Help identifying a blown transistor

Hi Folks

I have a Commax CDV-43k/DRC-4L (Stock Code: PI-1176) intercom that isn't working anymore. It seems the power supply board in the intercom (CDV-43K) itself (converting wall power of 220v to 15v) has blown. I think it might be the transistor (see photos: https://imgur.com/a/uBCXjwQ). The suppliers say that it is out of warranty and that I would have to buy a new one.

Here is a link with a few photos of a circuit board that isn't working anymore:
https://imgur.com/a/uBCXjwQ

I have tried searching online, but couldn't find anything that gave me any indication of the specs of the transistor or what transistor to try and replace it with. I also tried to search for the schematic, but couldn't find anything.

If anyone can perhaps help me identify the blown transistor or perhaps point me in the right direction that would be greatly appreciated.

Let me know if you require any other information from me.

Regards,
Jannie

 

[John Robertson]

On 2019/08/26 3:11 a.m., janniebrand@gmail.com wrote:

Hi Folks

I have a Commax CDV-43k/DRC-4L (Stock Code: PI-1176) intercom that isn't working anymore. It seems the power supply board in the intercom (CDV-43K) itself (converting wall power of 220v to 15v) has blown. I think it might be the transistor (see photos: https://imgur.com/a/uBCXjwQ). The suppliers say that it is out of warranty and that I would have to buy a new one.

Here is a link with a few photos of a circuit board that isn't working anymore:
https://imgur.com/a/uBCXjwQ

I have tried searching online, but couldn't find anything that gave me any indication of the specs of the transistor or what transistor to try and replace it with. I also tried to search for the schematic, but couldn't find anything.

If anyone can perhaps help me identify the blown transistor or perhaps point me in the right direction that would be greatly appreciated.

Let me know if you require any other information from me.

Regards,
Jannie

Actually the PCB silkscreen indicates that this is an IC as it is called
"U2", instead of a "Q" designation - Q for transistor and U for IC is a
common convention. I would then suspect it may be a 15VDC regulator as
this is some sort of switch mode power supply.

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."

 

[pfjw@aol.com]

On Monday, August 26, 2019 at 11:09:15 AM UTC-4, John Robertson wrote:

Actually the PCB silkscreen indicates that this is an IC as it is called
"U2", instead of a "Q" designation - Q for transistor and U for IC is a
common convention. I would then suspect it may be a 15VDC regulator as
this is some sort of switch mode power supply.

John :-#)#

And if this is the case, a TO-92 package, 15+ V regulator is here:

https://www.newark.com/on-semiconductor/mc78l15abpg/ldo-voltage-regulator-15v-0-1a/dp/42K1178

Same source for a 15- V regulator as well.

Peter Wieck
Melrose Park, PA

 

[jfeng@my-deja.com]

On Monday, August 26, 2019 at 9:03:07 AM UTC-7, pf...@aol.com wrote:

On Monday, August 26, 2019 at 11:09:15 AM UTC-4, John Robertson wrote:

And if this is the case, a TO-92 package, 15+ V regulator is here:

https://www.newark.com/on-semiconductor/mc78l15abpg/ldo-voltage-regulator-15v-0-1a/dp/42K1178

Same source for a 15- V regulator as well.

Peter Wieck
Melrose Park, PA
One more step you can take in an attempt to verify this hypothesis: you might remove the remaining epoxy from the chip and look at it under a microscope. I have seen some chips with part numbers in one of the metal layers. Or you could see that it is too complex to be a simple transistor and complex enough to be a regulator, or something in between like a Darlington.

 

[Piotr Piatek]

W dniu 26.08.2019 o 17:09, John Robertson pisze:

On 2019/08/26 3:11 a.m., janniebrand@gmail.com wrote:
Hi Folks

I have a Commax CDV-43k/DRC-4L (Stock Code: PI-1176) intercom that
isn't working anymore. It seems the power supply board in the intercom
(CDV-43K) itself (converting wall power of 220v to 15v) has blown. I
think it might be the transistor (see photos:
https://imgur.com/a/uBCXjwQ). The suppliers say that it is out of
warranty and that I would have to buy a new one.

Here is a link with a few photos of a circuit board that isn't working
anymore:
https://imgur.com/a/uBCXjwQ

I have tried searching online, but couldn't find anything that gave me
any indication of the specs of the transistor or what transistor to
try and replace it with. I also tried to search for the schematic, but
couldn't find anything.

If anyone can perhaps help me identify the blown transistor or perhaps
point me in the right direction that would be greatly appreciated.

Let me know if you require any other information from me.

Regards,
Jannie


Actually the PCB silkscreen indicates that this is an IC as it is called
"U2", instead of a "Q" designation - Q for transistor and U for IC is a
common convention. I would then suspect it may be a 15VDC regulator as
this is some sort of switch mode power supply.

John :-#)#

It's likely a TL431, but I wonder how it could have blown so violently
without some external help, as it is connected to the circuit through
relatively high resistances?

Piotr

 

[Phil Allison]

janni...@gmail.com wrote:

I have a Commax CDV-43k/DRC-4L (Stock Code: PI-1176) intercom that isn't working anymore. It seems the power supply board in the intercom (CDV-43K) itself (converting wall power of 220v to 15v) has blown. I think it might be the transistor (see photos: https://imgur.com/a/uBCXjwQ). The suppliers say that it is out of warranty and that I would have to buy a new one.

Here is a link with a few photos of a circuit board that isn't working anymore:
https://imgur.com/a/uBCXjwQ

I have tried searching online, but couldn't find anything that gave me any indication of the specs of the transistor or what transistor to try and replace it with. I also tried to search for the schematic, but couldn't find anything.

** Take about 15 minutes to trace that schem yourself.

If anyone can perhaps help me identify the blown transistor or perhaps
point me in the right direction that would be greatly appreciated.

** Looking at the copper side of the PCB, I can see the blown 3 pin device is driving the LED inside the opto-coupler for feedback.

There is a small heatsink behind the chip, so a TL431 is a good bet.

The opto will be cactus too.

What happened ?

Either the opto flashed over ( very rare ) or a foreign metal object did the trick.


..... Phil

 

[whit3rd]

On Monday, August 26, 2019 at 3:11:44 AM UTC-7, janni...@gmail.com wrote:

> I have tried searching online, but couldn't find anything that gave me any indication of the specs of the transistor...

piotr and Phil are correct, it's probably a TL431 (or one of the many clones);
to get it to blow up, takes lots of current (and probably another component
was the cause). Install another TL431, another optoisolator (the four-wire
black rectangle), and certainly check out the
diodes (reverse voltage, if the diodes don't block it, could have done in the TL431).

That looks like a single-sided phenolic circuit board; they can get damaged,
so examination for cracks and some care about stress applied when under soldering
heat are in order. The project can benefit from solder-wick and liquid flux.

 

Thank you everyone for the amazing help so far. I'm learning so much with this.

I feel like I should've perhaps mentioned that I'm pretty much a beginner when it comes to circuit boards. I've replaced fuses, capacitors and resistors before, after doing some research and finding the correct replacement parts, in order to bring back life to old/broken appliances/toys.

Also, something else to note is that the local (Cape Town, South Africa) place where I get all my electronic parts is Mantech (https://www.mantech.co.za).

That said, with regards to the Fixed Positive Voltage Regulator (15+ V) in a TO-92 package (as mentioned by John & Peter), I found the following options:
https://www.mantech.co.za/ProductInfo.aspx?Item=14M8346
https://www.mantech.co.za/ProductInfo.aspx?Item=14M8345
https://www.mantech.co.za/ProductInfo.aspx?Item=14M4528

I've also followed the advice to remove the remaining epoxy from the chip and look at it under a magnifying glass (unfortunately I don't own a microscope).

I have uploaded some new images (viewed through the magnifying glass) to the same link (the new pics are at the bottom):
https://imgur.com/a/uBCXjwQ

There seems to be no part numbers on the metal layers. I'm also not informed enough to know whether it is "too complex to be a simple transistor and complex enough to be a regulator, or something in between like a Darlington".. To my untrained eye it seems pretty simple, so maybe a transistor then?

With regards to the TL431 (as mentioned by Piotr, Phil & whit3rd), I could find a few options at Mantech, but not sure which one could work:
https://www.mantech.co.za/Stock.aspx?Query=TL431and

With regards to the opto-coupler (mentioned by Phil), I've added a photo of that as well (https://imgur.com/a/uBCXjwQ), the code on the opto-coupler is:
L1620
817BL
W

@Phil: If I understood you correct, you are saying the because of the blown part, the opto is likely blown as well? If so, which opto should I try to replace it with:
https://www.mantech.co.za/Stock.aspx?Query=817+optoand

Unfortunately I have no idea what happened as I got this from someone that was throwing it out, since they had already replaced it. I'm trying to see if I can fix it. It is from the handset/monitor side of the intercom system, so maybe it came loose of the wall mounting and took a heavy knock? Also, we have had load shedding happening in the past, which would some times have caused voltage spikes when the power came back on. Don't know if that could've cause something like this to happen? I know people have lost appliances to that, but not sure if it could be related.

@whit3rd: So you reckon, I just try to replace the blown part with a TL431 (any particular one from the list? https://www.mantech.co.za/Stock.aspx?Query=TL431and) and then also replace the optoisolator (any particular one from the list? https://www.mantech.co.za/Stock.aspx?Query=817+optoand)?

I'll do a check of the diodes. Would testing in circuit be sufficient or should I remove the diodes from the circuit for testing?

 

I did a bit of a detailed examination of the board with a magnifying glass for any possible damage.

I found something on the back of the board that I hadn't noticed before (probably because of the blown part on the front). It seems like there might have been a short between a resistor (R20) and a diode (D4). I have taken some pictures and added it to the album (https://imgur.com/a/uBCXjwQ).

Not sure if this helps or makes any difference, but let me know if there is anything else that I can check/try.

 

[jfeng@my-deja.com]

On Tuesday, August 27, 2019 at 2:39:00 AM UTC-7, janni...@gmail.com wrote:

I've also followed the advice to remove the remaining epoxy from the chip and
look at it under a magnifying glass (unfortunately I don't own a microscope).

I have uploaded some new images (viewed through the magnifying glass) to the
same link (the new pics are at the bottom):
https://imgur.com/a/uBCXjwQ

There seems to be no part numbers on the metal layers. I'm also not informed
enough to know whether it is "too complex to be a simple transistor and
complex enough to be a regulator, or something in between like a Darlington".
To my untrained eye it seems pretty simple, so maybe a transistor then?
To my eyes, it looks like there is no remaining silicon there at all (maybe it got destroyed explosively when it blew off the epoxy) and all you have left are the wire leads. The wires alone do not tell you much.

Can you trace out where the wires go? If it is a regulator, then the center lead will usually go directly to ground (nearly zero ohms to the negative output terminal). If it is a TL431, the left wire (looking at the flat surface with the wires down) will probably go to ground. And if it is a pass transistor, then probably none of the wires connect to the ground.

 

[Baron]

janniebrand@gmail.com prodded the keyboard with:

I did a bit of a detailed examination of the board with a magnifying
glass for any possible damage.

I found something on the back of the board that I hadn't noticed
before (probably because of the blown part on the front). It seems
like there might have been a short between a resistor (R20) and a
diode (D4). I have taken some pictures and added it to the album
(https://imgur.com/a/uBCXjwQ).

Not sure if this helps or makes any difference, but let me know if
there is anything else that I can check/try.

Looking at your pictures, the transformer has been very hot at some
time ! Suggesting a heavy load for some period of time.

--
Best Regards:
Baron.

 

On Tuesday, 27 August 2019 10:39:00 UTC+1, janni...@gmail.com wrote:

Thank you everyone for the amazing help so far. I'm learning so much with this.

I feel like I should've perhaps mentioned that I'm pretty much a beginner when it comes to circuit boards. I've replaced fuses, capacitors and resistors before, after doing some research and finding the correct replacement parts, in order to bring back life to old/broken appliances/toys.

useful to know

> Also, something else to note is that the local (Cape Town, South Africa) place where I get all my electronic parts is Mantech (https://www.mantech.co.za).

A lot of parts can be taken from dead e-junk.


> I've also followed the advice to remove the remaining epoxy from the chip and look at it under a magnifying glass (unfortunately I don't own a microscope).

I'd approach it by looking at the circuit connected to it. That usually makes it clear what a part is.

@Phil: If I understood you correct, you are saying the because of the blown part, the opto is likely blown as well? If so, which opto should I try to replace it with:
https://www.mantech.co.za/Stock.aspx?Query=817+optoand

Unfortunately I have no idea what happened as I got this from someone that was throwing it out, since they had already replaced it. I'm trying to see if I can fix it.

With mains stuff it's useful to test it by running it in series with a filament lamp if there's a possibliity of shorting.


> Also, we have had load shedding happening in the past, which would some times have caused voltage spikes when the power came back on.

Lots of mains appliances consume a large current surge at switch on, together these reduce mains voltage rather than cause a voltage spike or 'surge'. 'Surges' is one of those topics on which plenty of misinformation is believed.

> Don't know if that could've cause something like this to happen? I know people have lost appliances to that, but not sure if it could be related.

to all 3 of those points, I doubt it.


> @whit3rd: So you reckon, I just try to replace the blown part with a TL431 (any particular one from the list? https://www.mantech.co.za/Stock.aspx?Query=TL431and) and then also replace the optoisolator (any particular one from the list? https://www.mantech.co.za/Stock.aspx?Query=817+optoand)?

what caused what to blow?

> I'll do a check of the diodes. Would testing in circuit be sufficient or should I remove the diodes from the circuit for testing?

It varies. In-circuit testing will sometimes tell you they're ok, sometimes not. Far quicker than taking time out of course.


NT

 

[Phil Allison]

janni...@gmail.com wrote:

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

With regards to the opto-coupler (mentioned by Phil),
I've added a photo of that as well (https://imgur.com/a/uBCXjwQ),
the code on the opto-coupler is:
L1620
817BL
W

** The "817" part of the number is the main identifier.

I would expect any "xx817xx" opto-coupler part on offer to work.




..... Phil

 

[whit3rd]

On Tuesday, August 27, 2019 at 2:39:00 AM UTC-7, janni...@gmail.com wrote:

> That said, with regards to the Fixed Positive Voltage Regulator (15+ V) in a TO-92 package (as mentioned by John & Peter), I found the following options:

That's an unlikely part, considering it's right next to the optoisolator.

<https://www.mantech.co.za/ProductInfo.aspx?Item=14M7535> is the TL431 part

for the optoisolator,
<https://www.mantech.co.za/ProductInfo.aspx?Item=14M7535>

> I'll do a check of the diodes. Would testing in circuit be sufficient or should I remove the diodes from the circuit for testing?

If the diodes are short-circuited, they'll look bad in-circuit; if a multimeter that does diode check
is available, use that. Otherwise... play around with ranges on an ohmmeter scale, and
find out what a good example diode reads, both forward and reverse, and try to match that.
in a pinch (the diodes look like they're 1N4007) wire 'em in series with two batteries and
a flashlight bulb; should light forward-connected, not backward.

 

[Jannie]

Thank you again to everyone that has been contributing. I really appreciate it so much and I'm learning so much.


> Can you trace out where the wires go? If it is a regulator, then the center lead will usually go directly to ground (nearly zero ohms to the negative output terminal). If it is a TL431, the left wire (looking at the flat surface with the wires down) will probably go to ground. And if it is a pass transistor, then probably none of the wires connect to the ground.

I have tried the above suggestion and the center lead goes to go to ground (nearly zero ohms to the negative output terminal, 1.6 ohms to be exact, but that's the same I get if I directly connect the 2 test leads together). Not sure if this means it's a regulator or if it's still more likely to be a TL431, but I hope this helps.


> With mains stuff it's useful to test it by running it in series with a filament lamp if there's a possibility of shorting.

Thanks for this, I will definitely do the testing with this setup. I'm sure I still have a few old filament lamps in the garage somewhere.

I did some more detailed examination of the board on the front/top side with a magnifying glass for any possible damage and found another part with damage, the other IC (marked as U1 on the board).

The code on IC is:
H11552
OB2358AP
L d

Based on what I found, this seems to be a "Current Mode PWM Power Switch". Not sure which one would be the correct replacement as there are many and not one matching the "OB2358" code (https://www.mantech.co.za/Stock.aspx?Query=PWM+DIL08and). Anyone have any suggestions?

Again, I hadn't noticed it before (probably because I assumed the problem was the clearly blown part). I have taken a picture and added it to the album (https://imgur.com/a/uBCXjwQ). You can see there is a crack in the center top side of the chip running down to the bottom right side.

I also added an image of the front/top of the board with an overlay of the circuit at the bottom. Don't know if that helps anyone, but it's definitely helped me starting to understand what goes where and the connection between the components.

@whit3rd: Thank you for confirming the TL431 part. Not sure if you meant to paste a link for the optoisolator part, but it is the same link as the one for the TL431 part. @Phil did however mentioned that any "xx817xx" opto-coupler part should work.

> If the diodes are short-circuited, they'll look bad in-circuit; if a multimeter that does diode check is available, use that.

I have tested the diodes in circuit with a multimeter and some of them (D1, D2, D3, D4 & D6) looks bad (shorted), but as mentioned, they could be fine.. I can also confirm that the few diodes where I could actually see the number, are in fact 1N4007 diodes. I reckon I just go buy a pack of 10 x 1N4007 diodes with the other parts (once confirmed) and then tackle the diodes tested as shorted in circuit 1 by 1, removing, testing and replacing if needed.

 

[Jon Elson]

On Mon, 26 Aug 2019 03:11:40 -0700, janniebrand wrote:

A lot of these power supplies use some form of a TL431 shunt regulator,
that drives the LED of an optocoupler to control the switch-mode FET
driver.

Jon

 

On Wednesday, 28 August 2019 11:22:26 UTC+1, Jannie wrote:

Thank you again to everyone that has been contributing. I really appreciate it so much and I'm learning so much.


Can you trace out where the wires go? If it is a regulator, then the center lead will usually go directly to ground (nearly zero ohms to the negative output terminal). If it is a TL431, the left wire (looking at the flat surface with the wires down) will probably go to ground. And if it is a pass transistor, then probably none of the wires connect to the ground.

I have tried the above suggestion and the center lead goes to go to ground (nearly zero ohms to the negative output terminal, 1.6 ohms to be exact, but that's the same I get if I directly connect the 2 test leads together). Not sure if this means it's a regulator or if it's still more likely to be a TL431, but I hope this helps.


With mains stuff it's useful to test it by running it in series with a filament lamp if there's a possibility of shorting.

Thanks for this, I will definitely do the testing with this setup. I'm sure I still have a few old filament lamps in the garage somewhere.

I did some more detailed examination of the board on the front/top side with a magnifying glass for any possible damage and found another part with damage, the other IC (marked as U1 on the board).

The code on IC is:
H11552
OB2358AP
L d

Based on what I found, this seems to be a "Current Mode PWM Power Switch".. Not sure which one would be the correct replacement as there are many and not one matching the "OB2358" code (https://www.mantech.co.za/Stock.aspx?Query=PWM+DIL08and). Anyone have any suggestions?

Again, I hadn't noticed it before (probably because I assumed the problem was the clearly blown part). I have taken a picture and added it to the album (https://imgur.com/a/uBCXjwQ). You can see there is a crack in the center top side of the chip running down to the bottom right side.

I also added an image of the front/top of the board with an overlay of the circuit at the bottom. Don't know if that helps anyone, but it's definitely helped me starting to understand what goes where and the connection between the components.

@whit3rd: Thank you for confirming the TL431 part. Not sure if you meant to paste a link for the optoisolator part, but it is the same link as the one for the TL431 part. @Phil did however mentioned that any "xx817xx" opto-coupler part should work.

If the diodes are short-circuited, they'll look bad in-circuit; if a multimeter that does diode check is available, use that.

I have tested the diodes in circuit with a multimeter and some of them (D1, D2, D3, D4 & D6) looks bad (shorted), but as mentioned, they could be fine. I can also confirm that the few diodes where I could actually see the number, are in fact 1N4007 diodes. I reckon I just go buy a pack of 10 x 1N4007 diodes with the other parts (once confirmed) and then tackle the diodes tested as shorted in circuit 1 by 1, removing, testing and replacing if needed.

You asked for a suggestion, I have one. SMPSUs are not the simplest things for beginners, and this one sounds well knackered. I suggest picking up another piece of e-waste & fixing that. You're not gonna fix them all.


NT

 

[Jannie]

> You asked for a suggestion, I have one. SMPSUs are not the simplest things for beginners, and this one sounds well knackered. I suggest picking up another piece of e-waste & fixing that. You're not gonna fix them all.

I have to be honest, I have been thinking the same thing, but I was and still am willing to give a go if it is indeed fixable. It's not like the parts cost that much or like I would be risking breaking it, so even if I screw it up completely, then I'm still at the very least learning something along the way.

I do get your point however and I might just throw in the towel if no one can advise as to which "Current Mode PWM Power Switch" I should try (from this link: https://www.mantech.co.za/Stock.aspx?Query=PWM+DIL08and) in order to replace the current "OB2358" part with or if someone can confirm that it's not a part that you could just replace with a similar part from the link.

Anyway, it's neither here nor there. I just thought I'd give it a go and hopefully learn something in the process, which I most definitely have so far..

 

On Thursday, 29 August 2019 21:48:20 UTC+1, Jannie wrote:

You asked for a suggestion, I have one. SMPSUs are not the simplest things for beginners, and this one sounds well knackered. I suggest picking up another piece of e-waste & fixing that. You're not gonna fix them all.

I have to be honest, I have been thinking the same thing, but I was and still am willing to give a go if it is indeed fixable. It's not like the parts cost that much or like I would be risking breaking it, so even if I screw it up completely, then I'm still at the very least learning something along the way.

I do get your point however and I might just throw in the towel if no one can advise as to which "Current Mode PWM Power Switch" I should try (from this link: https://www.mantech.co.za/Stock.aspx?Query=PWM+DIL08and) in order to replace the current "OB2358" part with or if someone can confirm that it's not a part that you could just replace with a similar part from the link.

Anyway, it's neither here nor there. I just thought I'd give it a go and hopefully learn something in the process, which I most definitely have so far.

I don't think you've got enough info to fix it. You might be lucky but too often power parts are killed by something else going wrong. You've got a relatively complex supply, many fried parts, no idea what caused the failure and you don't know what the parts even are. I'd move on at this point.


NT

 

> I don't think you've got enough info to fix it. You might be lucky but too often power parts are killed by something else going wrong. You've got a relatively complex supply, many fried parts, no idea what caused the failure and you don't know what the parts even are. I'd move on at this point.

Fair enough. Thank you for all the help and info. I have certainly learned a few things, which will help me going forward.

A last question perhaps, would it be worth a try to see if I can find a working 220v AC to 15v DC board and then just swap the broken one out with the working one and perhaps just do some soldering for the connecting wires? If so, is there anything specific that I should be aware of or look out for?