exxos's Atari, Amiga & retro forum

I believe I have traced the fault with my Amstrad PSU 12V rail to the SK 3120C voltage dropper IC, but If possible I want to avoid ordering from China.

I verified that there is no 12v output at all, and this chip is where the 12v line is connected to. I also connected my bench PSU up to the 12v line and the Amstrad runs just fine and boots from HDD no problem, so aside from the 12V aspect, the rest of the PSU is delivering as expected (5v,-12v and -24v)

Is there anybody out there in retroland that has some of these ICs, Sanken branded, that they would be willing to sell me as my usual sources (Not China) have come up dry.

Alternatively, if anybody has knowledge of these types of IC and could suggest a viable alternative, that would also work. I have attached the data sheet.

I will look myself but I'm hoping a distributed approach of all the clever people here might get me there quicker :)

Thanks in advance.

Kinda looks like a 7812 but with remove turn on off, is it actually used ? And remote voltage sense, again is that even setup anyway ?

Does this number cross ok SI3120C

Tom

Tomswork wrote: 17 Sep 2020 02:46 Does this number cross ok SI3120C

Tom

Yep, that number is the same item.

@Tomswork

Found some on UTSource, £4 for 10. Trouble is the £20 delivery charge!! I'll keep that as a backup plan, to be fair, UTSource have never sent me duff components.

Managed to locate some on eBay, £8 including delivery for 5, which I ordered, but they won't be here for about 4 weeks. Hopefully they won't be fakes either, but they are like rocking horse sh*t to find, so I had to take a punt.

Will keep digging to see if I can find any modern alternatives in the meantime.

Very frustrating that after all the deep digging and hours of soldering I'm now let down by the PSU. I guess I could try and source a small secondary 12v PSU, but it does need around 1.2-1.3A before the system powers on, anything lower and the HDD wont spin up and the display flickers.

I guess it's the power on surge that is the problem, as once it's running it seems to stabilise at about .8A

EDIT: I also found some on AliExpress. A risk, just like eBay, but they work out about £1 each over both orders, including postage, so worth a punt IMHO. I have a total of 15 on the way, I'm sure I can resell if I need to.

It seems that I have found a UK source 😁

Cricklewood Electronics in the UK seem to be a good source for old components, so I've ordered one and cancelled my AliExpress order. I still have the 5 coming from eBay so I should have spares at least.

Yes sounds good never bad to have a different supplier of the parts other than China

Tom

Tomswork wrote: 17 Sep 2020 18:31 Yes sounds good never bad to have a different supplier of the parts other than China

Tom

Well the part arrived today, so got to give a well done to https://www.cricklewoodelectronics.com/.

Next day delivery, absolutely spot on. That means that if all goes to plan, I can fit it later this evening and fingers crossed it will resolve my 12v output problem, because if not I need to start tracing to the next part inline. A PSU schematic would be nice, but I haven't found one anywhere, and dismantling it to make one is not in the plan!

I a weird follow up on this, the eBay order I had for some of these was cancelled by the seller and I got a refund this morning. It's like they knew I'd fixed it and didn't need the parts any more.

As it goes, I do have a spare now, as the original must have been working all along. Theoretically, since I now know how it's hooked up having traced the PSU, testing it would be really easy to do.

The other thing that made me feel better was that Ben Heck was doing a video repair on a Sharp X68000. Amazing looking machine, but hideously complex inside.

As it happens, he tracked his problem down to a lack of 12V power, and exactly the same sort of plug had failed, only 6 pin not 7. He also spent a ton of time troubleshooting like me, before getting to the cable.

DON'T TRUST THE PLUGS!!!

:headbang:

Yeah, I hate anything with connections :cussing: :cussing: :cussing: