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CR2020 transformer issue?

N

niclasf

New Member
I am working on an auction object (CR2020) that I got cheapish. It sold as a defect.
After troubleshooting for some evenings I now start to suspect that the transformer is broken.
When powering on (using a light bulb protection) the relay never go out of protection mode. After about 10 seconds the protection relay start to make a buzzing sound. It is like it can almost switch on, but not really.
This lead me to check the Power Supply Board BE-BE input voltage.

The voltage between the BE cables when not connected to the Power Supply Board is 12.1V RMS. When I connect them to the Power Supply Board the voltage decreases to 11V RMS. Spec says 17.1V RMS

After the rectifier (D713) I measure 11V RMS (8-12V 100Hz ripple) which seem ok w.r.t. the input voltage (BE-BE)

RE - RE voltage is 41.2V RMS so that seem OK. Spec says 43.2V RMS.

I live in Sweden and I have verified that the mains voltage switch on the back is set correct 230VAC.
I have checked the fuses with a DMM

Could the transformer be broken?
 
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niclasf said:
When powering on (using a light bulb protection) the relay never go out of protection mode. After about 10 seconds the protection relay start to make a buzzing sound. It is like it can almost switch on, but not really.
This lead me to check the Power Supply Board BE-BE input voltage.
Click to expand...
Your dim bulb is loading down the power supply voltages.
 
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@avionic Thanks! Tested without the dim bulb this morning and guess what? It worked!!!
Now fine sound is coming out from the speakers! Adjusting the idling current as I speak.

This was a scary project. For many reasons.
I bought this CR2020 in an auction and I did not have a clue what the status was. Despite this I immediately, without diagnosing did the following,
  • Full recap (except Phono and radio). Several caps on the Power supply board, Main board and capacitor board was short circuited (~5pcs). The capacitors was in a really bad shape. Main caps I measured to 10,000uF (should be 18,000uF)
  • Except for the caps, I also cadded a brand new Capacitor board that handle hight temps better and is adapted to modern 5-pin snap-in capacitors.
  • Changed the broken bulbs (3pcs). Not switching to LED.
  • Applied the SBs
  • Moved and upgraded TR712,TR715 to TIP41C
  • New relay. Old one was missing receiving connector surface.
  • Power switch was broken. Mechanics OK, but the electric switch was totally broken in a plastic bag on the side. I made a plastic bracket with my 3D-printer that holds a microswitch that is triggered by the power switch. Very happy with the result.
  • Cable harnesses between power board and main board was changed to new cables AWG20.
I think that was most of the things.

... after doing all this I tested the amp status :D
I know this is just plain stupid, but I felt sure I could fix whatever problem that would arise. I did this for pure fun.
However, it worked!

Oh, I forgot. The receiver was bought without wooden case, so that is my next project to recreate a nice casing.
 
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