Sourcing power transistor for A500 PSU in the EU
 

Hey!

I seem to have got one of the more rare A500 PSU designs out there since I can't find any references online.
It's a switching (light) model with 4.5A output on the 5v, says "Made in India" on the back.

I have concluded that the switching transistor is shorted. The type model is MJE18006 (https://www.digikey.co.uk/en/product...E18006/1481813).

Mauser and Digikey got a replacement called MJE18008G but the shipping and handling is 10x the price of the transistor.


Happy for any suggestions.

Cheers

Perhaps Elfa ? They are very expensive but still as you are from Sweden then there is a chance that overall cost can be lower... or you need to search local component store but they are unobtainum nowadays... people buying components in internet.

https://www.ebay.co.uk/itm/165866133420

This is ebay uk .

TME suggests this alternative: https://www.tme.eu/dk/en/details/nte...e-electronics/

Their shipping fee is generally lower than farnell, rs-online, digikey and mouser.

You can order direct from LittleDiode as well rather than going through their eBay store - it's usually a bit cheaper that way.

Thanks for the tips guys!

ELFA don't seem to carry that one, nor any suitable replacements as far as I can tell though.

I'll check Little Diode and TME as well.

That actually looks like a viable alternative.

I don't know much about transistors, but it seems like modern transistors have much lower specs in general, which makes it hard to find a suitable replacement. Or am I just looking at the wrong specs?

Not sure what specs you're referring to, or if it's in general?

I've been mostly comparing specs like voltage, current and effect ratings, like the ones on here: https://www.onsemi.com/pdf/datasheet/mje18006-d.pdf. But I'm not sure what parameters are really relevant for my use case.

For instance: this was suggested as a replacement, and a much cheaper one at that. But I can't tell whether it's a suitable replacement or not. Some parameters have lower specs than the original; https://eu.mouser.com/datasheet/2/38...8d-1848960.pdf

It is difficult nowadays as simply silicone vendors ceased production for many transistors - this is PITA - bipolar transistors was annihilated by MOSFET's and IGBT's so your options are quite limited.

In this kind of applications you need to search transistor with same or BETTER parameters, VCEO must be same or higher (so in your case 450V is minimum but i recommend to search for at least 500..600V to get safe reserve - another parameter is breakdown voltage i would say 700..800V minimum - higher better), collector current (IC) at least 6A and power dissipation (at least 100W), TO220 package, additionally current gain may be important (between 10 and 40) and switching speed (dynamic characteristic with capacitance's - input and output).

TME has very limited options - not in stock and unknown quality (China made) but cheap BUJ403A - worth to try, or in stock , more expensive and worse different package (bigger so you need to improvise) BUV48A or FJL6920 .

Btw BUL58D has integrated diode - it may NOT work in your application.

For cross reference https://alltransistors.com/crsearch....ps=TO220&cf=on options are also limited.

Thanks for sharing your insight, @Pandy71, much appreciated.

Would this be a good substitute? It seems to be the bigger brother to the original part: https://www.ebay.de/itm/334059668683

For now it seems like the best bet. And free shipping?! :crazy. Edit: within Germany only of course

MJE18008G should work - better from Germany than nothing - don't know anything about Sweden electronic component distribution reality - i've recalled Elfa from middle of 90's so it was my first proposal but nowadays this is different story.

In Poland i was able to found MJE18008 in https://sklep.gembara.pl/pl/searchqu...5?url=mje18008 - cost slightly above 1E - this (Gembara) is old company - probably selling their stock before ceasing activity (my assumption) also you can try here https://www.podzespoly-elektroniczne...uct/1543ceff58
btw both companies are rather small, niche type so i'm almost sure if they exist in Poland then perhaps similar exist also in Sweden... i hope at least.
Third source https://www.micros.com.pl/en/product...307.html?_gl=1

Thanks for these excellent suggestions.

It's frustrating though. No matter what it will be just shy of €20 with shipping, and then I'm not even sure I will have a working PSU afterwards as there may still be damaged/broken components. While a new Mean Well drop in PSU is just €35.

I'm all for fixing up and keeping things as original as possible, but this one is becoming motivationally challenging.

If you asking me i would go for Krashan advice (another thread https://eab.abime.net/showpost.php?p...2&postcount=12 ) - this probably more reasonable solution (also i expect higher power quality - Commodore PSU are made on cheap).

I'm considering going with this one. Similar specs as the one suggested by Krashan but slightly smaller: https://www.electrokit.com/en/switch...an-well-rt-50b

Should just fit inside a A500 PSU case. Any thoughts?

I noticed it's spec:ed as 5A on the 5V line above, but in fact it's only 4A. But it should be enough even for a A1200 with 030 accelerator, shouldn't it? Even a maxed out A1200 draws only 3A according to Ian.

FYI I ended up with the Mean Well RT-50B. Fits perfectly inside the original case. I used some adhesive velcro to fix it to the bottom, but can still be detached if needed. The PSU runs fairly cool.

It's a tad bit noisy though (as in audible noise) and I got what seems like a horisontal 50 hz "wave" slowly moving vertically over the screen when connected to my TV via scart. Something I haven't noticed before. It's barely visible but it's there if you look for it. It's not there with the C128 + original PSU.

Check if by accident you not swapped L with N - you can use neon probe (hope i use correct name) or any electrician tester - probe to verify if by accident there is no line level potential at ground (shield).

Interesting idea, we have "schuko" plugs here in Sweden, so the actual L and N depends on the orientation in which you plug your connector in, as the socket is not polarized. I'll try to flip the plug next time I hook up the PSU and see if the wave is still there.

Definitely worth to try.