CR-3020 Amp board problems

[ecluser]

Check the two 10 Ohms-5W resistors on the Protector circuit board. It is normal that the protector relay is open at power-ON. The charging current in the large capacitors is limited by the 10R-5W resistors. When the voltage reaches approximately 80% of the final voltage, the relays close to complete the charge. If you have no voltage at the bridge rectifier, it is probably because the 10R-5W resistors are open.

 

[kcvintage]

I'm still here just took a break!

Doing some PS work - I did have the relay activating but now I need to replace the 1D4B-1 bridge rectifier. Looks like similar/identical to 1.5A 400V WO4M. Looks like this one will work?

https://www.mouser.com/ProductDetai...ductor/W04G-E4-51?qs=D6r9GjgEnNO6smGLjWlqbg==

 

[avionic]

Should do the job. Is the old one bad ?

 

[kcvintage]

Yes. I shorted it. Not sure how but I suspect testing off of the DBT - I think there was a PS wire off that I didn't know about and it shorted to the wrong wire wrap terminal. I'm tempted once I get it working to replace all these wire wrap terminals with these:
https://www.mouser.com/ProductDetail/Keystone-Electronics/5115?qs=do/%2B0R7m72eN44oti49NVg==

 

[avionic]

I'm tempted once I get it working to replace all these wire wrap terminals with these:

I wouldn't even molest the wire wraps. Wire wraps are a better connection than solder !!!

 

[kcvintage]

Still dealing with the power supply...
Need to replace TR701 and 704, complementary pairs 2SC1913 and 2SA913. Research on AK and comparing datasheets indicates best bet for what is currently available would be 2SC5171 and 2SA1930. Do you have experience with this sub? Thoughts? Thanks again!

 

[Sparkplug]

Still dealing with the power supply...
Need to replace TR701 and 704, complementary pairs 2SC1913 and 2SA913. Research on AK and comparing datasheets indicates best bet for what is currently available would be 2SC5171 and 2SA1930. Do you have experience with this sub? Thoughts? Thanks again!

Going only by the specs, yes 2SA1930/2SC5171 should work fine.

 

[kcvintage]

I have the two new transistors (above) installed, and have replaced caps in this section of the board. Any ideas as to why the +b voltage is 72.4 and the -b voltage is -86.5?

 

[avionic]

What is the BCE voltages on TR701 and TR704 ?

 

[avionic]

The collectors should be +/- 79 to 80 vdc.

 

[kcvintage]

I have the exact same voltages for the b, c and e of each transistor:
TR701B, C, and E: 70.5 v
TR704B, C, and E: -86.9 v
I've checked/replaced TR702 and TR703, replaced D701, D702, D706 and D707. Also, several of the resistors have been replaced with metal film. Capacitors also new.

I believe you are a veteran? If so, thank you for your service.

 

[avionic]

TR701 B, C, and E: 70.5 v
TR704 B, C, and E: -86.9 v

Are these new parts ?

I believe you are a veteran? If so, thank you for your service.

Yes. I spent to much time in that Saudi Sandbox..

 

[kcvintage]

lol.
these are new - allegedly Toshiba and have the Toshiba logo. I bought from an ebay american seller. I wonder about them.

 

[avionic]

Have you tried retesting them out of circuit ?

 

[avionic]

What did you replace TR702 & 703 with ? I'm assuming you checked that all those electrolytics have be properly installed.

 

[avionic]

Need a component side photo of this portion of the power supply..

 

[kcvintage]

I used KSA992FTA for TR702 and TR703. Found a pair within 5 hfe - I am more familiar with matching diff pairs on Marantz amp boards. Should these supply hfes be matched? May want to order some '992s with the higher B gain code? I did check all the electrolytics.

I removed TR707 to test it - tested ok.

With TR707 out I measured the +-b voltages and they were closer to spec (-80.5 and +78.4) but this voltage appears at each of the leads on TR701 and TR704 - same issue as before.

I've attached a picture of this area.

 

[kcvintage]

Have you tried retesting them out of circuit ?

I tested a few of the 4 each remaining I bought, and they each tested good. Did not pull the ones from the board.

 

[avionic]

Should these supply hfes be matched?

No.

but this voltage appears at each of the leads on TR701 and TR704 - same issue as before.

You do realize that the difference between the emitter and base voltage of TR701 & 704 is only .7 volts and the difference between the collector and base is less than 3 volts.. Are you positive your seeing the same exact voltage on all the pins ?

 

[avionic]

Did not pull the ones from the board.

They now might be shorted