Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default LM7815A and LM7915A metal tab or no metal tab?

I'm servicing a Behringer EUROPOWER PMH2000. The + and - 15 volt regulators
need replacing because the leads have failed. The transistor is mounted to
the chassis at a 90 degree angle and then soldered to the pc board. The
problem is that pc board fits very tightly into the chassis. The leads on
the regulators keep getting flexed with each pc board removal. Anyway, I
want to replace them because a couple of the leads have broken off. They are
packaged in a TO-220 case. The center tab is nonmetallic so it is insulated
from the chassis. Though the schematic says terminal 2 is grounded in the
7815A anyway, I was wondering if it made any difference whether or not I
purchased ones with metallic backing or ones with a plastic backing.

I just looked at the LM7915 spec sheet and it says that terminal 1 is ground
and terminal 2 is the input which is reversed from the positive regulator.
It also doesn't mention whether or not it has a metal tab, which if it did,
would have to be insulated from the chassis. Do any of you have any
experience replacing these regulators in a chassis mount situation?

Thanks for your reply.
--
David Farber
Los Osos, CA


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Default LM7815A and LM7915A metal tab or no metal tab?

On Tuesday, December 26, 2017 at 2:16:52 PM UTC-8, David Farber wrote:
I'm servicing a Behringer EUROPOWER PMH2000. The + and - 15 volt regulators
need replacing because the leads have failed. The transistor is mounted to
the chassis at a 90 degree angle and then soldered to the pc board. The
problem is that pc board fits very tightly into the chassis. The leads on
the regulators keep getting flexed with each pc board removal. Anyway, I
want to replace them because a couple of the leads have broken off. They are
packaged in a TO-220 case. The center tab is nonmetallic so it is insulated
from the chassis.


I presume, however, that the tab connects to the chassis for heatsinking?

Best practice if the strain on the component is breaking wires, is to use
a strain-relieved wiring connection, like a few-inches pigtail wiring from the
regulator to a female Molex KK socket; this will plug onto male pins mounted
in the printed wiring board, 0.100" centers spacing just like the LM78xx.

Those regulators are available in fullpak (epoxy insulated tab), metal-tab-wth-hole,
and short-metal-tab (for soldering to a surface mount "heatsink").
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Default LM7815A and LM7915A metal tab or no metal tab?

David Farber wrote:

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

I'm servicing a Behringer EUROPOWER PMH2000. The + and - 15 volt regulators
need replacing because the leads have failed. The transistor is mounted to
the chassis at a 90 degree angle and then soldered to the pc board. The
problem is that pc board fits very tightly into the chassis. The leads on
the regulators keep getting flexed with each pc board removal. Anyway, I
want to replace them because a couple of the leads have broken off. They are
packaged in a TO-220 case. The center tab is nonmetallic so it is insulated
from the chassis.


** The *mounting tab* is definitely metal, just coated in epoxy to insulate it.


Though the schematic says terminal 2 is grounded in the
7815A anyway, I was wondering if it made any difference whether or not I
purchased ones with metallic backing or ones with a plastic backing.

I just looked at the LM7915 spec sheet and it says that terminal 1 is ground
and terminal 2 is the input which is reversed from the positive regulator.
It also doesn't mention whether or not it has a metal tab, which if it did,
would have to be insulated from the chassis. Do any of you have any
experience replacing these regulators in a chassis mount situation?


** If the originals are held on with a clamp, you need to buy the same again.

If held with 3mm bolts, you can use the ones you have.

BUT you MUST add insulating bushes and mica pads to BOTH - plus a smear of white thermal grease.

Bolting the positive one straight to the chassis is likely to result in ground loop hum.


.... Phil
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Default LM7815A and LM7915A metal tab or no metal tab?

whit3rd wrote:
On Tuesday, December 26, 2017 at 2:16:52 PM UTC-8, David Farber wrote:
I'm servicing a Behringer EUROPOWER PMH2000. The + and - 15 volt
regulators need replacing because the leads have failed. The
transistor is mounted to the chassis at a 90 degree angle and then
soldered to the pc board. The problem is that pc board fits very
tightly into the chassis. The leads on the regulators keep getting
flexed with each pc board removal. Anyway, I want to replace them
because a couple of the leads have broken off. They are packaged in
a TO-220 case. The center tab is nonmetallic so it is insulated from
the chassis.


I presume, however, that the tab connects to the chassis for
heatsinking?

Best practice if the strain on the component is breaking wires, is to
use
a strain-relieved wiring connection, like a few-inches pigtail wiring
from the regulator to a female Molex KK socket; this will plug onto
male pins mounted
in the printed wiring board, 0.100" centers spacing just like the
LM78xx.

Those regulators are available in fullpak (epoxy insulated tab),
metal-tab-wth-hole, and short-metal-tab (for soldering to a surface
mount "heatsink").


Yes, the tab is for heat sinking and your suggestion of using the Molex plug
and socket is very clever.

Thanks for your reply.
--
David Farber
Los Osos, CA


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Default LM7815A and LM7915A metal tab or no metal tab?

Phil Allison wrote:
David Farber wrote:

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

I'm servicing a Behringer EUROPOWER PMH2000. The + and - 15 volt
regulators need replacing because the leads have failed. The
transistor is mounted to the chassis at a 90 degree angle and then
soldered to the pc board. The problem is that pc board fits very
tightly into the chassis. The leads on the regulators keep getting
flexed with each pc board removal. Anyway, I want to replace them
because a couple of the leads have broken off. They are packaged in
a TO-220 case. The center tab is nonmetallic so it is insulated from
the chassis.


** The *mounting tab* is definitely metal, just coated in epoxy to
insulate it.


Though the schematic says terminal 2 is grounded in the
7815A anyway, I was wondering if it made any difference whether or
not I purchased ones with metallic backing or ones with a plastic
backing.

I just looked at the LM7915 spec sheet and it says that terminal 1
is ground and terminal 2 is the input which is reversed from the
positive regulator. It also doesn't mention whether or not it has a
metal tab, which if it did, would have to be insulated from the
chassis. Do any of you have any experience replacing these
regulators in a chassis mount situation?


** If the originals are held on with a clamp, you need to buy the
same again.

If held with 3mm bolts, you can use the ones you have.

BUT you MUST add insulating bushes and mica pads to BOTH - plus a
smear of white thermal grease.

Bolting the positive one straight to the chassis is likely to result
in ground loop hum.


... Phil


Hi Phil,

The original ones do not have any insulating bushings or mica pads. They are
mounted to the chassis with 3mm bolts and some thermal grease. I contacted
Digi-Key but they could not tell me if their parts were insulated or not.
When I place my order, I will get the insulating pads and bushings just to
make sure.

By the way, you can get a schematic here.
http://music-electronics-forum.com/a...h2000_-et-.zip

Thanks for your reply.
--
David Farber
Los Osos, CA





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Default LM7815A and LM7915A metal tab or no metal tab?

On 2017/12/27 12:31 PM, David Farber wrote:
whit3rd wrote:
On Tuesday, December 26, 2017 at 2:16:52 PM UTC-8, David Farber wrote:
I'm servicing a Behringer EUROPOWER PMH2000. The + and - 15 volt
regulators need replacing because the leads have failed. The
transistor is mounted to the chassis at a 90 degree angle and then
soldered to the pc board. The problem is that pc board fits very
tightly into the chassis. The leads on the regulators keep getting
flexed with each pc board removal. Anyway, I want to replace them
because a couple of the leads have broken off. They are packaged in
a TO-220 case. The center tab is nonmetallic so it is insulated from
the chassis.


I presume, however, that the tab connects to the chassis for
heatsinking?

Best practice if the strain on the component is breaking wires, is to
use
a strain-relieved wiring connection, like a few-inches pigtail wiring
from the regulator to a female Molex KK socket; this will plug onto
male pins mounted
in the printed wiring board, 0.100" centers spacing just like the
LM78xx.

Those regulators are available in fullpak (epoxy insulated tab),
metal-tab-wth-hole, and short-metal-tab (for soldering to a surface
mount "heatsink").


Yes, the tab is for heat sinking and your suggestion of using the Molex plug
and socket is very clever.

Thanks for your reply.


I would not agree with using a socket if the regulator flexes slightly.
You will run through the insertion limit number of the socket very
quickly. Rather, can you solder a flexible loop to the regulator leads -
assuming the PCB and the heat sink are not well joined so there is some
flex.

I have seen sockets used in similar situations in arcade games and the
failure rate is significant. Connectors are the principle point of
failure after all...

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
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Default LM7815A and LM7915A metal tab or no metal tab?

On Wednesday, December 27, 2017 at 2:43:04 AM UTC-5, Phil Allison wrote:
David Farber wrote:

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

I'm servicing a Behringer EUROPOWER PMH2000. The + and - 15 volt regulators
need replacing because the leads have failed. The transistor is mounted to
the chassis at a 90 degree angle and then soldered to the pc board. The
problem is that pc board fits very tightly into the chassis. The leads on
the regulators keep getting flexed with each pc board removal. Anyway, I
want to replace them because a couple of the leads have broken off. They are
packaged in a TO-220 case. The center tab is nonmetallic so it is insulated
from the chassis.


** The *mounting tab* is definitely metal, just coated in epoxy to insulate it.

Huh, we buy either spendy teflon shoulder washers, or cheaper nylon.
(with 4-40 screw.)

George H.


Though the schematic says terminal 2 is grounded in the
7815A anyway, I was wondering if it made any difference whether or not I
purchased ones with metallic backing or ones with a plastic backing.

I just looked at the LM7915 spec sheet and it says that terminal 1 is ground
and terminal 2 is the input which is reversed from the positive regulator.
It also doesn't mention whether or not it has a metal tab, which if it did,
would have to be insulated from the chassis. Do any of you have any
experience replacing these regulators in a chassis mount situation?


** If the originals are held on with a clamp, you need to buy the same again.

If held with 3mm bolts, you can use the ones you have.

BUT you MUST add insulating bushes and mica pads to BOTH - plus a smear of white thermal grease.

Bolting the positive one straight to the chassis is likely to result in ground loop hum.


... Phil


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Default LM7815A and LM7915A metal tab or no metal tab?

wrote:

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



** The *mounting tab* is definitely metal, just coated in epoxy to
insulate it.



Huh, we buy either spendy teflon shoulder washers, or cheaper nylon.
(with 4-40 screw.)



** JRC make "full pack" versions of the popular 7815/7915, TO220 regs.

Types are JRC7815A and JRC7915A.

https://img.alicdn.com/imgextra/i3/T...0-item_pic.jpg


The pak is called a T220F

Lots of ICs are made like this, with a penalty in the thermal resistance spec.


...... Phil

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Default LM7815A and LM7915A metal tab or no metal tab?

Phil Allison wrote:
wrote:

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



** The *mounting tab* is definitely metal, just coated in epoxy to
insulate it.



Huh, we buy either spendy teflon shoulder washers, or cheaper nylon.
(with 4-40 screw.)



** JRC make "full pack" versions of the popular 7815/7915, TO220 regs.

Types are JRC7815A and JRC7915A.

https://img.alicdn.com/imgextra/i3/T...0-item_pic.jpg


The pak is called a T220F

Lots of ICs are made like this, with a penalty in the thermal
resistance spec.


..... Phil


I meant to post the following to the group yesterday
---------------------------------------------------------------------

First, thanks for posting that pic.

I finally found out what was causing the roadblock in my search for the
LM7815/7915 in the epoxy case. STMIcroelectronics makes this part and it is
available at both Mouser and Digi-Key. The difference lies in the part
number for the epoxy case. The letter "M" is dropped from the part number.
They are L7815CP and L7915CP. Of course those numbers don't turn up when you
look for the original part number.

That being said, I think you were implying it's still better to use the
metal tabbed package and use insulating hardware which will improve the
thermal transfer. Is that correct?

Thanks for your reply.

--
David Farber
Los Osos, CA




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Default LM7815A and LM7915A metal tab or no metal tab?

On 12/29/17 10:39 AM, David Farber wrote:
That being said, I think you were implying it's still better to use the
metal tabbed package and use insulating hardware which will improve the
thermal transfer. Is that correct?


Just a wild guess here...
But I suspect the epoxy coating may have less thermal resistance
than a mica washer with the bare metal tab.

--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com
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Default LM7815A and LM7915A metal tab or no metal tab?

Fox's Mercantile wrote:
On 12/29/17 10:39 AM, David Farber wrote:
That being said, I think you were implying it's still better to use
the metal tabbed package and use insulating hardware which will
improve the thermal transfer. Is that correct?


Just a wild guess here...
But I suspect the epoxy coating may have less thermal resistance
than a mica washer with the bare metal tab.


I suspect the difference will have minimal effect on the operation of the
mixer. I'll opt for the epoxy coated device.

Thanks for your reply.
--
David Farber
Los Osos, CA


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Default LM7815A and LM7915A metal tab or no metal tab?

On Friday, December 29, 2017 at 12:02:38 PM UTC-5, Fox's Mercantile wrote:
On 12/29/17 10:39 AM, David Farber wrote:
That being said, I think you were implying it's still better to use the
metal tabbed package and use insulating hardware which will improve the
thermal transfer. Is that correct?


Just a wild guess here...
But I suspect the epoxy coating may have less thermal resistance
than a mica washer with the bare metal tab.

--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com




Fullpack transistors generally have a much lower wattage rating than their metal backed counterparts for that very reason.

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