Adcom GFA-535 blowing main power fuse - diyAudio
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Old 30th July 2015, 11:59 PM   #1
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Default Adcom GFA-535 blowing main power fuse

As stated main fuse popped when plugged back in after having it unplugged for sometime. I looked it over very closely and everything looks good from what I can see. Anyone have any info on what to check and how to check transformer and rest of power supply with meter without running any power. Thanks for any advice.
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Old 31st July 2015, 01:23 AM   #2
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I would start by disconnecting amp from its power supply.
Then check voltage across smoothing capacitors if turning it on doesn't blow fuse. Or even just check AC on transformer secondaries.
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Old 31st July 2015, 08:49 AM   #3
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Try lifting the fuses, that will disconnect the power amplifiers then work backwards towards the power in. After checking the transformers are OK.
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Old 31st July 2015, 04:02 PM   #4
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Quote:
Originally Posted by JonSnell Electronic View Post
Try lifting the fuses, that will disconnect the power amplifiers then work backwards towards the power in. After checking the transformers are OK.
Adcom GFA 535 has four 4A fast blow fuses on the two +/-50V rails powering the independent power amps. Lift them as suggested above and use a 40 W lamp trouble shooting assembly to determine if the power supplies are OK, and also to save future AC fuses from blowing; fuses are expensive. I faced a problem like this with a Radio Shack receiver. A power rectifier in its power supply [+/- 60V] was shorted and thus channeled AC from the secondary winding of the power transformer through the 8600 uF capacitor to ground; which was a dead short. If the 40 W bulb lights up, turn power off immediately as the power supply capacitor or other entity will/may get damaged.
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Old 31st July 2015, 06:54 PM   #5
sonidos is offline sonidos  United States
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BZ,

If this is the 535 and not 535II, send me a PM so I can send you a scan of the service manual. It will help.
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Old 31st July 2015, 06:59 PM   #6
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Thanks. I will try it tonight. I will post my findings. Hopefully it is something small and not the transformers.
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Old 1st August 2015, 11:11 AM   #7
AndrewT is offline AndrewT  Scotland
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the 40W light bulb is a very good suggestion. Build a Mains Bulb Tester.

If the bulb does turn on and stay on, then usually nothing gets damaged, not even the fuse/s. The bulb drops so much voltage that the mains input to the amplifier/transformer is down around 5 to 10Vac and the secondaries are down proportionately.

The Mains Bulb Tester lets you measure voltages around the transformer. But take care the system is still connected to LIVE.
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Old 4th August 2015, 07:12 AM   #8
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Still blowing fuse . I'm going to have to start taking it apart piece by piece and check everything with back up power supplies. any in put will be good. Thank you.
Also some one said they posted a complete rebuild of one and I could not find it. That would be a big help. Thanks again................
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Old 4th August 2015, 08:04 AM   #9
AndrewT is offline AndrewT  Scotland
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I suggest repeatedly that every build should be checked for correct operation in stages via a Mains Bulb Tester.

Transformer power up alone is the FIRST STAGE.
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Old 4th August 2015, 06:49 PM   #10
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Dim bulb tester is the tool needed. Then you start disconnecting power to different sections of the amp till the lite goes off. You've located the area of the problem and start checking components... However something that takes out a 4 amp fuse has to be a part that can pull 4 amps without burning up. Maybe with the dim bulb tester glowing you can feel what's running hot, disapating all that power....
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