Mitsumi SR151 Overheating, almost burning?

[exxos]

Nope.they are mains filters, to stop switching noise from the PSU feeding back into the mains.

[ziggy]

Hi again,
the correct voltage regulator arrived today and I soldered it in. I now get the correct 5 & 12V after adjusting the voltage-regulating resistor.
The big resistors still get warm, but not as hot as before.
I plugged it into the Mega and turned it on - Nothing, just black screen..
After testing voltages on random ICs on the Mega for about two minutes, the Fuse of the PSU blew with a lightnig arch, about 10cm high I wasn't touching anything while it happened, so I definitely didn't short anything. I immediately pulled the plug and have been thinking since then. What could have caused the Fuse triggering?
Well, Overload most likely - but where and how?
I will measure resistances across the mainboard and see if I can find anything suspicious like very low resistances. Do you have any tips besides that?

@exxos I also noticed, after turning the PSU upside down, a sticker from Mitsumi labels the PSU as SR138 instead of SR151... Haven't noticed that before. Weird. From the looks it seems to be a SR151. Maybe that's just an updated version?

Greetings

[exxos]

I don't think there is a lot of difference between all these anyway. I have not seen many other than the SR98's here.

It sounds like you need a new power supply,If things are really that bad you could may well have blown the motherboard up as well. You would really need a working second machine to swap chips around to see if the main ones are at least working or not.

[ziggy]

Thank you for the input I will definitely run some IC-swapping tests with another PSU and give this dubious PSU to a electrician to take a look. But first I'll be on some business travels for 3 weeks. See you then!

[Tomswork]

From farnnel I think or ebay

NTE Equivalent NTE2348

Tom

[rubber_jonnie]

I dropped a Meanwell PSU in mine, they are quite inexpensive and do a good job. Model is RD50A, 6A @ 5v and 2A @ 12V. I think mine was under £20 from RS.

[ziggy]

@rubber_jonnie

Maybe that's the way to go. Seems to be good quality for the price.

In the meantime, I measured a very low resistance on 5V - GND on the mainboard. Only around 0,3k! 12V seems fine with around 7k. Maybe a short somewhere... Will remove ICs and check for shorts

Greetings

[derkom]

I dropped a Meanwell PSU in mine, they are quite inexpensive and do a good job. Model is RD50A, 6A @ 5v and 2A @ 12V. I think mine was under £20 from RS.

Are you actively cooling that? The Meanwells seem to run pretty cool (and in fact describe themselves as "free air convection" cooled), and I've been considering whether I could get away with sticking one in my TT and eliminating the fan (no spinny drives in here, so no moving parts except that fan). (Although the (recapped) factory PSU is working just fine.)

[rubber_jonnie]

I dropped a Meanwell PSU in mine, they are quite inexpensive and do a good job. Model is RD50A, 6A @ 5v and 2A @ 12V. I think mine was under £20 from RS.

Are you actively cooling that? The Meanwells seem to run pretty cool (and in fact describe themselves as "free air convection" cooled), and I've been considering whether I could get away with sticking one in my TT and eliminating the fan (no spinny drives in here, so no moving parts except that fan). (Although the (recapped) factory PSU is working just fine.)

As it goes, I am actively cooling it, but only because there was already a fan on the PSU frame and it was a simple matter to hook it up. I doubt it needs it.

[ziggy]

On a somewhat related matter, I recently watched a youtube video of Adriens Digital Basement where he updated the notoriously hot internal PSU of a Commodore 1541 Drive. The old PSU produced close to 12W on HEAT in IDLE, compared to 5W with the new one. Working load was around 25W & 14W, not sure on that.
In conclusion: Modern switching PSUs are a treat