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.
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.
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.
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.
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.
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.
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-1-203lf/trimmer-20k/dp/9354140
http://uk.farnell.com/bourns/3329h-1-203lf/trimmer-20k/dp/9354140
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.
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.
for the last few times i have used these capacitors,
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5330609#header
these are from rs components, not farnell although they might sell similar.
when you put these things on you need to be very careful that the leads DO NOT TOUCH THE CASE, i would recommend you cover them with something, such as the rubber shroud that covers the live and netural wires in twin and earth.
also so i send you the right manual, where on the circuit board are the 2200uf caps, if your looking from the front are they in the left hand corner, or are they in the middle of the board?
thanks
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5330609#header
these are from rs components, not farnell although they might sell similar.
when you put these things on you need to be very careful that the leads DO NOT TOUCH THE CASE, i would recommend you cover them with something, such as the rubber shroud that covers the live and netural wires in twin and earth.
also so i send you the right manual, where on the circuit board are the 2200uf caps, if your looking from the front are they in the left hand corner, or are they in the middle of the board?
thanks
mine too has power caps in the middle of the board (3020A?)
do you have the right manual? impossible to find it on the net
thanks
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