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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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20th May 2022, 11:10 pm | #61 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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Re: Pioneer qx-8000 : capacitor or transistor problem?
Don't like co-incidences, try lifting one end of R6.
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23rd May 2022, 3:48 pm | #62 |
Tetrode
Join Date: Jan 2020
Location: Ilkley, West Yorkshire, UK.
Posts: 92
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Re: Pioneer qx-8000 : capacitor or transistor problem?
OK, progress. I took out Q2 and checked for any shorts between the connection for it and there were none. So I found a BC337 and put it in and checked the voltages on the base of Q1 and it was 13.2v which seems about right. The emitter of Q2 was 33.2v. So I resoldered in the resistors to reconnect the outputs but left the boards powered from B2 still not connected. The results were :
B1 : 54.8 B2 : 33.2 B3 : 22.4 B4 : 22.6 B5 : 11.7 B6 : 33.2 So now too high on B2 and B6! Measuring around Q1 and Q2 : Q2 53, 33.2 , 33.8 Q1 13.2, 12.6, 33.8 |
23rd May 2022, 5:21 pm | #63 |
Heptode
Join Date: Jan 2011
Location: Croydon, London, UK.
Posts: 773
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Re: Pioneer qx-8000 : capacitor or transistor problem?
The output voltage of the regulator is about right now. The exact voltage will depend on the exact values of the potential divider resistors, the Zener diode and the VBE of Q2. What you have seems reasonable.
Without a load, the voltage on B2 will be too high. Once the external load is connected, it will drop to the correct level. It looks like you have repaired the fault, so well done on your persistence! Paula |
24th May 2022, 8:34 am | #64 |
Tetrode
Join Date: Jan 2020
Location: Ilkley, West Yorkshire, UK.
Posts: 92
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Re: Pioneer qx-8000 : capacitor or transistor problem?
More well done to you for persevering with me. I guess I was fooled by the fact that the original Q2 tested fine.
Many thanks. I will now get on with re-capping the other boards. |