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Scary repair - 2285B dual-section caps failed

anderslober said:
CAN you do that? Just 2 15000uf caps...........?
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NO! Your not understanding the power supply and the dual core caps. This is a DUAL power supply (1 for each channel) and you have + and - rails on each channel. Think of the dual core capacitors as TWO individual caps doing supply duty for ONE channel (one cap is doing duty for the + rail and the other for the - rail. One cap of the dual core has it's - terminal to ground supplying a positive voltage and the other cap has it's + terminal to ground supplying a negative voltage.
 
anderslober said:
CAN you do that? Just 2 15000uf caps...........?
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It CAN be done. The problem is you'll have to do a little mod to the power supply by combining the two secondaries in parallel and making it single supply for two amps. I don't recommend doing it unless you know what you're doing. I personally would prefer keeping it separate unless 'I HAVE TO' combine them. <<but that's me.
 
Naaah.....won't be doing that. I would like to keep the unit as stock as possible..........
I'll stuff the cans......IF they need stuffing!

I am travelling at the moment, but when I get back, Ill take a close look at the unit. First thing will to get the fan/softstart running normally again...........
 
ccheath said:
It CAN be done. The problem is you'll have to do a little mod to the power supply by combining the two secondaries in parallel and making it single supply for two amps. I don't recommend doing it unless you know what you're doing. I personally would prefer keeping it separate unless 'I HAVE TO' combine them. <<but that's me.
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I'd never recommend this...any small phase difference will cause huge current spikes in the transformer 60x every second (or 50x in Europe). That, and with dual transformer windings there always seems to be a slight voltage difference, causing more current draw than normal and more transformer heating.

It's just a bad idea all around.
 
ccheath said:
It CAN be done. The problem is you'll have to do a little mod to the power supply by combining the two secondaries in parallel and making it single supply for two amps. I don't recommend doing it unless you know what you're doing. I personally would prefer keeping it separate unless 'I HAVE TO' combine them. <<but that's me.
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Sigh.....

I'm going to have to WATCH you.... :no::no::no::no::no::no::no::no::no::no:
 
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EchoWars said:
I'd never recommend this...any small phase difference will cause huge current spikes in the transformer 60x every second (or 50x in Europe). That, and with dual transformer windings there always seems to be a slight voltage difference, causing more current draw than normal and more transformer heating.

It's just a bad idea all around.
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markthefixer said:
Sigh.....

I'm going to have to WATCH you.... :no::no::no::no::no::no::no::no::no::no:
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I agree with both of you. At least I have said I don't recommend it. I'll keep quiet.
 
MatthewK, thanks for working this one out and putting up all the pictures. This is brilliant, a huge help knowing what to do! (although sorry to revive this one after a couple of months if that's a bad).
 
Matthewk.....others who have done this cap-conversion..........how did you empty the old caps.???????? I have been doing hard labour for more than 3 hours on my dual caps(which were defective)........and I haven't even emptied half of one cap!

What gives? Is there an easier way?
 
I might debate the combined secondary winding issues a little.....

Primary sides are combined all the time.... multi input voltage transformer primaries are in paralleled all the time. A transformer that is designed for 100/120/220/240.... has the two primary 120v windings in parallel for many many years now like 40 years..... series gives you 240v support. They even have multi taps....

There has to be some internal differences in the primary side windings of these multi-voltage transformers....just like you guys are debating on the secondary. There is mutual inductance on the primary side too.....

Don't forget the center tap on the dual transformer is tied to the same ground and to some degree spiking current already... clearly the phasing has to be done correctly. There should be a combined voltage/phase vector component and yes some additional heat.

But I have never tried this on the secondary sides of a dual output transformer and most likely would not.... so don't blame me.... :D
 
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Look at a schematic of a multiple input voltage model that is set up for 120... And you will see parallel windings on the primary side. Yes slightly more heat....

Dual windings on the primary is a no brainer....many folks have the multi voltage units running on 120.

It is possible to parallel windings but some "power derating" would occur. How much I can't state ... And have never done it myself on the secondary side....

As with any design, while there is some down side , there might actually be some upside too... While peak power may be reduced, so may rail sag under peak load may be reduced.

On these transformers, you still only have only one core and input voltage source... Not in a true mono block, like the old 2,5,9,15,16.

I somewhat question the real value of dual secondary windings with a single primary, from what I have seen there tends to be a lot of sag on primary if you don't have a good 120 volt supply. Yes you get some isolation on the secondary side.

So YMMV....



Jk
 
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Can you read a schematic? If not, yes ignore it...and be happy.

Attached is an example of a dual winding on the input side of the transformer. They are configured in parallel for 120 volts and in series for 240.

What I am pointing out is that winding differences of parallel winding have been in our transformers for 40 years or more on the input side...

Question is, how important is it on the output side if you were to parallel a dual output winding.....

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I was quite thrilled by the idea for some weeks having a couple of amps with the same challenge ahead (Sony TA-3650), but today I had some second thoughts.....

By installing the new caps inside the old can you actually created a signicant thermal insulation around the new caps (air). They will heat up more and more when aging and it will be difficult to release their heat. Good you selected 105 degC rated caps, which gives you some larger margin, but still.

I was thinking of putting some heat transfering medium in the void space, like the waxy stuff that was there initially (for the same reason probably); oil will be too difficult and would require safety vent, etc. Question is therefore what kind of stuff would be suitable and available.

Putting in a temperature detector (a regular thermistor) would also be nice to monitor what is actually going on.
 
jstang...I'm just not following you...I think you are referring to something quite different.
I am just in the process of hollowing out the old caps and then put the new caps in the old cans....I just wanted to know if there was an easier way to hollow out the cans......it is NOT easy. This is what my question was pertaining to..........

The heat build up hopefully wont be a problem.............
 
I was commenting on the suggestion below....which in turn was trying to provide you with an option for one set of caps...

Three times removed from the thread starter...... :)


ccheath said:
It CAN be done. The problem is you'll have to do a little mod to the power supply by combining the two secondaries in parallel and making it single supply for two amps. I don't recommend doing it unless you know what you're doing. I personally would prefer keeping it separate unless 'I HAVE TO' combine them. <<but that's me.
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Ok......thanks. I will not be modifying anything to accomodate just 2 caps. I will do the dual cap inside each of the old cans........should be good.
 
wow that is very cool to see the inside of those caps. I went to Brown Institute (Lake Street Murderapolis) after the Army and used to blow up those little capacitors by reverse biasing and turning up the voltage till they exploded leaving bits of paper i the room. Not smart but fun. Ah the fun we had smoking resistors also. I find vintage audio electronics both fascinating and intimidating. Never would think to cut open a cap and put one inside. Very Creative indeed.
 
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