Help identifying this power supply? - Page 1
Forum section: electronics / projects

author: XR
author_rank: Contributor
timestamp: June 21, 2023, 07:52:12 am
content: First of all, I am but a lowly Mechanical student so forgive my ignorance of the arcane art of electronicals.I bought an Extron VSC 100 video scan convertor on eBay from a vendor that normally sells aircraft parts. Normally, they are equipped with universal mains voltage power supplies with an IEC C13 kettle plug on the back labelled for 100-240V at 50-60Hz. The instruction card that came with it and the accompanying online documentation all have the kettle plug pictured. However, my unit instead came with a blanking plate and strain relief for an integral power cord, which is braided and has two very thin white plastic insulated wires in an asymmetrical connector. This makes me wonder if it may have been modified or optioned from the factory with a low voltage AC or DC power supply. The printing of “100-240V 50/60 Hz” above the power inlet is still there, but I am inclined to be skeptical of its veracity given the undocumented power cable and anaemic little wites. Regardless, how can one identify what kind of power supply is inside? What I should connect it to so as not to explode it? Does anyone recognise the connector?Any help is appreciated.

author: XR
author_rank: Contributor
timestamp: June 21, 2023, 07:54:28 am
content: Internal picture of power supply board

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 21, 2023, 08:31:20 am
content: That looks like Molex .062 connector. That and the circuit inside definitely indicate it doesn't accept any mains voltage.Probably 24VDC, but surely better just ask the seller?

author: XR
author_rank: Contributor
timestamp: June 21, 2023, 08:51:21 am
content: Thanks for your reply! Unfortunately the vendor says they don’t know, as they bought it as part of a lot. I have sent an inquiry to the manufacturer but as the product was discontinued decades ago I am not especially optimistic about my chances for a reply. The connector you pictured looks promising! Is there some way I can tell based on the circuit board whether it’s likely to be 24V or 12V or something else? I know some other Extron Video Scan Converters from previous and subsequent generations were powered by daisy-chained 12V DC, but the connectors on those all look different, which is why I am hesitant to assume that as well.

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 21, 2023, 09:04:32 am
content: Can you remove that power supply daughterboard and take a photo of its back? If that PT6304 is regulating for the whole board then it can take 16-30VDC input. It'll be a bit trickier if there's something else taking the input voltage directly.It's going to be a guesswork without proper documentation or checking other example of the same product with internal PSU.

author: XR
author_rank: Contributor
timestamp: June 21, 2023, 11:03:19 am
content: I will do that when I get home and post photos. Thanks

author: XR
author_rank: Contributor
timestamp: June 21, 2023, 12:34:22 pm
content: Here are some closeups if the PSU board including the reverse side. The tiny board could not be removed without desoldering.

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 21, 2023, 05:58:44 pm
content: It doesn't look like there's any direct line between Vin and the output connector so you're probably fine supplying it within PT6304's spec (16-30V, preferably 18-24V). J1 cable is the positive one.Stuffs on the right looks like fuse, reverse voltage protection, filter and TVS. Some weird thing with U2, probably aux rail?Also, who the fuck design PCB like this? What's with the supertinypads and thermal relief?

author: coromonadalix
author_rank: Super Contributor
timestamp: June 21, 2023, 06:34:09 pm
content: here's the datasheet

author: tooki
author_rank: Super Contributor
timestamp: June 21, 2023, 06:44:59 pm
content: It certainly looks like it’s intended for DC. If it’s from passenger aircraft, it’s likely intended to be powered from the 28V DC bus.What are the markings on U2? The three colors on the output connector make me think it’s got two output voltages, so I’m guessing U2 is another regulator of some kind?

author: XR
author_rank: Contributor
timestamp: June 22, 2023, 04:28:44 am
content: Thanks for the info, guys. Here is a closeup of U2 and a wider shot of the PSU in context inside the device.

author: XR
author_rank: Contributor
timestamp: June 22, 2023, 02:20:59 pm
content: The printing on U2 says:88ABLM2661MHope this is of some use.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: June 22, 2023, 02:28:23 pm
content: Try to read the capacitor voltage ratings at the input

author: glarsson
author_rank: Frequent Contributor
timestamp: June 22, 2023, 02:31:00 pm
content: LM2661, voltage doubler or voltage inverter.

author: XR
author_rank: Contributor
timestamp: June 22, 2023, 02:58:00 pm
content: Of the two large capacitors only one can be read due to the gluey schmoo, and it says 63V 100 μF.

author: tooki
author_rank: Super Contributor
timestamp: June 22, 2023, 04:45:37 pm
content: Quote from: XR on June 22, 2023, 02:20:59 pmYep.Without reverse engineering the circuit to see for sure whether they’re doubling or inverting, my guess is that they’re using the LM2661 to create -12V from the +12V rail.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: June 22, 2023, 04:56:58 pm
content: Quote from: tooki on June 21, 2023, 06:44:59 pmThe 63V 100 μF capacitor found might be a confirmation of this theory.

author: XR
author_rank: Contributor
timestamp: June 23, 2023, 03:14:59 am
content: Would it be safe to remove the power supply unit and measure the output voltages while gradually increasing the input voltage until the output voltages reach what seem like reasonable values or could this potentially damage the unit?

author: Terry Bites
author_rank: Super Contributor
timestamp: June 23, 2023, 12:20:13 pm
content: So did they take the power supply out or just rip out the power inlet?I'd buzz out that connector and find ground.Power it from a lab psu. Slowly crank it up from 5V in 1V steps 5V until it works properly.I think a lot of responses are right, it will likely be 12 or 24(28)VExtron say it uses 15W, so set the psu current limit to 1.3AMost hospitals will have a medical equipment mangement lab with a suitable bench psu and grumpy tech on hand.

author: XR
author_rank: Contributor
timestamp: June 23, 2023, 01:25:04 pm
content: Thanks for the reply, Terry.I'm not sure precisely what you mean by the first part of your comment. I 'm not familiar with the term "buzzing out" or what you mean about the the power supply/inlet. I imagine the usual arrangement with the mains voltage power supply has the case earthed but since there are only two conductors now, I must assume either it is not earthed or that maybe the case is connected to negative like a car? (Forgive me.)I strongly suspect this was some weird not-available-to-the-consumer option from Extron designed for installation in an industrial or commercial setting, possibly on an aircraft or as part of a CCTV system, or even in a broadcast setup in a rack in parallel with other devices. I don't know that this particular unit ever had the standard mains voltage power supply in it, or if it did it seems to have been seamlessly removed.I can ask around at my university to see if one of the techs could be bothered helping me and to see if I can borrow a bench power supply.To confirm what you're saying, you mean that I should start at 5V DC hooked up as per ArdWar's comment with J1 as the positive, and increase in increments of 1V until the output reads what? how should I ascertain when it has reached the correct operating voltage? Is it too risky to have it plugged in and operating trying to do its scan-converting thing while the power is being ramped up?I would be glad to hear your thoughts.