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MX110 - Smoke on 220ohm resistor after recapping

J

joss2178

New Member
Hi,

Bought a MX110 3 weeks ago - I never turned it on - and I just finish recapping it.

I first started it with a Dim Bulb Tester and everyhting was working fine. Then went without. One of the 220ohm white resistor near the electric plugs started smoking (Pretty sure it is R152 - it is between the other 220 and the big browns one).

I recapped all 3 cans, all with single caps.
Recapped the 10uf and 12uf.
Recapped both 1uf at c106,107.
Replaced the selenium bridge with 4 SF4007 diodes.

Ordered a MF72-47D20 47ohm 3amp thermistor.

I read that I should put a resistor after the bridge. What value ? In serie between D11,12 and anode of c114 ?

Will/should it fixes my smoking resistor problem ? That resistor is measuring about 210, should I change it ?

Did some fast measurement, my line voltage is 117volt.
For the test point :
225volt > 254volt.
170volt > 199volt.
155volt > 172volt.
108volt > 120volt
83volt > 100volt
(I think I measured at the good place but do not want to turn it on again for now)

So it looks like I am pretty high.

btw my multimeter is true RMS
 
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Hmm, by looking more deeply in the schematic, I understand that this resistor (R152) is going to the v11 6U8 (MPX Amp). The 6U8 tube currently installed is all smokey inside - it was already like that when I got the amp, so I ordered a new one that I have in hand - should I tried the new tube, or it will get smoke?
 
Ok - found part of my problem, will not be able to troobleshoot more before this weekend.

So I follow the path of the 108v and saw a resistor a bit burn - the 6.8k at R31 - gonna have to test it. So I removed the 6CS6 at V7 and no more smoke. Hopefully, this is not a chain reaction and my problem stop there. But I really hope it is not the transformer T4 that seems related to it. How would I test if T4 is ok ? If R152 was smoking and R31 seems burned, any idea where the problem would be ?


At least, for now, the problem is on the radio side, so I am still able to test everything not radio related.
 
So the R31 resistor was ok.

I looked all around the 6CS6 V7 for any short-circuit, did move a bit the resistors and capacitors to make sure they were not touching anything - but beside a wire lightly damage. Restarted and now it is not smoking anymore. So not really sure what it was.
 
I'd probably replace tube associated with that circuit and call it good. That tube should be knock-checked for shorts in a good tester.​
 
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