Help identifying a blown transistor

On Friday, 30 August 2019 11:12:37 UTC+1, janni...@gmail.com wrote:
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?

If it's just the supply that's fried who knows, might work. Can you not find other dumped electronics?


NT

 

> If it's just the supply that's fried who knows, might work. Can you not find other dumped electronics?

So I have some good news ... I managed to find AC-DC adapter that I could change the output voltage on and changed it to 15V and figured I have nothing to loose, so I connected it to the main intercom board, which then power up and the screen came on. Seems to be working 100%.

This means that either I have to take out the old SMPS board and just wire this adapter directly to the main board (I suppose not ideal) or I need to find a 220V to 15VDC PCB that will fit in the intercom shell/body (seems to be a bit of a low profile board, since the intercom is very flat).

Thanks for the help and I'll definitely try to find some other e-waste that I could use to learn while trying to fix it as well.

 

[ehsjr]

On 8/30/2019 3:31 PM, janniebrand@gmail.com wrote:

If it's just the supply that's fried who knows, might work. Can you not find other dumped electronics?

So I have some good news ... I managed to find AC-DC adapter that I could change the output voltage on and changed it to 15V and figured I have nothing to loose, so I connected it to the main intercom board, which then power up and the screen came on. Seems to be working 100%.

This means that either I have to take out the old SMPS board and just wire this adapter directly to the main board (I suppose not ideal) or I need to find a 220V to 15VDC PCB that will fit in the intercom shell/body (seems to be a bit of a low profile board, since the intercom is very flat).

Thanks for the help and I'll definitely try to find some other e-waste that I could use to learn while trying to fix it as well.

I think your plan is a good one. Probably the most economical
way to repair the intercom. Maybe you can find an AC-DC converter
on bidorbuy. Here's an example I found on Ebay:
https://www.ebay.com/itm/AC-DC-Power-Supply-Step-Down-Converter-Module-110V-220V-230V-to-5V-9V-12V-24V-/192281280733

Referring to the example above, it might fit if you replace the
caps and bend the leads of the new ones so they lay horizontal.
Assuming the U1 is (or was, before it blew up) a 15V regulator
(which provides only 100 mA), then the example converter
would provide more than enough current at 15 volts.
I don't know what you can get at bidorbuy, but you need
something that provides sufficient current at 15 volts.
The example is mentioned as a reference and a possible method of
modifying whatever you do get to fit.

As to the bad supply, save it in case you decide you want
to learn more about switch mode power supplies at some
point in the future. It's nice to read a description of
a circuit and then look at an example of the circuit
you're reading about. Doesn't matter that your circuit is
broken - you know that at one time it was a properly
working switcher. You'll be able to actually see and
identify the various functional portions that are described
in the text. The light bulb turns on "oh, so that's the
common mode choke" or "oh that's the PWM (Pulse Width
Modulation) controller" or "oh that's how they control
the output voltage", etc.

Thanks for starting what has been an interesting thread!
Ed

 

On Friday, 30 August 2019 20:32:02 UTC+1, janni...@gmail.com wrote:

If it's just the supply that's fried who knows, might work. Can you not find other dumped electronics?

So I have some good news ... I managed to find AC-DC adapter that I could change the output voltage on and changed it to 15V and figured I have nothing to loose, so I connected it to the main intercom board, which then power up and the screen came on. Seems to be working 100%.

This means that either I have to take out the old SMPS board and just wire this adapter directly to the main board (I suppose not ideal) or I need to find a 220V to 15VDC PCB that will fit in the intercom shell/body (seems to be a bit of a low profile board, since the intercom is very flat).

Thanks for the help and I'll definitely try to find some other e-waste that I could use to learn while trying to fix it as well.

Great news. Reminds me of a Sony TV with a large PSU board. Replaced the lot with a rectfier, caps & lightbulb.... as an experiment. It worked, but not ideally.


NT