Bias adjustment for "click off" on CR-2020

[jdg123]

checking everything as best I can

I cannot get those voltages for you because of the way the two boards are packed in. To operate the receiver the boards must be joined. I could try to rig up some clamps and jumpers to make a go of it but it would take a while. How important is it?

Meanwhile I took some photos marking polarity and noting eareas I have studied for flaws. Of course I can't see any issues but it could be a case of "refrigerator blindness" where you cannot see what's right in front of you

 

[jdg123]

couple more pics

Here are a couple more shots of the electrolytic boards. I have checked the traces for continuity in all places, its fine, even my repairs. There are no bridges either so if the polarity is correct I don't know what the heck is going on.

Also, I have pulled the bridge rectifier (d801)on the electrolytic board and checked it, its fine as are the two main diodes (D806, 804) and too the resistors of the service bulletin. Specs are good. ;-| I can't figure this thing out.

 

[petehall347]

not interested in the big caps just now ..its the 2 1000uf ones for the NB+ NB- ..they are fed from the little bridge rectifier d801 via 2 series resistors for plus volts and same for negative volts NB ..looks like 22ohms fuse resistors and 33ohms ..
you should be able to take voltage readings from the caps around the bridge .

 

[jdg123]

Yes, I can use the legs fo the small film caps for the + and - of the D801 and I maight be able to get a probe in the joint for a reading of the +NB and the -NB.

I won't be able to access the resistors below the joint.

I'll get those reading and then post...

 

[jdg123]

I have a Kline auto-ranging meter and there is an issue about getting a steady reading, further I find by the time I have recorded one or two the resistor you'd like a reading from gets cherry red, starts smoking (I guess as it burns off the flux at its solder joints)

This is sO Bad.

First reading on the plus side of the D801 rectifier = +39volts
Second reading at the +NB= -55volts
Third reading of the neg side of the D801 is only -100mVDC
Had to let things cool...

Fourth reading was of the -NB -100mVDC

 

[petehall347]

it looks like there is a short then . maybe caused by moving stuff around
either that or c806 is in backwards

 

[jdg123]

I can look for raw wire, I have found no bridges. Where do you think this short might exist? Could one of the main caps be a dead short? Please let me know what you are thinking

John

 

[petehall347]

don't suppose you put the 6 pin plug on wrong ?

 

[jdg123]

No I am quite careful about that...

 

[petehall347]

ok something appears to be shorting the NB- ...i cant see any components that could be shorting like that without showing itself ..
c806 appears in the right way round from the pics ..
it has to be a wire shorting or a solder blob .
either that or the resistors have gone very high ohms and just smoking ..
you should be able to see if its shorted with your meter ..power off of course ..

 

[4seatPilot]

picture of the component side of both boards?

 

[jdg123]

component side power distribution

Note in the pics that I have compensated for the half twist in the orentation of TR712 and TR715 with the color coded wiring and that those transistors are insulated from the chassis.

I could not get every cap in the power distribution board in the shot but the lower ones out of sight are as they should be according to the markings on the board...

 

[jdg123]

about the cherry red resistor... I have checked it and it is not a short. Amazingly it still hold tolerance at 56 Ohms.

 

[petehall347]

about the cherry red resistor... I have checked it and it is not a short. Amazingly it still hold tolerance at 56 Ohms.

i meant check NB- to ground

 

[jdg123]

Well now, that is interesting...yes back at post #185 I misnamed the +NB and -NB...

So with that corrected: it is the +NB (the left two pins of the six pin connector) that is shorted to ground.

 

[petehall347]

voltage on tr712 was looking ok ish so +NB wasn't a concern .. voltage on tr715 was bad .so i suspected -NB was wrong .. i still think its what should be looked at .
another thing way back tr711 collector was missing its negative voltage ..it all leads back here ..
do the NB.S not go through wires ? and not the plug

 

[jdg123]

I'm not sure I understand: <<do the NB.S not go through wires ? and not the plug >>

 

[petehall347]

the NB plus and minus .. i have been trying to figure out from your pics if that supply goes through the plug or through wires

 

[jdg123]

OH, it goes through the plug: two leads on the left are +NB, two in the center are "E" and the far right two are -NB...

 

[petehall347]

ok i worked it out .. it could be that tr715 is shorted on the chassis or is wired wrong . i take it that tr715 is one of the transistors on the wires ?