Building a replacement MTX PSU

[gunrock]

Yes, Martin, Mark and Bill that was it. Opened the case and the keyboard pcb end of the cable was off by one pin (unconnected pin was to the left, as viewed looking from end of the MTX with the external edge connector). I didn't notice, but I must have done this when I reassembled after the (very necessary) deep clean of the keyboard.

Point taken Mark, about double-checking before hitting the power button. And yes, the reset buttons did work when pressed even with the cable off by 1 pin.

20210209_143439.jpg (78.8 KiB) Viewed 38713 times

Thanks again folks. I'm going to teach the kids a little Memotech basic tonight and next, I'll need to think about getting a CFX.

[Dave]

As Steve noted previously, the transformer that Mark used in his design is no longer available from Rapid (it’s no longer made).

I’ve just had a user from Italy ask me if I know of a replacement, I don’t, but can Steve advise what replacement he used or can Mark suggest an alternative please?

Regards
Dave

[gunrock]

Hi Dave,

The transformer I used was an Indel transformer which is still available (just checked) from tme.eu, which is where i bought it:

https://www.tme.eu/dk/en/details/ts40_0 ... /ts-40-020

It is currently about 18 EUR plus VAT for Italy, whatever that happens to be.

Steve

[Dave]

Hi Steve,

Thanks a lot!

Regards
Dave

[1024MAK]

Yeah, I don’t know of anything else that is suitable. The important point being that an alternative transformer has a suitable primary for your mains voltage and either a 7.5V - 0 - 7.5V centre tapped output, or dual 7.5V secondaries. The “power” rating should be 40VA or above.

If you go to the manufacturers web site (link) they still list part number VTX-126-050-2075. But that does not mean that any are currently available.

As the increasing use of switch mode power supplies (SMPSU) continues, manufacturers of conventional transformers are becoming more limited in the range they have available

One alternative would be a redesign, using two transformers. Or one transformer and a separate SMPSU. But then things get even more bulky…

Another possible alternative to the design detailed in this topic, would be to use a completely different technique. But that would be a whole different story…

Mark

[1024MAK]

Please note, above post has just been edited…

[Dave]

Thanks Mark,

As you say, Vigortronix do still have them listed, but they are not a stock item. They would be able to do a special order for a MOQ of 10 at a cost of around £25 each (+VAT I guess), so there is an option should 10 people be interested (unlikely)

Regards
Dave