lead to funny trouble shooting problems. Good luck.
iamthejeff
Active Member
There's something funny going on with grounding, I think.
I can use headphones fine, but that ticking sound comes back as soon as I ground the headphone jack to the chassis. I am not sure where to troubleshoot further.
I can use headphones fine, but that ticking sound comes back as soon as I ground the headphone jack to the chassis. I am not sure where to troubleshoot further.
petehall347
the brandy coffee man
i a not sure if it does ground to the chassis ... where does it look like it should be grounded ?
iamthejeff
Active Member
There's a nut that screws the headphone jack into the chassis.
Anyway I may have found something strange. Pin 5 and 7 on the power board should read +14V and -14V and they do. But when I plug in the wires that go to the pre-amp, they change to +7V and -24V
Anyway I may have found something strange. Pin 5 and 7 on the power board should read +14V and -14V and they do. But when I plug in the wires that go to the pre-amp, they change to +7V and -24V
petehall347
the brandy coffee man
is fm muting on ? if not try it on .
iamthejeff
Active Member
Same thing whether it's on or not
petehall347
the brandy coffee man
try using pin 6 of the power board as ground
