KR-9050 problems and repair

xwarp

xwarp

Active Member
KR-9050 problems and repair FIXT!

I posted a few days ago about the KR-9050 that I picked up at goodwill for cheap.

I did not have a chance to test it until yesterday, and, unfortunately, it has issues..... :thumbsdn:

Looks like I'll be busy this weekend trying to figure out what is taking out the 16vac going to the tuner board.

Will post results as I find them.

As it stands:

1. No lights, at all. Not even the indicators for the function.
2. No sound from AM or FM selection.
3. That hum you might normally hear from Phono1 and 2 is there.
4. Lots of deoxit will be needed for the pots and switches.
5. I can input through the mic input and the amp section sounds fine.
6. All voltages except for the 16 vac that feeds the lamps, and other circuitry on the tuner board is being shorted out.
7. Aux input works just fine.
 
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Drooled over your first posting and your $9.95 purchase price. The value of that thing really gives you a fairly decent repair budget before you would approach "going overboard". Really a beautiful Kenny. I hope you get it back to its glory. Good luck with it.
 
I don't have much planned for the weekend since the wife will be gone for the weekend, so I'll be digging into it more.

A poster sized print out of the schematic would be nice though.
 
I've got the service manual already and what I meant when I stated a "poster size" print was actually being able to print one out that large instead of in sections.

I think it's a lot deeper than just that regulator since none of the lamps, in that circuit, operate.

Also should note that there is no am/fm operation. (oh...noted in 1st post)
 
The schematic in the service manual from hifiengine is fine, the problem is that I can't print the schematic out on anything larger than 11x17 because I don't have access to anything that prints larger than that without doing it in sections.

Does that clear up what I am talking about?

But thanks for the help though!
 
xwarp said:
The schematic in the service manual from hifiengine is fine, the problem is that I can't print the schematic out on anything larger than 11x17 because I don't have access to anything that prints larger than that without doing it in sections.

Does that clear up what I am talking about?

But thanks for the help though!
Click to expand...

What you do is print it in sections and tape them together to make a large print.
Get that light bulb out of the fuse holder until you find out where the short is. You could blow the transformer winding. Use an ohm meter to find the short. If it isn't on the input side of the regulator, look on the output side. Then start disconnecting things until you find the short.
 
Will have to hit up a FedEx office locally for that large print.

Found shorted diode, buried under that damn glue that they use to hold the caps in place for the wave baths.

Got that replaced and the lights are now working.

No AM or FM tuner operation. Dead silence. It doesn't appear that the tuner circuitry is being turned on at all since there is no deflection in the tuning meter.

Looks like I am missing VSS for most of the logic on the tuner board.
 
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Got her fixed and running.

Now it's on to cleaning and replacing bulbs.

The problem?

Hardly ever do I see an issue where symptoms would clearly point to a short to to near ground, and it not be a short.

Turns out it was an OPEN transistor.

This transistor was part of the circuitry that enables the 12 vdc to the tuner logic. This transistor was also fed by the half wave rectified voltage that provided the same 16vac to the lamps.

Having replaced the shorted diode, and still not having the "turn on" of the 12vdc logic voltage because of the open transistor, explains why the 8 watt bulb in place of the 2a fuse worked since it was only drawing 38mA.

In any case, all looks to be good to move forward on this powerhouse!
 
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Nice fix! You've got one nice receiver now. Probably one of the best (if not THE best) receiver that Kenwood ever built. It's a rare one as well- hope you enjoy it. I'm jealous!

Please post some pictures when she's show-worthy so I can drool!
 
turnitup said:
Nice fix! You've got one nice receiver now. Probably one of the best (if not THE best) receiver that Kenwood ever built. It's a rare one as well- hope you enjoy it. I'm jealous!

Please post some pictures when she's show-worthy so I can drool!
Click to expand...

Right at the moment, trying to decide if I want to stick with the incandescent bayonets or go l.e.d. on the dial lamps.

And to be honest, I'm not sure what I'm going to do with it when I'm done.

It's certainly a nice looking and sounding receiver, but I prefer the backlit dials. (i.e. Marantz)
 
Nice job troubleshooting those issues.

FWIW, while everyone seems to be getting on board with LEDs, and from a heat and longevity perspective they do make sense, I prefer the look of incandescents in receivers. To me they are warmer and less clinical.
 
I just upgraded a Marantz 2330b to LEDs and really like the change. I went with a "white" option, it really brought the color back to the receiver. The old bulbs were casting a yellow hue and every time I went in to change them more of the delicate plastic surroundings would tend to chip away/break - I assume that the heat from the incandescent bulbs contributed to the plastic degradation. I like the result and the fact that (hopefully) I won't need to be servicing the bulbs any time soon. Haven't upgraded any of my Kenwoods yet because the standard bulb conversions aren't quite as easy to upgrade as the fuse-type bulbs for the Marantz units.
 
Yeah, I did my Marantz 2245 and 5020 tape deck about 5 years ago with L.E.D.

The look is much more harsh in blue than the original softer turquoise look with the incandescent.

My avatar is one of the meters from the tape deck with the l.e.d.s.
 
If you aren't a fan of your 9050, you could probably sell it for about the same price as a 2325 (one of my Marantz favorites). Your New Kenny has some significant value to it!
 
Would not mind keeping it, but I'm eyeballing a HP 100hz-1.5ghz spec/an locally that I've been wanting for a while now.

My weak spot is test equipment!
 
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