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Bias on MC 2205

aedaza said:
Hi guys!
Trying to tackle the power guard lights in the front (green and red) as they are not turning on.
Measured pins from 1 to 10 in the lamp pc board (according to service manual positions).

1-> 0.8 mv
2-> 1.6 mv
3-> 38 mv
4-> 29 mv
5-> 1mv
6-> 5.1 ac
7-> 2.3 v
8 -> 5.1 ac
9-> 0.4 mv
10 -> 0.4 mv

Hope my assistant ( my dad LOL) notted them OK


The bulbs show a small resistance. Meassured 3 in the 200k ohms scale. Cleaned too the ribbon cable socket with electronic cleaner. I remember there are some diodes in the power supply that are part of the lights. Could they be the problem? I ordered replacement 1n4004 for D302 and D303 and have them in hand.

Thank you all
Alejandro
Click to expand...
You need to replace the two 2200uf caps as well.
 
Diode on the lamp PC board are not the problem. Diodes on the PS board possibly, but not likely.

As John said above the two 2200 uF capacitors on the PS board might need to be replaced. The comprise a voltage doubler and if they're bad, the lamp drivers won't work. Check the voltage at the negative side of C308, it should be -11 or -12 V. If that's OK, check continuity on the ribbon cable between each board. As I recall there's a black wire that comes from the lamp PC board that slides onto a spade lug on the chassis. Make sure that's connected.

Do the watts/dB/hold lights work?
 
w3jn said:
Diode on the lamp PC board are not the problem. Diodes on the PS board possibly, but not likely.

As John said above the two 2200 uF capacitors on the PS board might need to be replaced. The comprise a voltage doubler and if they're bad, the lamp drivers won't work. Check the voltage at the negative side of C308, it should be -11 or -12 V. If that's OK, check continuity on the ribbon cable between each board. As I recall there's a black wire that comes from the lamp PC board that slides onto a spade lug on the chassis. Make sure that's connected.

Do the watts/dB/hold lights work?
Click to expand...
Yes! The watts db hold lights work.
Ok I will check continuity on the ribbon+ voltage on C308. Thanks!
 
Hi guys
So I managed to finally pull the knobs as they were stuck due corrosion and take off the faceplate.

2 of the bulbs were out but some cleaning did the trick and I have them ok now.

Don't know what to use to paste again the blue plastic part. Any other suggestions on what is the usual maintenance in this part?

Still have to work on fixing the green indicator lights

Thank you all

1000052594.jpg
 
w3jn said:
Diode on the lamp PC board are not the problem. Diodes on the PS board possibly, but not likely.

As John said above the two 2200 uF capacitors on the PS board might need to be replaced. The comprise a voltage doubler and if they're bad, the lamp drivers won't work. Check the voltage at the negative side of C308, it should be -11 or -12 V. If that's OK, check continuity on the ribbon cable between each board. As I recall there's a black wire that comes from the lamp PC board that slides onto a spade lug on the chassis. Make sure that's connected.

Do the watts/dB/hold lights work?
Click to expand...
Hi @w3jn just checked voltage at neg side of C308. Got 13.7v. Also just in case, replaced D302 and D303 with 1N5395. Also checked for contnuity on the ribbon cable and tightened the screws that seem to do a ground connection. Still no green lights... Maybe they are simply bad?
 
Most likely. They’re on all the time except when the power guard lamps light so they get a lot of hours.
 
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Hi guys!
Just wanted to share you guys I'm stretching this bad boy at my listening room, comparing it to my other standing standard Sansui AU D11 + Kef LS50s. So far, I like what I am hearing!!
Did not expect this result, I don't know... But more natural sounding the MC and more natural highs. Maybe the Sansui has a more controlled bass, but it is going to be a tough choice... Leaning now to the Mc.
 
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