Re: PB70 AT power supply
For sure, I did another one a while back, the whole board was covered in wet dust from the caps, though it cleaned up fine and after replacement of the capacitors it came back without a problem. This one has been the hardest repair attempt I have tried. I have never had something clearly not show signs of a failure, yet still wont start up. I'm still thinking its the photothyristor not working properly. Once I know the transformer is working properly, I will replace that and then start replacing all the other semiconductors because that's all that remains....
Zorix
Member
Last Activity: 09-30-2022, 09:20 AM
Joined: 09-19-2013
Location: Fort Myers
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Re: PB70 AT power supply
One is the optocoupler, 4 pin, and the other is the photothyristor coupler (s12md1v - ), 6 pin. It doesn't require a load, I do have another one of the same model in another machine and it outputs without any load.Leave a comment:
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Re: PB70 AT power supply
Well there is no standby since this is AT, so it's manually switched on at the primary input side. I should clarify I used one of those 3 pin component testers to check the transistors and it identified all the parts correctly and around 700 or so for Vf on the transistors. Though it detected the photothyristor as a transistor with or without turning on the LED side. However I also manually tested that using continuity through the anode and cathode and it turns on when the LED is turned on. I don't know for sure if it's completely good, don't really have...Leave a comment:
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Re: PB70 AT power supply
I replaced all electrolytics except for the bulk filtering ones. The blue one as well, though they actually had a good ESR rating and capacitance was spot on. Thanks.Leave a comment:
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PB70 AT power supply
I have an AT power supply (custom for a specific computer model) and it does not power on. I have had some experience repairing power supplies so normally it's not a big deal. First thing I noticed is the fuse is not blown, however it does not output any power. I have checked for shorts on the secondary side, checked all the transistors, including the main switching transistor, all the diodes, the optocoupler and photothyristor seem to work. I get voltage, about 300vdc, if I remember, at the primary side bridge rectifier. I have even checked all the resistors and they are at the rated value. From...Last edited by Zorix; 06-21-2018, 10:44 AM. -
Re: s18k150 MOV replacement
Thanks. Best match I have been able to find would be: [url]https://www.digikey.com/product-detail/en/S20K150/495-1416-ND/593850?curr=usd&WT.z_cid=ref_octopart_dkc_buynow&site=us[/url]
That was a better datasheet than I was able to find, so that's much appreciated!Re: s18k150 MOV replacement<br /> <...tter datasheetLeave a comment:
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Re: s18k150 MOV replacement
Thanks Dgtech. I figured this would work as well but it's not needed at the moment, just keeping it as a working backup. Strange part was this MOV was on the protected backed up side so I think something took a surge from another point and came back into the UPS. Tested every other semiconductor for shorts and everything else seems fine, other than a small 1A fuse near one of the transformers showing as open, but no visible damage to any component.Leave a comment:
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s18k150 MOV replacement
I picked up an APC UPS (BK650) a while back that was was not providing any power output. I have done a few APCs before so I don't have a problem getting in there and looking for problems. I found a shorted out s18k150 MOV which appears to be a unit made by Siemens. I haven't been able to find a replacement and It's not a part of the circuit I have much experience with so I don't know what would be a suitable replacement. I know its an 18mm disc, and a 20mm would fit, but I don't know how this would affect it's protection capabilities. Any help would be appreciated. Thanks. -
Re: APC Back-ups RS 1500 Dead
I know this topic is a little bit old but I think this could help. A common problem in the BR1500 model is that two surface mount aluminium electrolytic capacitors (C40 and C41) responsible for the -8v supply to the line sense circuit is marginal or failed. On mine, they read correct 22uF value but fail on ESR test. Replacing either or both of these should fix the on battery always or constant switching to battery.
I also have a PDF of the schematic for the board model 640-0253E. I don't know about this forum's policy though. APC has shut...Leave a comment:
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Re: Samsung LN40D550 Power supply short circuit
Thanks guys. I was able to replace both mosfets and the driver chip and everything came back up again.Leave a comment:
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Re: Samsung LN40D550 Power supply short circuit
I was able to finally read off the chip model. I found it to be a Fairchild Semiconductor FAN7930B. Is there a way to test this chip to know if it's faulty? Thank you.Leave a comment:
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Re: Samsung LN40D550 Power supply short circuit
Thanks Martino, I'm going to have to look for one of those. That's really handy for sure. I was just using the magnifer on my clip thing that I use to hold boards and wires and such. Using a few types of flash lights only produced glare and not much detail. I did make out what looked like FAN on it near the middle but that's about it.Leave a comment:
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Re: Samsung LN40D550 Power supply short circuit
Alright thank you. Thats what I was wondering. It's a surface mount 8 pin chip it looks like. However, I cannot seem to read the writing on it. I wish I had a nice camera to take a close up of it. I have really good sight but I can't make out anything on it. Are these standard ICs or are they all different? Would be really nice if I had a schematic for it but haven't found one yet. Thanks a lot for your help guys!Leave a comment:
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Re: Samsung LN40D550 Power supply short circuit
That could be right. My multimeter might not be able to read such low values accurately. Any ideas what else could be causing the shorts?Leave a comment:
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Re: Samsung LN40D550 Power supply short circuit
After a little bit more testing, I found a 5 Watt resistor of unknown ohms showing no resistance at all. It's connected to both MOSFETS from the source pin to the negative side of the rectifier. So far this could be another symtom of another issue or part of the cause. Sadly, I can't find any information about it. The part is labeled with: MPR-5W R070JSMT. Any ideas?Leave a comment:
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Samsung LN40D550 Power supply short circuit
Hello Everyone.
I have been attempting to repair a Samsung LN40D550 board that is blowing fuses. I have founde one of the power MOSFETS (10NM60N) shorted out. It's in parallel with another of identical type. I read the forum on [url]https://www.badcaps.net/forum/showthread.php?t=22919[/url] and one of the guys there removed the MOSFET and powered on the TV and had no problems. As a troubleshooting test, I removed it and tried the same. It blew the fuse and the remaining MOSFET as well. Now I'm not sure if it was because the circuit is different and needed the second one to function or something...Last edited by Zorix; 09-19-2013, 08:44 PM. -
Re: New Members - please post your introductions here
Hello everyone. I am a new member to this forum, however I have read quite a bit over time and found the information useful. I have repaired computer motherboard and monitor power supply boards with bad caps and transformers. I figured it would be good to sign up to ask a question. Thanks everyone!Leave a comment:
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