Help sorrow!
My Kenwood/ Trio mono block just died.
I never smelled anything or heard any untoward noise but when I noticed my subwoofer wasn't working.
I just pulled the covers off the amp and I have found a big ( 1cm ) hole in the circuit board, but no apparent exploded components, does look overheated tho
Is there any-one here with experience in the old classic trios??
Is it worth trying to find a replacement board or is it possible to have a new one made??
Any Aussies living in Geelong or close by able to help??
My Kenwood/ Trio mono block just died.
I never smelled anything or heard any untoward noise but when I noticed my subwoofer wasn't working.
I just pulled the covers off the amp and I have found a big ( 1cm ) hole in the circuit board, but no apparent exploded components, does look overheated tho
Is there any-one here with experience in the old classic trios??
Is it worth trying to find a replacement board or is it possible to have a new one made??
Any Aussies living in Geelong or close by able to help??
Picture of hole
It's big, 1.5cm across, must have got very hot.
http://farm3.static.flickr.com/2443/3610405812_d2734d02fb.jpg?v=0
It's big, 1.5cm across, must have got very hot.
http://farm3.static.flickr.com/2443/3610405812_d2734d02fb.jpg?v=0
Moondog55 said:
Finding a new board is extremely unlikely. The damage in any case seems easily repairable. But is this the reason the amp is not working? I find it very strange that anything can burn through the board without leaving smell, fireworks or pieces of dead components behind. Can you do basic troubleshooting? Is the damage in the PS area? Maybe a power surge caused the loss of incoming AC power. It may turn out to be trivial to repair.
While able to work cross-overs and build speakers I find myself totally out of my depth with electronics.
I'm without even those basic troubleshooting skills.
Learning electronics and how to build and repair amplifiers was going to be my next 10 year plan.
I made the mistake of leaving the system switched on overnite, but the smell of burnt Bakelite lingers in the casing but no, I found nothing inside but a greasy residue, soot I suppose, inside the case
I'm without even those basic troubleshooting skills.
Learning electronics and how to build and repair amplifiers was going to be my next 10 year plan.
I made the mistake of leaving the system switched on overnite, but the smell of burnt Bakelite lingers in the casing but no, I found nothing inside but a greasy residue, soot I suppose, inside the case
Well, I hang out here too. 
But why you think I've got a rabbit to pull out of my hat is a mystery.
Anyway, here's the section of the board that is toasted according to your pic (circled in red):
IF that hole is new, and the main symptom of the current failure, I'd venture to say that the amp oscillated itself to death and these resistors (and perhaps the .047µf film cap) experienced a total meltdown...although why it didn't set off smoke detectors in the house is a mystery. Can't say that I see holes in PC boards too often.
Here's a thread over at AK about the oscillation problems in the L-07MII amp, which I believe is due to a combination of aging electrolytic caps, and especially due to the use of what I call 'Black Flag' ceramic caps used for the 'pf'-values on the driver board. I've seen these 'Black Flag' caps on several high-speed amps (Kenwood L-07MII, Sansui AU-919 & BA-F1, and a few others), and I believe they are an early design of a stacked ceramic cap that simply goes bad over the years.
Something else you may have to fight is that many of these amps sold in countries other than the US had a thermal fuse installed inside the transformer housing. When the amp self-destructs like this, the thermal fuse often dies too as the transformer overheats. I have had zero luck trying to replace this fuse on my own, but instead have sent the transformer off to a pro and let him deal with it.
The last bummer is that you may have killed the super-rare Panasonic output transistors (2SC2337A and 2SA1007A). These are what give the amp its speed and rather nice sound. The best you can probably do (if you find dead ones) is to replace them all with 2SA1116 and 2SC2607 from this guy here, who has a small supply of these original transistors which are not as fast as the originals, but make a good replacement nonetheless.
But why you think I've got a rabbit to pull out of my hat is a mystery.
Anyway, here's the section of the board that is toasted according to your pic (circled in red):
An externally hosted image should be here but it was not working when we last tested it.
IF that hole is new, and the main symptom of the current failure, I'd venture to say that the amp oscillated itself to death and these resistors (and perhaps the .047µf film cap) experienced a total meltdown...although why it didn't set off smoke detectors in the house is a mystery. Can't say that I see holes in PC boards too often.
Here's a thread over at AK about the oscillation problems in the L-07MII amp, which I believe is due to a combination of aging electrolytic caps, and especially due to the use of what I call 'Black Flag' ceramic caps used for the 'pf'-values on the driver board. I've seen these 'Black Flag' caps on several high-speed amps (Kenwood L-07MII, Sansui AU-919 & BA-F1, and a few others), and I believe they are an early design of a stacked ceramic cap that simply goes bad over the years.
Something else you may have to fight is that many of these amps sold in countries other than the US had a thermal fuse installed inside the transformer housing. When the amp self-destructs like this, the thermal fuse often dies too as the transformer overheats. I have had zero luck trying to replace this fuse on my own, but instead have sent the transformer off to a pro and let him deal with it.
The last bummer is that you may have killed the super-rare Panasonic output transistors (2SC2337A and 2SA1007A). These are what give the amp its speed and rather nice sound. The best you can probably do (if you find dead ones) is to replace them all with 2SA1116 and 2SC2607 from this guy here, who has a small supply of these original transistors which are not as fast as the originals, but make a good replacement nonetheless.
Hi Echowars,
I knew you were here too...
I had already searched quickly on AK and saw a comment by you on this amp, saying that the 'II' was prone to oscillation but the 'I' wasn't. So I thought you were the man with the rabbit!
Plus you've helped me over at AK with one of my old Japanese classics...
You da man!
Cheers
Stuey
I knew you were here too...
I had already searched quickly on AK and saw a comment by you on this amp, saying that the 'II' was prone to oscillation but the 'I' wasn't. So I thought you were the man with the rabbit!
Plus you've helped me over at AK with one of my old Japanese classics...
You da man!
Cheers
Stuey
Oops....yes, those are NEC trannies, not Panasonic.Moondog55 said:
To protect the amp, the pf-value caps (the 'Black Flag' caps) need to be replaced. I replace them with silver mica's. It's also a great idea to get rid of the original electrolytic caps, as their age may well contribute to the failure. I also usually replace Cf9 with a good metalized polypropylene (or metal polyester) cap.
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