As I said: you have to check one thing at a time and in isolation of its neighbours. Laborious but essential if you don't want the neighbouring connected components to mislead you.
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As I said: you have to check one thing at a time and in isolation of its neighbours. Laborious but essential if you don't want the neighbouring connected components to mislead you.
Phil that bridge rectifier is very similar to the one I used to fix one of of my 211 monoblocks a few months ago and documented on this forum.
I kinda feel your point that what's causing this issue is something that is failing when power is applied but looks fine when tested with power off.
You might not know I replaced all the output transistors and used what seemed to be incredibly expensive thermal paste. I went for the best stuff I could find, though.
Justin, I've only been on this forum 2 or 3 weeks and so far have only looked at 2 or 3 threads that caught my interest. If you are aware that they're available that's great.Quote:
Originally Posted by User211
Since everything seems to test OK when tested in isolation, it's what I'm leaning towards. It's what I would be looking at.Quote:
Originally Posted by User211
Ah, didn't know that, or it hadn't filtered through to my brain. What colour was the thermal paste? If it's grey or silver in colour, then it's likely to be silver loaded. It will be more expensive than the white aluminium oxide paste, simply because it has silver in it. It's generally more readily available because it's used by computer builders and there are a lot of them still about. It is preferred by them because it has better thermal conductivity, which if you're trying to prevent a CPU going into, in some cases a literal meltdown, it matters. The down side is, it's also electrically conductive (aluminium oxide is an insulator), which is why the instructions typically tell you not to apply too much, and if you do, to make sure you clean the excess off the board.Quote:
Originally Posted by User211
I don't know what you used, but it may be something to think about.
Phil
CHIP-QUIK TC3 was the paste.
https://sansui-vintage.com/product/r...00-ba3000-nos/ also has SG-5TR.
Not cheap, but hey, be nice to use the original parts.
I wish I had a variac. That way I could verify that the diode network works until a given voltage point. We know they are good for 500mV but that's sod all.
It's tempting to go for it and just order the diodes and plumb them in since they are both isolated now.
The new transistors went in post amp being busted. When doing my testing and comparing across monoblocks, neither amp has the driver or protection boards installed. So that scope rules out the transistors.
I looked up the specs of the chip quik, it says it's insulating so I guess that theory can be ruled out. It was worth finding that out though, one less thing to worry about.
I presume you are aware that the SG-5TR and SG-5TS are different, one is common cathode and the other is common anode, so you can't replace one with the other. I don't know which is which because I can't find a data sheet for either of them and I can't work it out from the pictures because I don't know which wire is the positive rail and which is the negative.
A variac would be handy but not just for the reason you're thinking of, it will reduce the amount of stress the components are put under during fault conditions like you have here. The 500mV sounds like it might be the forward voltage drop of the diodes when they are conducting. It seems a bit low but if the diodes are passing considerable current, which I guess they are, they will be heating up quite a bit, so that could explain it.
If it were me, I would buy that bridge rectifier and fit it temporarily. If it makes no difference, then the problem doesn't lie with the original rectifiers, it's somewhere else further along. If it does make a difference, then there is an issue with the rectifiers (or their mounting) that needs further investigation. It's a process of dealing with the possibilities one at a time and working through step by step.
As far as originality goes, I'm a bit ambivalent about it. Personally speaking, I think there are places where it matters and places where it doesn't, or perhaps I should say, isn't detrimental. Other people will have different opinions on this, but there are certainly situations where components, that were originally fitted, were only just up to the job, but they were the best that was available at the time. In this case replacing them with something newer may be a good move for reliability reasons and availability may force your hand anyway.
Taking an example from the classic car world, I periodically do work on Aston Martins, and a surprising number of early, high value ones (DB4,5 and 6s) are fitted with electronic ignition and in some cases, also well disguised electronic fuel injection. These are prize winning concours cars, where originality matters, but these modifications mean the cars can stay on the road and be used and enjoyed, rather than being a 4 wheel doorstop. I suppose it all depends on your priorities.
I also know owners that never drive them, and are quite happy to sit and look at them and polish them periodically. I don't get it, but it's their car and their call, I think they're missing the point of ownership, but that's just my opinion. There is one owner who has this approach that I can relate too. He's registered blind and consequently doesn't have a driving license. He bought his as a barn find and restored it, and (with the help of one of his children) has restored it to show worthy condition and by all accounts has done a very good job.
The 500mV is just the test voltage applied by my multimeter I think.
Re NOS parts I'd rather use them. Swapping all the power transistors for modern equivalents as I have done may well sound odd as they won't perform the same as the original parts, even though on paper they are better. It's a calculated risk I have taken. If they sound shite I will be forced to get some NOS ones. They are available.
I might get a variac - looks like £140 does it. For the moment I just need to get that tranny back in - waiting for some wire cutters to arrive as the ones I have aren't up to it. The tranny is unbelievably heavy. It can never have been cheap to make.
Thanks for your advice it is carefully being considered.
Justin do you want to borrow my variac? It isn't getting any use atm.
I will be coming down the M5 in a week to 10 days, depending when this gas bubble in my eye eventually is absorbed.
I can swing by on my way down to south Wales.
Alan just let me know when you will be coming. I dunno if you are up for a debug session when you arrive but that would be cool. With both monos disassembled to a greater or lesser extent a perusal by yourself would probably be invaluable.
I plan to plumb the transformer back in but leave the two 64.5V windings open and check them first. Then wire them back in and check that dual diode snubbered rectifier setup yet again now I understand it better if the transformer really is OK.
It probably is best I buy a variac though.
I just want to get to a state where I can maintain what I own.
Thanks for the offer. Might be well worth bringing it.
I've taken about 70% of this circuit out of the equation and I still can't debug it.
I am doing the equivalent of software unit, integration and system tests on the 30% I have isolated the fault to and I am still clueless.
Amazed.
And totally intrigued.https://uploads.tapatalk-cdn.com/202...e606649e80.jpg
Extracted transformer and diode network re-instated. Hence all the blue heat shrink on the right hand side.
Loads of flux mess and solder splutter to clean up but I am sure that's wired correctly.
See a flaw in that anyone and please tell me. It's an amateur job but I am sure all those connections are sound.
Bridge rectifier also re-instated but no heat shrink as per the original set up.
I wonder if anyone from Accuphase has picked up on this thread. If so, send your best engineer to my address by first class air ticket immediately:) LOL.https://uploads.tapatalk-cdn.com/202...648d700f8b.jpg