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Old 28th Nov 2023, 4:34 pm   #1
Dick Glennon
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Default Bush DAC90A low volume.

Hi again, I have a Bush DAC90A with very low volume. I am working the FM to AM converter. The stations are very clear but very faint. The valves are all OK.and all capacitors have been replaced except electrolytics. Any thoughts would be very much appreciate.

Regards, Dick.
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Old 28th Nov 2023, 4:50 pm   #2
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Default Re: Bush Dac90A low volume

Is it only the station you picking up from the FM converter that's low or broadcast stations (the few that there are ) as well?

Cheers

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Old 28th Nov 2023, 4:53 pm   #3
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Default Re: Bush DAC90A low volume.

Does it work in normal mode? I appreciate there might not be much to listen to in Ireland.

How do voltage readings compare with the service sheet?
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Old 8th Dec 2023, 7:31 pm   #4
Dick Glennon
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Default Re: Bush DAC90A low volume.

Hi again, I finally got round to taking voltage measurements on the DAC90A.V1 pin 2 78(98) pin3 42.7(47) pin5 42.5(47) pin7 .57(.8) V2 pin2 78(74) pin5 42.5(47) pin7 .86(1.0) V3 pin 2 38(74) pin7 .86(1.3) V4 pin2 158(190) pin5 78(98) pin3 3.6(5) V5 pin2 180(222) pin7 172(205) .Mains voltage is 230volts. Hope this may shed more light on why I have such low volume. Regards Dick.
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Old 8th Dec 2023, 7:45 pm   #5
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Default Re: Bush DAC90A low volume.

The voltages and currents seem to be low.

Can you measure resistance of the heater dropper resistance, the section nearest the heaters.
Do the same for the cathode resistor of V4.

When you power it up, can you measure the voltage across them and then calculate the current through them.
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Old 8th Dec 2023, 8:20 pm   #6
gallowfields
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Default Re: Bush DAC90A low volume.

Also check that the secondaries of the IF coils are not open circuit or the tuning capacitors to them. I have had a few instances of both, the silvered micas are 112pF

Regards, Brian.
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Old 11th Dec 2023, 8:00 pm   #7
Dick Glennon
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Default Re: Bush DAC90A low volume.

Hi again,there have been capacitors and resistors replaced in the Dac90A. I happen to have both the trader sheet No 1161 and the bush original service sheet. The capacitors and the resistors in some cases do not correspond with each other in the under body visual e.g C 15 (Trader) =C14 (Bush) This has been repeated with both capacitors and resistors. I am wondering if one or both of those sheets were used in replacing the old capacitors and resistors. Which sheet should I check with. Dick.
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Old 11th Dec 2023, 8:19 pm   #8
gallowfields
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Default Re: Bush DAC90A low volume.

Best to forget about the difference in circuit references numbers and just visually check the components [if suspicious] for value etc. Although your voltages are a little low I wouldn't worry too much about that at present. Check the waveband switch has clean contacts and also check the secondary windings of the IF transformers. Surpringly they can still work with an open circuit coil but perform with very low volume.
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Old 12th Dec 2023, 10:46 am   #9
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Default Re: Bush DAC90A low volume.

Quote:
Originally Posted by Dick Glennon View Post
Hi again,there have been capacitors and resistors replaced in the Dac90A. I happen to have both the trader sheet No 1161 and the bush original service sheet. The capacitors and the resistors in some cases do not correspond with each other in the under body visual e.g C 15 (Trader) =C14 (Bush) This has been repeated with both capacitors and resistors. I am wondering if one or both of those sheets were used in replacing the old capacitors and resistors. Which sheet should I check with. Dick.
It doesn't matter which service sheet you use, but when referring to component designations, such as Cnn or Rnn, here make it clear which service sheet you're using so that members responding to your post know which component you're referring to.

Let's all sing from the same hymn sheet!
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Old 12th Dec 2023, 11:01 am   #10
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Default Re: Bush DAC90A low volume.

Quote:
Originally Posted by Dick Glennon View Post
V5 pin2 180(222) pin7 172(205). Mains voltage is 230volts.
I'd concentrate on why the AC voltage on V5 anode pin 2 is so low. Check the setting of the mains voltage selector, the resistance of the dropper sections R15, the surge resistor R17 and the resistor across the scale lamps R16. Component references are from manufacturer's service sheet.

It's always best to check things which can be measured and are obviously wrong first.
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