Kenwood KR-6600 power supply board

[dimitrije.tu]

Hello,

I bought my first vintage receiver, a Kenwood KR-6600 model. I took the cover off and there was a lot of dust in it. I cleaned it all up.

I noticed that the relay does not open when I turn on the device, so after 10-15 minutes it opens by itself.

I replaced with the appropriate components:
- electrolytes (Ck1, Ck2, Ck4-7)..........................Panasonik with low ESR
- metal film resistors Rk1, Rk3 and Rk18
- transistors Qk1 - Qk4
- Diodes Dk1 - Dk4
on board (X00-1770-10). I got the signal and now it turns on the relay.

After measuring the pins on both power boards I noticed that:
- pin 12 shows 23.4 VDC, instead of 13 VDC ''A'' (X00-1770-10)
- pin 13 shows -1.6 VDC instead of -7 VDC ''C'' (X00-1790-10)

I would like to ask you for help on how to bring the voltages to the prescribed levels ?
In attachment is Schematic diagram of units ''A'' and ''C''.

Thanky you,

 

[rickl]

i've only worked on one so i'm not an expert and it was returned to it's owner.

I'd focus on "C". Verify bridge is working. measure pins 1, 2. Don't forget a DBT (60-75w bulb).

BTW, pins 11, 12 on "C" are Vac.

 

[dimitrije.tu]

Thank you.
I already checked pins 1 and 2.
Pin 1 is 48.5 VDC
Pin 2 is - 48.8 VDC

I'll check and measure pins 11 and 12 later after work and let you know

 

[mrk229]

After measuring the pins on both power boards I noticed that:
- pin 12 shows 23.4 VDC, instead of 13 VDC ''A'' (X00-1770-10)
- pin 13 shows -1.6 VDC instead of -7 VDC ''C'' (X00-1790-10)

When you measure pin 12 make sure it is in FM mode and tuned to a stereo station and the stereo lamp is lit. If any of those conditions are not met then you will not be measuring the actual voltage. I'm guessing the voltage is OK when the dropping resistor is loaded.

As for pin 13 I need to see more of the schematic, which i don't have handy this morning. There is a whole bunch going on behind pin 13.

Thanks @rickl for the schematic snippet!

 

[dimitrije.tu]

Hi,
after measuring on "C" board the values are:
Pin 11......0.022 VDC
Pin 12......0.024 VDC
Voltages are unstable.

FM mode and tuned are ON. I noticed that the stereo lamp was NOT lit.
I checked the bulb and it's fine. The voltage coming from pin 3 of the "A" board is 23.4 VDC.
Now I assume that I have no real voltages.

 

[mrk229]

Hi,
after measuring on "C" board the values are:
Pin 11......0.022 VDC
Pin 12......0.024 VDC
Voltages are unstable.

FM mode and tuned are ON. I noticed that the stereo lamp was NOT lit.
I checked the bulb and it's fine. The voltage coming from pin 3 of the "A" board is 23.4 VDC.
Now I assume that I have no real voltages.

Pin 11 and 12 on the "C" board are the AC input to the bridge rectifier, you won't have DC there!



If the Stereo "Beacon" is not lit when tuned to a known good stereo station, you may have a problem on the MPX board. Or the mono switch is pushed in.
You say the bulb is good I assume you ohm checked it?

Find pin 25 on the tuner board. measure the DC voltage there. If not tuned to a stereo station or the mono button is pressed you should have around 20 or so volts DC.
That will tell us if the circuit from the power supply through the bulb is good.

Tune to a known stereo station (listen though headphones to be sure it is in stereo) (mono button not pressed). Pin 25 should go low (zero volts) and bulb should light.
If it does not go low then ground pin 25 and see if the lamp comes on. If the lamp lights you have an issue on the tuner board. If you get the lamp to light go back and check pin 3 on the "A" power supply it should read around 13 volts.

 

[sregor]

IMHO the power supply boards are probably OK. My guess would be a MPX problem. Commonest is the 76Khz VCO trimmer gets dirty.
Tune in strong station - make sure center tune is correct, mark location of VRg2 trimmer on tuner board, put some contact cleaner and move itack and forth, seeing if the stereo light comes on, and stations tune in stereo...There are other things can cause no stereo, but this is the commonest and easiest to check.

 

[dimitrije.tu]

Thanks mrk229
Yes, the bulb is good. I checked it in other positions AM, FM, AUX and bright. The MONO switch is not pressed.
- When the scale is out of the stereo position the voltage at pin 25 is 23.3 VDC.
- When the scale is in the stereo position, the voltage at pin 25 is 0.42 VDC but the bulb does not light.
When I turn on the mono switch, there is a difference in the sound on the bookshelf speakers I have connected. I think the stereo does the job.
The voltage on pin 3 of the "A" board is 14.7 VDC.

I didn't quite understand this:
'If it does not go low then ground pin 25 and see if the lamp comes on.
If the lamp lights you have an issue on the tuner board.

 

[dimitrije.tu]

IMHO the power supply boards are probably OK. My guess would be a MPX problem. Commonest is the 76Khz VCO trimmer gets dirty.
Tune in strong station - make sure center tune is correct, mark location of VRg2 trimmer on tuner board, put some contact cleaner and move itack and forth, seeing if the stereo light comes on, and stations tune in stereo...There are other things can cause no stereo, but this is the commonest and easiest to check.

I also tried what you wrote. I found it somewhere in the text on A.K. ...
I turned the VRg2 trimmer where I set the scale to a strong signal.
But he didn't happen to turn on the lamp. I didn't add DeoxIT, and will try again after office hours.

 

[mrk229]

Thanks mrk229
Yes, the bulb is good. I checked it in other positions AM, FM, AUX and bright. The MONO switch is not pressed.
- When the scale is out of the stereo position the voltage at pin 25 is 23.3 VDC.
- When the scale is in the stereo position, the voltage at pin 25 is 0.42 VDC but the bulb does not light.
When I turn on the mono switch, there is a difference in the sound on the bookshelf speakers I have connected. I think the stereo does the job.
The voltage on pin 3 of the "A" board is 14.7 VDC.

I didn't quite understand this:
'If it does not go low then ground pin 25 and see if the lamp comes on.
If the lamp lights you have an issue on the tuner board.

- When the scale is out of the stereo position the voltage at pin 25 is 23.3 VDC.
- When the scale is in the stereo position, the voltage at pin 25 is 0.42 VDC but the bulb does not light.

We have some contradiction going on. Unless I have misread the schematic or given wrong instructions the information you just provided concerning pin 25 indicates the stereo light should be working. What does the voltage on pin 3 of the "A" board have to do with it? Did you mean pin 13?

Pin 25 of the tuner board is either:
High (open circuit) when not tuned to a stereo station, or the mono button is pressed. Lamp cannot be lit because the circuit is not complete (open)
Low (closed circuit) when tuned to a stereo station the MPX IC connects pin 25 to ground completing the lamp circuit and lighting the bulb.

Can you follow the wire from from pin 25 of the tuner to the stereo lamp? Something is not adding up, Power comes from pin 13 on the "C" supply through the bulb filament and then on to pin 25 of the tuner board. If the bulb was open you would have no voltage on pin 25

The part you did not understand was meant to test the lamp circuit if pin 25 was not changing state, high to low. If the lamp circuit is good grounding pin 25 will force the lamp on. Since pin 25 is changing state that is of no concern now.

Yes, the bulb is good. I checked it in other positions AM, FM, AUX and bright.

Not sure what this means. Checking it in other positions? The bulb can only light when in FM mode.

 

[mrk229]

Green line is the Beacon power to the lamp ass'y board from "A" power board where it goes in on pin 1.
Power from pin 1 goes through the "beacon" bulb and comes out on pin 12.
Pin 12 on the lamp ass'y board will go to pin 25 on the tuner board. Yellow line is the path to pin 25 on the tuner board. (board not shown)

If the bulb is good and the lamp ass'y has not been messed with grounding (low) pin 12 on the lamp ass'y board or pin 25 on the tuner board should make the lamp light.

 

[dimitrije.tu]

In the previous post, information was requested about the voltage on pin 3.
''If you get the lamp to light go back and check pin 3 on the "A" power supply it should read around 13 volts.''
This is clear to me and I fully understand:
''High (open circuit) when not tuned to a stereo station, or the mono button is pressed. Lamp cannot be lit because the circuit is not complete (open)''
''Low (closed circuit) when tuned to a stereo station the MPX IC connects pin 25 to ground completing the lamp circuit and lighting the bulb.''

Yes, pin 25 is changing state that is good for now.

I tried the bulb in the AM position, of course I set the switch to AM. The bulb lights up and that means it's working.

Voltages on pin 12:
When is high (open circuit) when not tuned to a stereo station, and the MONO button is not pressed was measured 23,4 VDC.
When is low (closed circuit) when tuned to a stereo station, and the MONO button is not pressed was measured 0,4 VDC, but no light.
On the diagram, pin 12. should have a voltage of 13 VDC. Do I need to check any of the components on board "A"?

 

[mrk229]

In the previous post, information was requested about the voltage on pin 3.
''If you get the lamp to light go back and check pin 3 on the "A" power supply it should read around 13 volts.''
This is clear to me and I fully understand:
''High (open circuit) when not tuned to a stereo station, or the mono button is pressed. Lamp cannot be lit because the circuit is not complete (open)''
''Low (closed circuit) when tuned to a stereo station the MPX IC connects pin 25 to ground completing the lamp circuit and lighting the bulb.''

Yes, pin 25 is changing state that is good for now.

I tried the bulb in the AM position, of course I set the switch to AM. The bulb lights up and that means it's working.

Voltages on pin 12:
When is high (open circuit) when not tuned to a stereo station, and the MONO button is not pressed was measured 23,4 VDC.
When is low (closed circuit) when tuned to a stereo station, and the MONO button is not pressed was measured 0,4 VDC, but no light.
On the diagram, pin 12. should have a voltage of 13 VDC. Do I need to check any of the components on board "A"?

Are we talking about the same bulb? I am working on what I understand to be the "stereo beacon" bulb Supposed to light up when tuned to a stereo station.

I tried the bulb in the AM position, of course I set the switch to AM. The bulb lights up and that means it's working.

The "stereo beacon" bulb should not be lit when the selector is in the AM position. Are you possibly saying that "I tried the bulb in the AM position" means you removed the stereo bulb and put it in the AM socket?

Are you replacing the original bulbs with LED's?

 

[dimitrije.tu]

Yes, that's right, we're talking about the STEREO bulb. She is the problem.

(Are you possibly saying that "I tried the bulb in the AM position" means you removed the stereo bulb and put it in the AM socket?)...
...Yes, I just wanted to test the correctness of the old bulb that was in place of the STEREO. And she is correct.

Yes, I replaced 6 pcs. bulb on the scale with new LED, as well as 1 pc. light bulb on T/S meter with new LED. The new bulbs are 8V, 300 mA. They shine very well.

 

[sregor]

Stereo and indicator bulbs are 50 mA. If you used 300 mA for stereo lamp, will not work right. Other indicator lamps will work ok because they connect to supply and ground, but stereo lamp is connected through limiting resistor (Rk3) and a 300 mA bulb will give low voltage on pin 12.

 

[dimitrije.tu]

Stereo and indicator bulbs are 50 mA. If you used 300 mA for stereo lamp, will not work right. Other indicator lamps will work ok because they connect to supply and ground, but stereo lamp is connected through limiting resistor (Rk3) and a 300 mA bulb will give low voltage on pin 12.

Yes I know it's a 50mA stereo bulb. I have the original one which is working and I have no light on it.
I did not use a 300mA bulb for the stereo lamp.
Rk3 has been replaced and put in a new 330 ohm metal-film resistor.
At the beginning of this post, I wrote what was replaced on board "A".

 

[mrk229]

Yes I know it's a 50mA stereo bulb. I have the original one which is working and I have no light on it.
I did not use a 300mA bulb for the stereo lamp.
Rk3 has been replaced and put in a new 330 ohm metal-film resistor.
At the beginning of this post, I wrote what was replaced on board "A".

Wow it would have helped to know a few of these things up front. It is hard to remote diagnose without clear and complete information.
I can't see or tell what you have done or are doing without very good descriptions or ideally pictures.

If I understand this correctly you have the original incandescent stereo lamp and it works just fine in the "stereo beacon" socket, correct?

You have a new LED stereo lamp that is rated at 30mA and it does night light in the "stereo beacon" socket, correct?

The new 30mA rated stereo lamp lights OK in the AM indicator socket, correct?


That leads me to one conclusion the new LED "stereo beacon" lamp is polarity sensitive.

Can you see how the "stereo beacon" socket is wired?

Can show us a picture of the bulb? What style/type base does it have?

I posted a schematic earlier with the lamp ass'y in it. Pin 1 goes to the "stereo beacon" lamp socket. Exactly where is it connected? Pictures would help.
Knowing the lamp/socket style will also help. The same for pin 12 of the lamp ass'y where is it connected to the socket.

 

[dimitrije.tu]

I must apologize in advance to everyone for harassing you. It was my mistake.
I had to thoroughly check all the components that I installed on board "A" (X00-1770-10).
Everything is done as it should be, except for resistor Rk3.

A local supplier sent me a metal film resistor with a value of 330 kΩ instead of the specified 330 Ω.
I did not control it when I installed it on the board. I was sure it was as it should be.
I replaced it with a new one whose reference value is 330 Ω.
The STEREO lit up.
I would appreciate everyone's help.

The question remains why I have such a difference in voltage on this pin 13 ''C'' (X00-1790-10) ?
- pin 13 shows -1.6 VDC instead of -7 VDC
Can this difference in voltage damage individual components and does it affect the musicality of the receiver itself ?

 

[sregor]

The question remains why I have such a difference in voltage on this pin 13 ''C'' (X00-1790-10) ?
- pin 13 shows -1.6 VDC instead of -7 VDC

Maybe voltages are with receiver not in FM mode? (Goes to pointer so won't affect sound) Try switching to Aux or phono...

 

[dimitrije.tu]

Yes, checked pin 13 on board "C" and flipped the SELECTOR switch. Voltages on AM and FM are -1.6 VDC. Voltages on PHONO1,2 and AUX are - 8 VDC.
That should be right?