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Kenwood KA-7100 re-cap with pictures.

leesonic

leesonic

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Here are some pictures of my Kenwood KA-7100 re-cap. I used all Nichicon KW audio grade caps throughout, except for where there were orange Elna caps, in which case I used Nichicon KL low-leakage.

Some observations made...

1) If you have trouble setting the offset, try cutting the yellow and blue input wires to the power amp. This separates the pre and power amps, and will show if you have a bad component in the pre-amp causing a DC offset. This might be old news for experienced techs here, but I'm mentioning it to help others.

2) Don't bother replacing the single bi-polar electrolytic with a fancy Nichicon Muse. It is part of the protection circuitry, and isn't really in the signal path. Just a plain old VP series will suffice.

3) Unless you want the absolute best sound while using the subsonic filter, don't bother to change the two tantalum bead capacitors between the toggle switches.

Lee.
 
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Main board - power supply and power amp

Power supply before

KenwoodKA-7100-01.jpg

KenwoodKA-7100-02.jpg

Power supply after

KenwoodKA-7100-05.jpg

KenwoodKA-7100-06.jpg
 
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Looks good! How hard did you find re-caping the KA-7100? I have one myself that could probably benefit from a recap. I have thought about giving it a try this summer.
 
bored184 said:
Looks good! How hard did you find re-caping the KA-7100? I have one myself that could probably benefit from a recap. I have thought about giving it a try this summer.
Click to expand...

It's a very easy amp to work on. The main board is easily accessible from underneath with the bottom panel removed. The control and pre-amp boards are somewhat harder, since you have to loosen the front and rear panels. But the service manual shows you how to do this, not that it's not easy enough to figure out.

The one beauty of it though is the components are inserted through the board, and don't have the wires bent over. This means you can de-solder them, and they will almost drop right out. With my Pioneer SA-9800 the component leads are bent over onto the board, meaning you have to de-solder and then pull them out.

Lee.
 
Control and pre-amp boards

Control board before

KenwoodKA-7100-09.jpg

KenwoodKA-7100-10.jpg

Control board after.

KenwoodKA-7100-11.jpg

KenwoodKA-7100-12.jpg

Pre-amp board before

KenwoodKA-7100-14.jpg

Pre-amp board after

KenwoodKA-7100-15.jpg

KenwoodKA-7100-16.jpg

Lee.
 
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I've got a KA 7100 and have done the relay circuit, caps, set the DC offset and Bias and the amp is running great. All voltages are in range.
I just have one issue with the control board with Tone ON I'm getting a faint white noise hiss, a bit like tape hiss. I'm getting good treble and bass response and loudness settings work as expected. I've replaced transistors Q7, Q8, Q9, Q10 and Q3, Q4, Q5, Q6. I've used KSA992FTA for the PNP and KSC1845FTA for the NPN's with no change in the hiss.
With Tone defeated the hiss is not there. The amp still sounds good, very well balanced, but I'd prefer to have it just as quiet with Tone ON.

Any thoughts? This is my first 7100 so wondering if any of you guys have a similar experience?
 
I've never noticed the Tone Defeat switch (tone jump on the schematic). I've only had it set to defeat. Clean the switch again? And the tone pots. And the high filter switch. if it is both channels, it is usually a power supply issue but i don't think I've touched the switch once I cleaned it. I might have replace Ci23,24 with a WIMA MKS2 but can't find a pic to verify.

there are a few electrolytics in the signal path (Ci17, Ci19, Ci21, Ci23). you might need to put a scope on the treble side to narrow down the problem.
 
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