Kr-7060 occasional pop/crackle

Gertjan90

Member
Hi guys,

A while ago, I posted about my new Kr-7060 that I'm planning to clean up.
But while waiting for the replacement meters and bulbs (thanks Gort!) I encountered a hopefully small problem.

When I've been listening to music for a while (+-1 hour), sometimes a crackle or pop will occur.
As best I can tell, this happens both in the two channels and in one at a time.
This occurs both in AM/FM and aux fuction.
There are no pops when powering on or when turning the controls/selectors. I've spotted no obvious bad connections/solders with my untrained eye so far.

I cleaned up the switches and pots, except for the function and tape source ones, as they are on the very back of the receiver and very hard to get at.

Are there any other possible causes of this problem?

The tape switch is my main suspect at the moment, any tips on how to get to it?

By the way, this receiver puts out a faint hiss when powered on, regardless of input or volume level.
It's only audible with high sensitivity speakers, should I be worried?

Any help is appreciated.
 
Service manual shows outhouse 2SC458 being used, but couldn't find it. Also 2SC1345 Qk3,4 in the power supply.
Suggest replace Qk3,4 with KSC1845 since both channels affected. Both 2SC458 and 2SC1345 have a strong
history of going noisy.

The hiss may be aged caps/leakage. Recap, replacing those low noise/leakage types with Nichicon KL, some use MKS, your choice.
Check dc offset, make sure it's not causing the problem. Check bias as part of general house keeping.
 
I had one that had a pretty loud hiss. Replacing Qi1 and Qi2 (2sc1345) on the control (tone) board with KSC1845FTA. solved the problem. Could be the source of the popping as well if you're lucky.

On the power supply a board, Qk2 and Qk3 are the DC detect (neg and pos) for the protection circuit and Qk4 is the relay driver. Per the recommendation of EchoWars I replace Qk3,4 (2sc1345) with KSC2690AYS and Qk2 (2sa733) with KSA1220AYS. I doubt these are the source of your problem, but as long you have it torn apart....

Getting to the tape and selector switches is no fun.

- Remove bottom and top covers plus both outer plastic side panels. Also on the bottom, remove the 4 screws that attach the plastic rear panel to the chassis

- Remove the "adapter" jumpers from the rear panel RCAs

- Up top, you'll see an orange and a white antenna wire on the tuner board - detach these from the cardboard-ish L shaped bracket at the front of that board.

- Put the receiver on the bench with the back panel facing you, and hanging over the edge, but not so far it will fall off and smash your toes. Remove the circled screws - 2 per side

P3140037_zps015e67f4.jpg

- slide the rear panel toward you wiggling a bit side to side, then it will hinge down as shown. Don't force it - often the antenna cable will hang up on the top left corner of the pre-amp board. Just move it out of the way.

P3280132_zps87385c61.jpg

- Unscrew the AM antenna from the rear panel (1 screw, plastic clamp) and lay the antenna on the chassis by the filter caps

- remove the 6 screws that fasten the pre-amp board to the rear panel. Gently maneuver it so comes free from the rear panel and you can see the two switches, which have yellow tape on them

-spray your cleaner down through the switches and work them a bunch of times. In the photo I was using the regular front panel knobs - the sound injection knob is a better choice. Turning the splined shafts with your fingers will peel the skin off

P3280133_zpsb18ae87b.jpg
 
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On the power supply a board, Qk2 and Qk3 are the DC detect (neg and pos) for the protection circuit and Qk4 is the relay driver.
Yeah, got that wrong. Got a bit excited to see the 2SC1345 and didn't look into it ...
 
Wow thanks for the input guys!
Especially the pics, Gort.

If I were to replace the transistors Qi1, Qi2 and Qk2,3 and 4, would I need to do some adjusting on the bias?
Because that kinda scares me a bit..
But I'm definitely going to give it a try.

Tommorrow, I can go pick up my replacement meters and bulbs from the post office, so I can have a little fun over the long weekend.
I'll clean the pots in the back following the instructions and I'll start making a list of the transistors and caps I'll eventually be replacing.

I guess I'll be turning this one into more of a longer term project.

By the way Gort, you would happen to have any pics of, or tips for accessing the meters?

Thanks in advance.
 
Bias shouldn't be affected, but it should be checked and adjusted anyway - it's not difficult. Post back if you need help.

To access meters -

Remove top & bottom covers and plastic outer side panels.

Remove all knobs - they all come off by pulling on them except the tuner knob. You'll need a 1.5mm hex key for that.

Remove the 3 toggle switch caps - pull.

Remove the two beveled flush mount phillips head screws on the top edge of the face plate.

Behind the speaker and selector knobs there is an 11mm nut/washer - remove those, then remove the faceplate.

Remove the dial glass (which is plastic) by removing the 3 beveled phillips screws.

Remove the 3 round-top phillips screws that attach the meter panel, The meter panel should now come free of the chassis - you have to wiggle it around a bit. Kenwood wasn't exactly generous in the extra wire department, so it won't come out too far, but far enough Make a note or photo of the wiring colors, then clip the wires close to the meter terminals.

The meters attach to the panel with some sort of adhesive. Just get your finger nails under an edge of the meter and pry them off taking care not to bend the panel. Takes a little grunt, but not too bad.

Attach the replacement meters to the panel with high quality double sided tape. You'll see where to put it.

Strip a small amt of insulation from the wires, put them through the lead holes - paying attention to which wire goes where - .bend them over and solder them in.

Since one of your meters was missing, here's a picture of the wire colors. Kenwood wasn't terribly consistent in wire colors - hopefully yours has the same colors as this one - if not, post back and we'll figure it out.

P1011145.JPG
 
So, time for a small update:
I've installed the meters and everything works fine!
But.. the meter light wont work, I've tried different lights but no go.
The strange thing is that I don't get any voltage over the pins that should power the meter light.

Any ideas?
 
Those run on AC, not DC. Set your meter to AC and see what you get. Do the dial lamps work?
 
right, that was silly of me.
I get about 7.5 VAC.
I'll go try another bulb first.
All dial and indicator lights work.
 
Okay, I took these at the work bench just now, I'll try to take better ones after dark and with the case together.

hmm. that didn't work.
Here's the link for the album:
http://imgur.com/a/nZS04
x4fQIR3

yhxohnd

kmHYRnr
 
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