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Old 26th September 2012, 09:07 PM   #11
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Quote:
Originally Posted by RS232 View Post
You can't measure the capacitor in the board.
You need a capacitance meter and remove the caps from the board.
He only needs an identifiable place to measure the rail voltages, not the capacitor quality. If he can't access the main cap solder pads, then other points are possible.

There are only 2 terminals on a cap and 2 probes to measure with - what's the problem, misfits?
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Old 26th September 2012, 09:13 PM   #12
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I bought it second hand in mint condition 80 one week ago,it was palying great,
my mistake to open the cover..
I hope that the service won't cost much

Cheers guys
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Old 26th September 2012, 09:18 PM   #13
RS232 is offline RS232  United Kingdom
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Around 15 years but depending on series up to 30 years
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Old 26th September 2012, 09:21 PM   #14
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by morinix View Post
How old is this amp?

Could easily be 30yrs, and even in their first decade were well known for living on the edge of reliability of the "bean counter approved" parts used throughout

There was at one time a cottage industry of DIY mods and tweaks that among other things included replacing all EL caps in the PS filters and elsewhere, and hardwiring the pre-power jumpers

This could get me into some trouble, and this is coming from a guy who owned many of the early 3000 and 7000 series amps/receivers, but as much of a giant killer as this was "in the day" (circa early 80s), unless it's a very simple repair, or you're looking to retain the surprisingly decent phono stage, or some of the other features, it could very likely be surpassed in performance and reliability by any of a number of current digital amps - either kit or prebuilt
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Old 26th September 2012, 09:48 PM   #15
morinix is offline morinix  United States
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Ok since the amp is that old my crack guess is the reservoir caps c508 and c509 are going south. They were in the beginning, that is why the hum started. Now that they had to deliver a big transient when you shorted to ground they are near total death. Need to replace them. You will notice new found detail after those are new. A dc measurement may not really tell you the whole story. Still though the 8-4 switch may be at least damaged too but I would look really hard at those caps and address them first then worry about the switch.
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Old 26th September 2012, 10:02 PM   #16
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by morinix View Post
Ok since the amp is that old my crack guess is the reservoir caps c508 and c509 are going south. They were in the beginning, that is why the hum started. Now that they had to deliver a big transient when you shorted to ground they are near total death. Need to replace them. You will notice new found detail after those are new. A dc measurement may not really tell you the whole story. Still though the 8-4 switch may be at least damaged too but I would look really hard at those caps and address them first then worry about the switch.

just be very careful when desoldering from the PCB - traces were notorious for lifting at eyelets - solderwick and suckers and careful prying of any folded over leads


if you do venture on this, it probably wouldn't hurt to find a schematic for the particular model - and be aware that over the life span of the 3020 family there were many revisions, there's a chance that any schematic you find might not exactly match your unit
that made for fun for the warranty departments, let me tell you
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Old 26th September 2012, 10:05 PM   #17
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Is there a chance that the problem might be somewhere else?
I mean since i was probing on the switch the "damaged area" is somewhere around there?
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Old 26th September 2012, 10:09 PM   #18
RS232 is offline RS232  United Kingdom
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I just finished repairing a Cambridge Audio with a toasted transformer (I could see a spark in the transformer) and is now playing Freddy Mercury.
Going to have a look at my 3020i that have a small noise on power up, not the normal thump you have on power up but a noise like the discharge of a capacitor that goes from one speaker to the other.
Another thing in my model 3020i does not have the jumpers from pre to power amp.
About your short it depends how you shorted it
I personally don't see how this can cause any problem to the transformer if it was just a momentary short or else you would have blown the protection fuse

Last edited by RS232; 26th September 2012 at 10:35 PM.
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Old 26th September 2012, 10:51 PM   #19
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I removed the PCB, the capacitors are ok
I noticed that Q508 gets overheated and it was touching the C523 capacitor which had a small mark on it (maybe from the heat).This capacitor is 80μF (and discharging) instead of 22. The soldering was not quite good, i'm cleaning the PCB now and i'll let you know

It can't be such a big damage while i was playing with the meter, very strange
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Old 26th September 2012, 11:07 PM   #20
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Actually i found the problem...
When i first smelled some burn it was close to the volume knob area.
After taking some closer look i noticed this:

Click the image to open in full size.

I just touched the route (sorry for not knowing the word) and simply came off the pcb, it had also some small burn sign.

Now what?

I studied electrical engineer but don't know a thing of printing circuit boards ,lol
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