KR-7600 Power Supply Diodes

tinkerer

AK Subscriber
Subscriber
Recently acquired a KR-7600 Receiver that will need the power supply boards rebuilt, and I'm somewhat confused by the diodes on the X00-1770-10 Power Supply Board "A".

Dk1 is listed in the SM as EQA01-24R a 24v Zenor Diode. Crosses to a 1N5252B. What is installed is 2458R which is black and doesn't look like other zenor diodes I have seen. It appears to be the original factory part.

Dk2 is listed in the SM as YZ140 a 14v Zenor Diode. Crosses to 1N5244B. This looks like a typical glass orange Zenor with black band, and appears to be the original factory part. I have not pulled it to look at the markings.

Dk3 is listed in the SM as EQA01-24R a 24v Zenor Diode, same as Dk1. Crosses to 1N5252B. This looks like a typical glass orange diode with black band, but nothing like Dk1. By looking at the foil side solder, this may well have been changed out at some point. I have not pulled it to look at the markings.

Dk4 is listed in the SM as 1S2076 a switching diode that crosses to a 1N4148. This looks like a typical glass orange zenor with light blue band, but evidently is not a Zenor Diode. Appears to be the original factory part. I have not pulled it to look at the markings.

Qk1 has the typical hot spot darkened area on the board.
Qk5 has also been quite hot and the board is darkened around it.
The receiver powers up and relay pulls in pretty quickly at 1.5 to 2 seconds. Seems a little quick.
Receiver seems to play fine, but have only tested briefly. I want to get the power supply boards squared away before I test heavily.

X00-1770-10 Power Supply "A" Voltages
Pin 1: +52.4 VDC
Pin 2: +23.8 VDC
Pin 3: +15.9 VDC
Pin 5: -23.9 VDC
Pin 6: -53.0 VDC
Pin 7: -5.0 VDC
Pin 12: +23.8 VDC
I cannot read what the correct voltages should be on the schematic.

Can someone help me sort this out with the correct diode parts and locations on the power supply boards.

I think I have a handle on the transistors and capacitors.

Will change capacitors and diodes on X00-1790-10 "C" board but leave Dr4 S2HB-20 alone unless it checks defective.

Thanks for the help. Jim
 
X00-1770-10 Power Supply "A" Voltages

(service manual values)
Pin 1: +52.4 VDC (+52V)
Pin 2: +23.8 VDC (+23V)
Pin 3: +15.9 VDC (+13.8)
Pin 5: -23.9 VDC (-23)
Pin 6: -53.0 VDC (-52)
Pin 7: -5.0 VDC (-4)
Pin 12: +23.8 VDC (+13) (is your STEREO lamp burned out, or not tuned to a stereo station?)

You can increase relay delay by installing a 330uf cap at Ck7 - works well

I always lift one end of diodes to test.

Unmolested power supply "A" board for comparison

P1011443.JPG

Power supply "C" - minus the bridge rectifier

P1011445.JPG
 
Last edited:
gort69 that is awesome information, the spec voltages is exactly what I needed. The pics are great also. Really appreciate it.
Someone has changed Dk3. I had planned on changing all the diodes anyway, just needed to know the correct diodes, which you have given me in a different thread.

Stereo light works. If pin 12 is a light it would be AC right? I measured DC. So it has 8.1 VAC on pin 12.

What is the replacement for the S2HB-20 Bridge Rectifier?

Thanks again........Jim
 
Pin 12 is DC, it goes to BEACON, which I believe to be the STEREO lamp. It comes off of the emitter of Qk1 through Rk3 (330 ohm 1W) and straight to pin 12. You must have made your measurement when switched to something other than FM, or not tuned to stereo. Or I could be entirely wrong!

I have used this for the bridge rectifier. Kinda tight to get it installed and the leads have to bent to fit. https://www.mouser.com/ProductDetai...GLxb4p60A2EWWsIa1D7qph0Opjsva8e5xHzRfLmF7Xw==
 
One more question if I might. Rk4 on my board is 220 ohm, looks original but the board has been previously worked on and it's a mess in that area. Schematic shows 220 ohm, but the parts list says 390 ohm. I'm pretty sure it's 220 ohm but just wanted to confirm. Can't see it in the pic.
Thanks
 
Back
Top Bottom