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Old 30th March 2009, 06:21 AM   #1
jerryo is offline jerryo  Isle of Man
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Default Another NAD 3020

I have just pulled out an old 3020 from a shelf where it has been hiding for awhile.
On switch on there is a thump and crackle which seems to be quite common, but that quickly dies away.(caps charging)?
Both channels work but one set of speaker outputs has some voltage across them which cannot be adjusted. I tried both trim-pots; VR6 is fine but VR5 has no effect from full left to full right.
Please can someone point me in the right direction for diagnosis.
Would like to repair otherwise its going for spares or repair on ebay.
Many thanks.
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Old 30th March 2009, 07:02 AM   #2
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Do you have a copy of the service manual?

dave
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Old 30th March 2009, 08:29 AM   #3
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the thump on switch on is normal with these amps, as there's no protection circuit.

the crackle is the power switch i have replaced many of these, when replacing also replace the capacitors on the switch.

this is quite an old amp, so other things inside will need replacing most if not all capacitors gone, while replacing these is not expensive, i would recommend useing all the same make on all but the signal caps, for this you will need the service manual or schematic.

the reason why one of your pots won't adjust is that it is broke, you will not find anys pots this big, so find the biggest you can and extend the legs so it does fit, the value of these pots is 20k.

something else thats worth noting, if the voltage on the terminals is around 5v and you have'nt replaced the the capacitors on the board, its a good chance that the 1000uf 6.3v cap has gone in that channel.

and finally if this amp hasn't been looked at for a few years or ever, the idle current will need adjusting, again instructions for this are in the service manual.
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Old 30th March 2009, 08:54 AM   #4
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Quote:
Originally posted by reddish75
you will need the service manual
http://p10hifi.net/planet10/manuals/...viceManual.pdf

dave
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Old 31st March 2009, 07:24 AM   #5
jerryo is offline jerryo  Isle of Man
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Thanks for the quick replies, very good of you.
Planet10, I have tried the link to the service manual but it just comes up with a blank page. I will try again but if that does not work do you know if there is another site that has it?
Reddish75, the amp is showing 0.648 volts across the speaker terminals of one channel if that helps in any way. I thought about doing a cap re-placement some time ago, that`s when it went on the shelf so maybe it is time. What about reducing the switch-on thump...........any ideas (simple ones).....what about a couple of correctly rated thermistors on the supply rails to the power amp section before or after the fuses?
Thanks again.
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Old 31st March 2009, 07:59 AM   #6
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Quote:
Originally posted by jerryo
Planet10, I have tried the link to the service manual but it just comes up with a blank page.
Works fine here. Have you tried to download it to your desktop or are you trying to open it in your browser?

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Old 31st March 2009, 09:22 AM   #7
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the new switch and capicitors across it should reduce the thump, the only way to remove it completly is buy or build a speaker protection relay, as for the voltage it could be just down to the broken pot, replace this part before you do anything else just to see if it is.

thanks

chris
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Old 31st March 2009, 01:06 PM   #8
jerryo is offline jerryo  Isle of Man
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Hi planet10, have got it now so thanks again. Cheers dude.
Hi reddish 75, there is some choice of trim-pot from Farnell; would a rating of 0.5w be OK? it does not give a figure on the parts list.
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Old 31st March 2009, 11:53 PM   #9
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i use these you can bend the back legs to fit without extending then, so just the front one to do!

http://uk.farnell.com/bourns/3329h-1...20k/dp/9354140
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Old 1st April 2009, 05:40 AM   #10
jerryo is offline jerryo  Isle of Man
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Hi reddish75, those are the ones that I was looking at myself. I will do both of them (vr5,vr6) of course.
The service manual from planet10 gives a different layout to the amp that I have and has another trim-pot (vr7) for setting the output display led`s. I need to have a close look to check whether the instructions given for setting the idle current still hold true by using R653,R654.
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