- Help identifying a blown transistor - 3 Updates
| janniebrand@gmail.com: Aug 30 12:31PM -0700 > 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 <ehsjr@verizon.net>: Aug 31 02:37AM -0400 > 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 |
| tabbypurr@gmail.com: Aug 31 01:17AM -0700 > 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 |
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