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Old 10th July 2012, 12:21 PM   #21
Simon B is offline Simon B  United Kingdom
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Quote:
Originally Posted by Enzo View Post
.... I am not aware of any goo-only insulators.....
Me neither, and I wouldn't trust it if there were one.

You could try lifting the mica wafer (thin ones aren't always that visible at first) by carefully sliding the tip of a scalpel under one corner. If you can get it off in one piece (mica is brittle), do so.

Clean off all the old heatsinking compound carefully, and de-burr the mounting hole on the new chip with a countersinking bit.

When re-assembling, spread fresh heatsinking compound thinly, mate the surfaces lightly then see where the hills and valleys are and smooth them out.

An added finned heatsink, on whichever side you can most easily mount it as a very good idea, that bit of aluminium they've stuck it on is laughably poor.

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Old 10th July 2012, 12:35 PM   #22
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I just checked it the same way as if it were off the board. It gives me some strange readings, so I'd like to replace it, but it seems to be hard to find.
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Old 10th July 2012, 03:28 PM   #23
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Originally Posted by Simon B View Post
Me neither, and I wouldn't trust it if there were one.
That makes three of us

As you say, sometimes mica washers are hard to see.
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Old 10th July 2012, 04:44 PM   #24
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I meant the KBU1003G seems hard to find unless I want to buy 500 of them.
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Old 10th July 2012, 11:30 PM   #25
Enzo is offline Enzo  United States
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It is just a 10 amp 200 volt bridge, nothing special. You don't need to get that exact part numner. ANy similar brand will do. And if you have a 400 volt version or something, that will be fine also. The AVT50 is only rectifying 25VAC x 2.

Go to Mouser and search "10A bridge." They have several selections. Here is one, BR102 for $1.13 each:
http://www.rectron.com/data_sheets/br1005-1010.pdf

And they don;t stock the KBU1003, but they do stock the KBU1004, which is just the 400v version instead of the 200v version:
http://www.taiwansemi.com/db/picture...01/KBU1001.pdf

SInce the KBU one is upright and inline, while the BR is mounted flat and is square, I;'d go with the KBU, since that is what your board is laid out for.

And if you are somewhere that Mouser doesn't serve, just find any 10A bridge in the shape you like with 200v or higher rating.
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Old 11th July 2012, 12:01 AM   #26
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Thanks a ton. I called a few suppliers, and they said there was no substitution available for that rectifier, so that's a relief.

Do I have to worry about the pinouts, or are they all the same order?

I'd guess that the KBU1004 would be identical because the datasheet lists the whole family together on one posting.
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Old 11th July 2012, 08:02 AM   #27
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Originally Posted by j4976 View Post
Thanks a ton. I called a few suppliers, and they said there was no substitution available for that rectifier, so that's a relief.

Do I have to worry about the pinouts, or are they all the same order?
There are various different pin layouts, you need to check the actual PCB to ensure you connect it correctly - or simply fit four separate rectifiers to make the bridge (I've often done that over the years).
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Old 11th July 2012, 08:46 AM   #28
Enzo is offline Enzo  United States
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Pinouts can vary, but if you replace a KBU1003 with a KBU1004, I am willing to wager they will be the same. The square ones tend to be alike: AC on opposite corners, DC on remaining opposite corners. The inlines can have AC in the middle or AC on the ends. And probably the other combinations at some point.

It pays to know the parts and look for equivalents. If that part is obsoleted, then sales are limited to however many they have left. COuld be six of them, sould be six hundred thousand of them. But once obsoleted, many suppliers will erase it from the catalog. SO if you ask for a "replacement" they will look up a cross reference and find nothing. If you ask for a 10A 200v bridge, they will find many. And if you ask for a 10A bridge 200v OR HIGHER, they will find even more.


Many parts that are really generic become hard to find if you look for the exact part. For example some Omron relay might be in something and you want a new one. We may find that Omron does not import that model into the USA, so it is not available here if you look for the exact same part number. But a dozen other identical relays ARE available.
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Old 21st July 2012, 11:08 PM   #29
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Ok. I replaced the rectifier and the 2 large power supply caps. I put everything together, turned all the pots on the front panel to 0, plugged in a speaker, and turned it on. Still have the loud hum. Only left it on for a moment, but the fuse didn't blow.

Any ideas on what to check, so I don't have to check every part on every board?

Thanks.
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Old 23rd July 2012, 06:02 PM   #30
Enzo is offline Enzo  United States
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PLEASE, do not connect speaker to solid state amps until you KNOW they are not producing DC on the output. Loud hum from an amp is almost always either DC on the output or a loss of a main filter. DC on an output will damage the speaker and won;t usually hurt the amp without a load, but with a load, then it has to handle all the failure current.

At this point, most likely problem is a bad power module.
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