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Old 26th December 2012, 12:02 PM   #611
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John, I advised you to verify your build this way:

1 - remove the fuses from the on-board fuseholder (disconnect the backend) , connect the frontend-transformer (2 x 34 VAC) to the bulb-tester
and switch power on.
Do all LEDs shine? If not: review your build.
2 - If Yes: remove the frontend-transformer from the bulb-tester and connect it directly to your mains.
Connect the bulb-tester between the backend-transformer and your mains and switch power on.
Is the backend-PSU working correctly (showing correct voltages)?
3 - Insert fuses into the fuseholders, keep the backend-transformer connected to the bulb-tester, verify that the potentiometer is preset to 0 Ohm
and switch on power again.


Best regards - Rudi
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Old 26th December 2012, 01:54 PM   #612
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John, you need to find out why the LED's in the front of the amp are not glowing, maybe they are installed back to front. I would put the bias control on zero ohms untill you resolve the LED problem.

The resistor that is overheating is R25? (Roender's original description) and it connects input "cold" to zero volts. This seems ominous, and could indicate that you have instabiity issues. Post 1117 has something to say about this particularly if using NJL3281/1302 devices.

Not certain that I follow your sequence of powering operations. In the third sentence when you say-" switch frontend on 2x25V" etc do you mean switch back end supply on?

Where is the 36mV being measured? It seems to me that the bulb is no longer needed for the front end shunt reg'. Maybe you need to verify that the currents in the front end of the amp are correct, the 1mA and the 13.5mA. If you measure the DC voltage across R20 (1.2K) and apply some Ohms law you should be able to confirm the 1mA. I measured 1.32V here on one of my amps. Similarly, measuring the drop across R19 (91 ohms) will confirm the 13.5mA. It should be around 1.23V

Keith
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Old 26th December 2012, 02:06 PM   #613
lucylu is offline lucylu  England
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Rudi All led s do not shine ,,,red and green next to 4 block connector off ... john
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Old 26th December 2012, 02:35 PM   #614
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Keith Resistor r28 (10r) only overheats when i increase bias control from zero upwards a little,,,,,,,36mv is taken as manual states from measuring points on both q27 and q25.....All led s do work not all at once ................. thanks john
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Old 26th December 2012, 02:50 PM   #615
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John, is your backend-transformer correctly connected to the PCB?
What brand is your transformer?

Have a look at my build and compare the colours of the transformer's leads.

The orange and red leads connect to the AC-poles of the 4-pole connector,
the black and yellow leads connect to "GND".

Rudi
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Old 26th December 2012, 02:50 PM   #616
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John, I didn't realise you were talking about LED's on the shunt regulator. It seems Rudi has some extra LED's that I am not in a position to comment on. Likewise measuring points q27/q25 do not mean anything to me. So without Rudi's manual I am a bit limited in the advice I can supply. Sorry for any confusion I may have caused.

Keith
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Old 26th December 2012, 05:48 PM   #617
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Rudi Transformer 2 x 25 160va Airlink Transformers ltd......am sure its connected correctly but i could be wrong,,,,,,,,,,,,,if i switch on 2 x25v transformer only then both led s red/green come on........Have i misunderstood you
Something is wrong when i switch both transformers on all leds on except green one next to 4 block connector and i hear buzzing sound, ,,,,,,,,,, time for a drink (tea) thanks rudi regards john
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Old 27th December 2012, 07:28 AM   #618
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John, the image that you posted is very irritating, and you connected the transformer to the 4-pole PCB-connector in the wrong way.

Please disconnect your transformer from the 4-pole connector, wire the black and yellow lead together and measure the AC voltage
between the red and the orange wire.
Your DMM should read about 50 VAC.

If so: connect the transformer to the 4-pole connector as shown on the attached image.

Best regards - Rudi
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Old 27th December 2012, 08:53 AM   #619
lucylu is offline lucylu  England
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Default Dam it

Rudi i understand ,,,,i was following the pcb image . you must get frustrated .,,,,,,,,,,,,,,,,,,ok .
When i switch power on to shunt all led come on but not the red and green next to 4 block connector.
Then i switch power on to 4 block connector red and green led come on .....so all leds on,,, all looks ok,,, But 5 sec later resistor r28 (10r) starts to smoke,,,,,, i switch off john
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Old 27th December 2012, 09:11 AM   #620
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@Keith: I added two LEDs to the +/-35 VDC power rails in my layout signalling the status of the backend - power supply.

Best regards - Rudi_Ratlos

P.S.: John - I sent you an EMail.

Last edited by Rudi_Ratlos; 27th December 2012 at 09:14 AM.
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