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Old 6th May 2012, 02:53 PM   #1
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Default No Right ch sound on yaqin mc10l

Hi,
I need some help with my mc10l no right ch sound.
I have debugged and isolated down to the right ch preamp section by doing all the cable swap tests. Input selector and vol pot is also ok. Output transformer and the push pull stage is also ok.
On the look side, all the tubes looks normally lighted.
No wire wiskers of sorts on or below the pcb.

Any help will be greatly appreciated.
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Old 6th May 2012, 02:59 PM   #2
DF96 is offline DF96  England
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Measure DC voltages.
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Old 6th May 2012, 07:50 PM   #3
Hi_Q is offline Hi_Q  England
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This might help you if the layout is the same.
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Old 7th May 2012, 06:37 AM   #4
atsc is offline atsc  Australia
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Have you tried swapping tubes between sides? Mine is still working and sounding sublime (touch wood) after more than 6 months...
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Old 7th May 2012, 04:23 PM   #5
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Thanks for the schematic with the reference voltage to look out for.
I've measured and found that R205 is in high impedance.
This 33K resistor does look very normal on my board thou, no burn marks whatsoever, Don't understand why it did fail.
My V4 tube was lighted thou.

1.8V wasn't present at R202 too.
R217 was measured to be 47ohms only. is the ESR of the cap in parallel playing an effect?

I shall be changing the R205 first.
Anything else should I look out for?
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Old 7th May 2012, 09:52 PM   #6
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Quote:
Originally Posted by Obession View Post
R217 was measured to be 47ohms only. is the ESR of the cap in parallel playing an effect?

Anything else should I look out for?
you re just measuring the 47R resistor that is in parallel with it (the cathode resistor). So it s normal.
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Old 8th May 2012, 01:16 AM   #7
Hi_Q is offline Hi_Q  England
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Don't forget that some easy checks can be made without removing any covers. With respect to the attached table, you can go round the input tube sockets with your multimeter - with the Amp switched OFF of course AND allow plenty of time for any high voltages to discharge! Start by pulling V1 and V2 to check the Left Hand Channel, then V4 and V3 to check the right.
Remember that the tube socket numbering is now reversed as you are looking down onto the top, therefore the socket numbers go 1 to 9 counter-clockwise from the space. You may have to use some suitable single core wire to connect to the sockets if your multimeter probes are too thick.
Test 1 checks V1/V4 cathode circuit
Test 2 checks V1/V4 input circuit
Test 3 checks V1/V4 link
Test 4 checks V1/V4 1k Resistor
Test 5 checks V1-V2/V3-V4 link
Test 6 checks V1-V2/V3-V4 Anode Loads
Test 7 checks V1-V2/V3-V4 Anode Loads
Test 8 checks V2/V3 1M Ohm resistors
Test 9 checks V2/V3 link
Test 10 checks V2/V3 LTP Cathode Resistor

The readings taken as 'actual' were from a fully working amp.
Les
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Old 9th May 2012, 03:58 PM   #8
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changed the 33k and it did the trick to restore my right Ch.
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Old 9th May 2012, 05:05 PM   #9
Hi_Q is offline Hi_Q  England
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Well done.It can happen sometimes with film resistors. Showing no obvious sign of failure was good in some way as otherwise a burnt resistor would have indicated other problems
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Old 9th May 2012, 05:27 PM   #10
Hi_Q is offline Hi_Q  England
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Well done.It can happen sometimes with film resistors. Showing no obvious sign of failure was good in some way as otherwise a burnt resistor would have indicated other problems
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