Searching \ for '[EE] How to do this board rework?' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: massmind.org/techref/index.htm?key=how+board+rework
Search entire site for: 'How to do this board rework?'.

Exact match. Not showing close matches.
PICList Thread
'[EE] How to do this board rework?'
2009\04\27@012909 by Bob Blick

face
flavicon
face
part 0 44 bytes
his is a multi-part message in MIME format.
part 1 1538 bytes content-type:text/plain; charset=ISO-8859-1 (decoded 7bit)

I have a Rockford Fosgate amplifier, about 8 years old, and one channel
died and I need to replace two TO-220 transistors. The transistors are
not bolted directly to the heatsink, they are soldered to an
intermediate PC board that has an aluminum core. If you're familiar with
heatsinked LEDs you are probably familiar with aluminum core PC board.

I'm looking for advice about how to change these transistors. The amp
will cost about $300-$400 for a new one, plus a new model will need to
be fitted to my car which is a hassle working upside down in the trunk,
so I'm willing to invest a couple of hours fixing this one.

Unsoldering and then soldering in two new parts without making a mess
out of it or ruining the adjacent transistors is something I'm afraid
of, getting enough heat to the area will require pulling the main board
and the two transistor boards(there's a mirror-image board on the other
edge of the amp) and probably desoldering all the transistors from the
main board so I can concentrate on just the transistor board which has a
dozen transistors on it.

I'm tempted to cut out an area of the PC board with those two
transistors and drill and tap the heatsink directly and use normal mica
insulators to mount the new parts. But that is pretty brute force and
stupid although it would probably work.

Anyone fixed anything like this before? Heat gun? Oven? Bacon Lance?
I've attached a picture of part of the amp showing some of the
transistor board and main board.

Thanks,

Bob



part 2 30655 bytes content-type:image/jpeg; (decode)


part 3 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2009\04\27@014300 by Xiaofan Chen

face picon face
On Mon, Apr 27, 2009 at 1:29 PM, Bob Blick <spam_OUTbobblickTakeThisOuTspamftml.net> wrote:
> Anyone fixed anything like this before? Heat gun? Oven? Bacon Lance?
> I've attached a picture of part of the amp showing some of the
> transistor board and main board.
>

If you have extra TO-220 transistors for your board, the easiest way is
to cut three legs and then take it out. ;-)

--
Xiaofan http://mcuee.blogspot.com

2009\04\27@014717 by AGSCalabrese

picon face
Cut the leads at the transistor body.
Grind the transistor body away.
Solder the new transistor to the existing leads and to the
metal tab that remains of the former transistor.
Gus


{Quote hidden}

2009\04\27@015803 by Ruben Jönsson

flavicon
face
If you have the room on the height you can perhaps keep the bad transistors
there. You have to put a metal bar on top of the old tranaistors metal tab and
screw the new one on to that. Cut the legs of the old transistor and remove
them so you can solder the new on the board or you can just solder the new on
the old ones (still cutting them of course). Perhaps you have to make a special
metal bar by machining it to cover the whole metal tab of the new transistor.
By making the metal bar long enough for both transistors they will share the
same thermal environment (which I think is important here).

Just a thought.

/Ruben


{Quote hidden}

==============================
Ruben Jönsson
AB Liros Electronic
Box 9124, 200 39 Malmö, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
.....rubenKILLspamspam@spam@pp.sbbs.se
==============================

2009\04\27@020433 by cdb

flavicon
face
We used to use the paint stripper or hair dryer for removing
components from base station filter amplifiers.

Foil around or over devices we didn't want too damaged by heat and
then away we went.

Colin
--
cdb, colinspamKILLspambtech-online.co.uk on 27/04/2009

Web presence: http://www.btech-online.co.uk  

Hosted by:  http://www.1and1.co.uk/?k_id=7988359







2009\04\27@022041 by Tony Smith

flavicon
face
> I have a Rockford Fosgate amplifier, about 8 years old, and one channel
died and I
> need to replace two TO-220 transistors. The transistors are not bolted
directly to the
> heatsink, they are soldered to an intermediate PC board that has an
aluminum core. If
> you're familiar with heatsinked LEDs you are probably familiar with
aluminum core PC
> board.
>
> I'm looking for advice about how to change these transistors. The amp will
cost about
> $300-$400 for a new one, plus a new model will need to be fitted to my car
which is a
> hassle working upside down in the trunk, so I'm willing to invest a couple
of hours fixing
> this one.


I did something like this a few months back, it was a motor control.  You
need to get a lot of heat into a small area as fast as possible.  No
worries!

I clipped the leads near the transistor body, and bent them straight.  I
don't have a hot-air rework station, but I do have a 2000W heat gun.
Nothing special, but I've made some attachments to reduce the ~30mm output
to something smaller (about 3 - 15mm).  The fan needed to be upgraded, of
course.

Grab the transistor with pliers, and hit the metal tab with the heat gun.
It should come off after a few seconds.  The leads you can get out with a
normal soldering iron.  Using the heat gun might fry the board.

Tony

2009\04\27@041829 by Mike Harrison

flavicon
face
On Sun, 26 Apr 2009 22:29:12 -0700, you wrote:

{Quote hidden}

Metcal iron with STTC117 or 817 bit should do it - this can pump a ton of heat in quickly without
overshoot.  


2009\04\27@081751 by John Ferrell

face
flavicon
face
Just what is a "Bacon Lance"?

>
> Anyone fixed anything like this before? Heat gun? Oven? Bacon Lance?
> I've attached a picture of part of the amp showing some of the
> transistor board and main board.
>
> Thanks,
>
> Bob
>
>


--------------------------------------------------------------------------------


> --

2009\04\27@123406 by Bob Blick

face
flavicon
face
www.popsci.com/bacon

John Ferrell wrote:
> Just what is a "Bacon Lance"?
>
>> Anyone fixed anything like this before? Heat gun? Oven? Bacon Lance?
>> I've attached a picture of part of the amp showing some of the
>> transistor board and main board.

2009\04\27@171434 by John Ferrell

face
flavicon
face
Got me! I thought it was something other than humor....

----- Original Message -----
From: "Bob Blick" <.....bobblickKILLspamspam.....ftml.net>
To: "Microcontroller discussion list - Public." <EraseMEpiclistspam_OUTspamTakeThisOuTmit.edu>
Sent: Monday, April 27, 2009 12:33 PM
Subject: Re: [EE] How to do this board rework?


> http://www.popsci.com/bacon
>
> John Ferrell wrote:
>> Just what is a "Bacon Lance"?
>>
>>> Anyone fixed anything like this before? Heat gun? Oven? Bacon Lance?
>>> I've attached a picture of part of the amp showing some of the
>>> transistor board and main board.
> --

2009\04\28@154725 by Clint Sharp

picon face
In message <49F542A8.8030908spamspam_OUTftml.net>, Bob Blick <@spam@bobblickKILLspamspamftml.net>
writes
>I have a Rockford Fosgate amplifier, about 8 years old, and one channel
>died and I need to replace two TO-220 transistors. The transistors are
>not bolted directly to the heatsink, they are soldered to an
>intermediate PC board that has an aluminum core. If you're familiar with
>heatsinked LEDs you are probably familiar with aluminum core PC board.
Seen that sort of thing before in laptops and on the 'star' type LEDs as
well as a NiCd battery matching/conditioning system for RC racing packs.
>Anyone fixed anything like this before? Heat gun? Oven? Bacon Lance?
Hotplate and soldering iron (actually a pair of Weller W60 irons with
two pairs of hands) worked for us but ymmv.

I don't know the configuration of the amp but you may find that doing a
little matching of devices will pay dividends, if the transistors on the
board are cheap or are part of the same circuit 'block' then I'd replace
the lot in one go instead of trying to fix only the faulty bits on the
channel just to save the effort of having to do it all again.

Of course, if I'm trying to teach granny to suck eggs then please ignore
me.

(BTW, I built the car computer SMPSU on your site, works very well,
thanks)

{Quote hidden}

--
Clint Sharp


'[EE] How to do this board rework?'
2009\05\03@220002 by Bob Blick
face
flavicon
face
part 0 44 bytes
his is a multi-part message in MIME format.
part 1 1054 bytes content-type:text/plain; charset=windows-1250 (decoded 7bit)

I took all your advice and fixed my amplifier using what I could lay my
hands on.

BUZ21 and BUZ272 transistors were not readily available, I used IRF540
and IRF9540. I found a schematic online for a similar Rockford Fosgate
amp so I was able to see what else was likely to be bad, but as it turns
out just those two transistors were bad. They weren't part of any
parallel group, it's a smallish 4-channel amp (200a4, 4x50 watt).

I tinned the backside of the new parts and used a heat gun(paint
stripping type) on "low" to heat the bottom side of the aluminum PC
board, and used my 260 watt soldering gun on the tab.

One transistor flowed in nicely, the other not so nicely. But good
enough. The quiescent current was very close and trimmed right in, the
amp works fine again. I have no idea why it failed. The speakers are not
shorted, when it died I was just listening to talk radio, and it wasn't
hot when it died.

Thanks again for all your help. Attached is a photo of the repaired area.

Cheers,
Bob


part 2 29574 bytes content-type:image/jpeg; (decode)


part 3 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

More... (looser matching)
- Last day of these posts
- In 2009 , 2010 only
- Today
- New search...