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Repairing a Kenwood C1

S

simpsonsons

New Member
Hey guys

I recently was given an old Kenwood C1. It worked great for about 30 seconds and then crapped out completely. No lights turn on and no signal is being passed.

I have it hooked to an Onkyo m5010 power amp. I may have screwed up by connecting the Onkyo to the "switched" outlet on the back of the Kenwood. This was a big mistake by me, I should have read the manual first online of the Kenwood.

My question is- do you think that is what fried my Kenwood? And if so, are there any recommendations to check first assuming this fried it?

My only major guess is that the Kenwood was in storage a long time and being vintage perhaps one or more of the capacitors are no good.

Thank you
 
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Is there a way for you to check the fuses in the unit? It may have opened the main one.
 
Hey

Thanks for the reply! I opened it up to check for fuses but I couldnt find any. I also checked the manual and didn't see any mention of them. Do you have any idea where to check for them? I feel like a true moron... usually I dont have this much trouble with electronics.
 
I just downloaded the schematic and checked it. I couldn't find a fuse either. Very strange . . . don't know how it could pass the various safety regulatory agencies. Sorry for sending you down the wrong path.

The power supply is pretty straight forward -- not to hard to test if you have a multimeter.
 
Thanks. Yeah thats a good point, Ill try to start with the power supply. I do have a multimeter.

Yeah I thought it was strange that it seems to have no fuse. Im glad Im not the only one who found it odd.
 
For future reference . Don't use the utility power receptacles for any power amplifier. Switched is 100W max ,Unswitched is 200w ..... Might be able to get by with the unswitched with that onkyo @ 160watt.
 
The switched outlet provides mains AC, located before the transformer/regulated supply etc...
Possibly burnt out the power switch. With amp unplugged from mains, set the amp power switch to ON
then measure the resistance from the UNSWITCHED outlet left side to either SWITCHED outlet left side.
Repeat for unswitched right pin to switched right pin, expect near short in both cases.
 
Thanks for the help!

I was wondering about the power switch as well, I read that overloading the switched outlet can fry it.

I checked the power switch for continuity and it seems to be working OK.

The reading for the pins as suggested was .2 killo-ohms on all pins.


I did a closer examination of the board and caught what might be blown capacitors and some corroded jumpers. c6, c5, c44, c43 in particular. I thought it was a glue when I first looked last night but they seem to be blown to me now...


I included some pictures below. What do you think, should I start with replacing those caps and see if it fires back up?





https://www.dropbox.com/sh/x18q8bmr1ohrfh8/AABOqgqJcloTH62SAQ6fFoj3a?dl=0
 
That just looks like the glue they put on in assembly to hold the caps in place until the board is wave soldered.

I would just start tracing power from the power cord input forward through the power supply until you find where you are losing power.
 
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simpsonsons said:
I did a closer examination of the board and caught what might be blown capacitors and some corroded jumpers.
Click to expand...
Appears to be just component glue, scrape off if it's brittle. Corroded jumpers should be replaced.
Probably need basic health check of power supply.
 
Check dc voltages at wire wrap pins 12-16 on tone board. Black meter probe connected to chassis.

upload_2019-10-2_5-40-19.png
 
Got zero voltage at the pins 12-16


Also got zero voltage at the pins 18, 17, 10



Voltages on the switch pins when turned on were 18v at both the red and white wire


Likewise got voltages back at the outlet terminals. Didnt write them all down but they all seemed reasonable.

Seems like the electric is... not making it past the transformer? That would be a big bummer if the transformer is fried as I suspect its the most expensive part.


I will try the jumper on the switch tomorrow. But it is getting continuity and voltage when switched on. It gets zero continuity when switched off. The switched outlets are registering voltages when turned on. These all make me think the switch is working OK? I would love it to just be a fried switch though but evidence doesnt seem to be pointing that way to me.


I have added some pictures of the transformer to this dropbox folder in the unlikely hope they have a visual clue about if they are blown or not.

https://www.dropbox.com/sh/x18q8bmr1ohrfh8/AABOqgqJcloTH62SAQ6fFoj3a?dl=0


Thanks for all the help people have given!
 
The unswitched outlet provides mains AC voltage when the amp is plugged in and wall socket
switch is on. The switched outlet also provides mains AC but when the amp power switch is on.
The voltages you measured should be AC mains.

DC voltages are expected at pins 12-16.

AC voltages are expected at pins 10,11,17,18

I will assume you had your meter correctly set for each.

Your measurements point to transformer failure, difficult to see how this would occur
by overloading the outlets...

With amp switched off and unplugged from wall, measure the resistance between the two
pins (L&R) of a switched outlet. This is the same as checking the primary winding for continuity.
Expect less than 100 ohms, the reading may ramp/climb due to charging of C1.

Repeat resistance measurement on secondary between pins 10 & 11, again C41 will charge up.
Repeat for pins 17 & 18, note C42.

The capacitors cause some complication, expect the resistance to climb from a small (10?)number.
Don't expect near immediate 2-10kohms
 
Looks like

Resistance between L and R is about .3 ohms

Between points 10-11 is 5.7 ohms

Between points 18-17 is 2.7 ohms


Double checked my meter and its digital so it automatically determines ac or dc voltages and all the pins are at zero volta

Jumped the electrical switch and didnt work


Also i must apologize I misread my meter above and the reading doe the pins between Unswitched and switched left pins are .2 ohMs, not kilo-ohms.





mbz said:
The unswitched outlet provides mains AC voltage when the amp is plugged in and wall socket
switch is on. The switched outlet also provides mains AC but when the amp power switch is on.
The voltages you measured should be AC mains.

DC voltages are expected at pins 12-16.

AC voltages are expected at pins 10,11,17,18

I will assume you had your meter correctly set for each.

Your measurements point to transformer failure, difficult to see how this would occur
by overloading the outlets...

With amp switched off and unplugged from wall, measure the resistance between the two
pins (L&R) of a switched outlet. This is the same as checking the primary winding for continuity.
Expect less than 100 ohms, the reading may ramp/climb due to charging of C1.

Repeat resistance measurement on secondary between pins 10 & 11, again C41 will charge up.
Repeat for pins 17 & 18, note C42.

The capacitors cause some complication, expect the resistance to climb from a small (10?)number.
Don't expect near immediate 2-10kohms
Click to expand...
 
simpsonsons said:
Resistance between L and R is about .3 ohms

Between points 10-11 is 5.7 ohms

Between points 18-17 is 2.7 ohms
Click to expand...
0.3ohms primary winding resistance is low. The primary winding has more turns than either secondary
so would expect at least 5.7ohms (probably a different AWG but still >0.3ohms). Possibly C1 has failed, try
replacement (0.1uf, across the line type X), they are designed to fail short, the other alternative is a primary short.
 
Thanks! Hopefully that is it. Looks like a straightforward thing to replace.

Confused about .1uf. The service manual states ceramic 100pf with +- 5% tolerance which would mean .0001 uf right? I don't doubt you have the correct reading though Im just trying to learn why Im getting it wrong.

Even more confusingly the reading on the cap itself says:


MY
103P
(m3 74



Wouldn't that mean 10000 pf ? (10*10^3) = .01uf

and 74volts


I apologize for my ignorance just trying to learn how to rad a small cap like that properly.

I included a picture on the dropbox if interested.

https://www.dropbox.com/sh/x18q8bmr1ohrfh8/AABOqgqJcloTH62SAQ6fFoj3a?dl=0



Also having trouble sourcing a capacitor?

Assuming 0.1 uf is correct, I found one on Mouser but with 1kDCV. Dont I need something closer to 75-100 VAC? Also tolerance is much worse than 5%

https://www.mouser.com/ProductDetai...=sGAEpiMZZMt1mVBmZSXTPCZtCCc5J7ioIEmFsI8iS3U=
 
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