Need help repairing Yorkville MP6

fastvideo · 28th July 2011, 09:21 PM

http://www.yorkville.com/downloads/other/smmp6.pdf

Driver and output components, resistors and diodes all measure good before power on, then output shorted. This is my 3rd times already.

Need some advise.
Anyone can help?

Thanks.

mickeymoose · 29th July 2011, 12:50 PM

I would start by removing the 4 output transistors and R11. Replace R11 with 2 resistors of about 1/2 value, their centre connected to the output rail. Instead of the speaker use a 100 Ohm resistor the load. Than measure the voltages. Good luck! E

fastvideo · 29th July 2011, 03:44 PM

Thank you mickeymoose

following your advise, R11 with 2X20 ohms center to speaker out, measure with no load.

Speaker out close to 0 volt.
The voltage is 4.4v at base of Q11 and -4.4v at base of Q10.
U2 pin1 is 4v, pin7 is 4v.
U2 pin8 is 16.5v, pin4 is -16.5v.
Q7 base 2.5v, collector 3.15v, emitter 4.4v.

I have the vr to min. the voltage between the 2 base is 8 volt.
shouldn't D9, D10, R37, D27 Q7 R38 plus the vr controls the voltage to around 3volt between the 2 bases.

Need more help.

Thank you.

Enzo · 30th July 2011, 01:56 AM

8 volts of bias??!! That ought to burn up your outputs pretty well. They would be running pretty hot, I;'d think. Yes, I'd want to see something closer to 3 volts.

verify the resistance of the R37, R38. You may have to lift them from the circuit to measure. And check the junction voltage drops of the two diodes. But more important, check the bias transistor Q7.

But my main suspect here would be the bias control itself. I can't read the part number. Make sure the little trim pot is not open at either end, and that the wiper works.

You want Q7 conducting harder.

fastvideo · 31st July 2011, 08:43 PM

Problem found, Q7 is defective, which is hidden in the heat sink.

Thank you all from pointing me the right direction.

28th July 2011, 09:21 PM	#1
fastvideo diyAudio Member Join Date: Jan 2005 Location: montreal	Need help repairing Yorkville MP6 http://www.yorkville.com/downloads/other/smmp6.pdf Driver and output components, resistors and diodes all measure good before power on, then output shorted. This is my 3rd times already. Need some advise. Anyone can help? Thanks.

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29th July 2011, 12:50 PM	#2
mickeymoose diyAudio Member Join Date: Nov 2008	I would start by removing the 4 output transistors and R11. Replace R11 with 2 resistors of about 1/2 value, their centre connected to the output rail. Instead of the speaker use a 100 Ohm resistor the load. Than measure the voltages. Good luck! E

29th July 2011, 03:44 PM	#3
fastvideo diyAudio Member Join Date: Jan 2005 Location: montreal	Thank you mickeymoose following your advise, R11 with 2X20 ohms center to speaker out, measure with no load. Speaker out close to 0 volt. The voltage is 4.4v at base of Q11 and -4.4v at base of Q10. U2 pin1 is 4v, pin7 is 4v. U2 pin8 is 16.5v, pin4 is -16.5v. Q7 base 2.5v, collector 3.15v, emitter 4.4v. I have the vr to min. the voltage between the 2 base is 8 volt. shouldn't D9, D10, R37, D27 Q7 R38 plus the vr controls the voltage to around 3volt between the 2 bases. Need more help. Thank you.

30th July 2011, 01:56 AM	#4
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	8 volts of bias??!! That ought to burn up your outputs pretty well. They would be running pretty hot, I;'d think. Yes, I'd want to see something closer to 3 volts. verify the resistance of the R37, R38. You may have to lift them from the circuit to measure. And check the junction voltage drops of the two diodes. But more important, check the bias transistor Q7. But my main suspect here would be the bias control itself. I can't read the part number. Make sure the little trim pot is not open at either end, and that the wiper works. You want Q7 conducting harder.

31st July 2011, 08:43 PM	#5
fastvideo diyAudio Member Join Date: Jan 2005 Location: montreal	Problem found, Q7 is defective, which is hidden in the heat sink. Thank you all from pointing me the right direction.

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