KA-7100 No sound

sajjad amer

Active Member
I have recapped the amplifier and now there is no sound. Amp powers on, I hear and see the relay click but there is no sound.

On aux input if I turn the volume to max, I can hear very faint sound coming from 4 Toshiba transistors, it is the same sound as the music I am trying to play.

During the "restoration" process (read destruction as it was working before), I broke the speaker selector switch. I bought it from Israel, like for like and replaced all wires but still no sound.

Can anyone here please help me fix this amplifier. I am a novice but help from members here I have already fixed 2 amps.
Any Help would be greatly appreciated.
 
Can anyone please confirm I'm using correct selector switch and if my confections are correct?
 

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Thank you for guidance. When volume is turned to full there is very faint sound on only left channel in head phones.
Right channel has nothing but static at times when flipping switches.
I double checked mute was off, on tape selector I had source and aux selected as input.
What should I do next to diagnose this issue?
Thanks
 
I'd put a scope on pin 5 of the pre amp board (X08-1570) to check signal on the left channel or pin 4 for the right channel. If you are not getting signal, the switch needs review.

I always get nervous turning up the volume to max on an unknown amp. I hate to cause other problems.

I don't have a 7100 and just looked at the schematic I found in the AK library.
 
Ditto the above, although it hasn't been determined that you even have a scope.

The tone defeat, loudness, and mode switches are notorious for completely defeating the signal. At least toggle them a few times with volume setting at no more than 9 o'clock.
 
Download the KA-7100 schematic, get a DMM with a continuity buzzer, and follow the leads through the switch and out to the speaker connectors. Using a multi meter allows you to test without any power running..less chance to do any damage.

if you don't have a scope, get a continuity buzzer like John recommends. You can check the non phono inputs (aux,tuner,tape) with out any power.

I looked at the schematic and you can follow from the aux input (use a rca male connector) to pin 5 per above. I'm assuming you replaced SD1.

Unplug the amp, select the input to aux and beep it out between the aux and pin 5 on the pre amp board. Then you can test the tuner and tape inputs the same way.
 
Thank you so much every one for your guidance. I do have a scope but I do not know how to use it :)
I was going to put ground lead to chassis and touch the probe on the pins specified, with audio signal on aux.
But this MM method is much more convenient as I do not have a signal generator as yet for scope, I hope to find one on eBay soon.
@rickl , excuse my ignorance but what is SD1 please ?
 
Are you getting voltage to the four output transistors? Just connecting the negative of your meter to the ground, and touching the metal cases will tell you if you are getting voltage to them or not.

If you are not, check around the power supply for blown fuses.

If you are getting a voltage at the output transistors, try soldering a wire to L1 and L2, and use a TEST SPEAKER or other old speaker between this wire and ground, and see if you get any sound. This will bypass the protection relay, so if you have anything wrong with the amp, that speaker could blow. Hence the use of a test speaker.

Lee.
 
I have managed to find my mistake, speaker selector switch wiring was incorrect. I have managed to get the sound from Speaker A , Speaker B separately but I am unable to get sound from both speakers A+B at the same time.
After listening to it for 15-20 minutes at 1/4 volume, loud thud and now no sound from Left Channel. I have checked my both speakers are fortunately working but need advice where to start diagnosis now. I will enclose picture of rewired switch from my mobile shortly.
Thank you every one for your kind help appreciate it
 
OK, an old thread but maybe helpful for the next person.

Troubleshooting no left channel in KA-7100. No signal at pin 5
of preamp. Dismantled & cleaned input selector and tape monitor.
Noted zero ohms between pin 5 and GND. Removed mode switch, pin 5
nolonger short to GND.

Dismantled & cleaned mode switch. No joy.
Will look downstream at attenuator etc but have a nagging feeling it's
the input selector since it grounds un-used inputs.
IMGA0130.JPG

For people with similiar issue, suggest check resistance at pin 4 then
pin 5 to GND. Mode and loudness switches would be low likelyhood.


Amp was working fine after recap then sat idle for a year until now.
Amp has been pimped with speaker posts, apologies to the kenwood guardians but...

IMGA0131.JPG
 
So much for trying to help out the next guy.
Turned out to be a squashed resistor, R3 making contact with R5.
Left channel audio going to GND. Not sure why it was mounted so.
Very lucky it did not cause smoke.


R3_R5.JPG

Candidate for "dill of the week"
Least the switches are clean.
Attenuator wasn't too bad...

Attenuator.JPG
 
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