The Overseas Only Kenwood Model KR 790

[Mark R]

Ok, I took some shots of the Ebay switch which is the same as the one in the unit. Except the shaft is different. Butt he shafts are interchangeable. Also some shots of the Reverb Board. I'm going to swap out hose two diodes now. Just another shot in the dark. They did test good in circuit on diode check with my Fluke 8808A 6 digit DVM.

Here's the pic's

[CapLeaker]

On the second last picture, look at C28. Is that cap installed backwards?

[Mark R]

On the second last picture, look at C28. Is that cap installed backwards?

Yep..sharp eye's Leaker. I'm aloud one backwards cap out of the 20 I replaced L.O.L. on that board. Anyway It checked good even being in backwards. But I installed a new one and checked it with the LC103. Fired up the unit and still ...Audio in the off position ...Next click Mic only... that works...but no reverb...Light comes on ( That's what Board #13 & 14 run from the switch) ...Then next click is supposed to be Audio and reverb and Mix. I get the reverb light but totally nothing else. That cap that was in backwards is in the delay line control feed.

I'm still leaning towards that switch or a defect ( Cold Joint ...Broken trace) or something ???

Anyway tim for Lunch. Gives you time and me also to ponder WTF!!! L.O.L.

Regards: Mark

[CapLeaker]

I am saying it’s time to bring out the oscilloscope and see where the audio disappears. Whatever the problem is affects both sides. Switch, muting, an IC etc.

[Mark R]

I am saying it’s time to bring out the oscilloscope and see where the audio disappears. Whatever the problem is affects both sides. Switch, muting, an IC etc.

Tried that once but that switch has to be traced out. I'll hook up the scope and start probing again. Also check voltages in and around the circuit which I have done before. I have another BBD in route. it'll be about a week. Like you say...Sometimes the new stuff you get is garbage. if it passes audio and Mic but no reverb it won't hurt to throw another one in.

Also, I have another KR 790 that the Reverb circuit which does work ok. But that one has a dead Power L.E.D. display. That one should be an easy fix. I could put the other one up next to the bad one and compare scope traces. Maybe I'll have to go that route if I can't trace what and where on the bad one.

What you suggest is right... Use the scope.

Thanks:
Mark R

[petehall347]

fix the regulated voltages and all will be well .

[Mark R]

fix the regulated voltages and all will be well .

Thanks Pete,

Got the correct voltages coming in at the board @ +24 Volts DC and - 24 Volts DC. Need to Check around to make sure they are what the schematic calls for at the IC pins and other parts of the circuit. But this all changes when you turn that multi contact switch.

That's why this think is a PITA as there is no Theory of operation or service manual to follow signal flow at the different switch positions. As Capleaker says it's time to break out the scope for the umteeth time.

[Mark R]

Thanks Pete,

Got the correct voltages coming in at the board @ +24 Volts DC and - 24 Volts DC. Need to Check around to make sure they are what the schematic calls for at the IC pins and other parts of the circuit. But this all changes when you turn that multi contact switch.

That's why this think is a PITA as there is no Theory of operation or service manual to follow signal flow at the different switch positions. As Capleaker says it's time to break out the scope for the umteeth time.

Hey Capleaker:

Just dropping by to let you know ..I had a slight detour . Lost my rear brakes on my Classic Ride. Been rushing around to get parts to do the repair. Will be back on the Kenwood soon,.

I'll keep you posted.

Regards: Mark R