The Sinclair QL Forum

Hi all,

I just received a QL which I was told was working. However, when I connected it to the power supply, there was no sign of life. Upon opening the case I noticed a rather odd looking board in place of the standard 7805 voltage regulator and heatsink. I checked the voltages on the regulator and it read 5V,10V,10V...which seemed incorrect. I then swapped the board for my known working 7805 and heatsink and the QL came to life.

My question is, how should I resolve this?

Thanks

You may consider the Traco Power voltage regulator (a drop-in replacement, no heatsink needed):
https://it.farnell.com/tracopower/tsr-2 ... &source=CJ

That power board is based on this regulator by the looks of it:

https://www.ti.com/product/MC34063A?utm ... lsrc=aw.ds

You should be able to read 0v on the centre pin of the 3 pin connector the board plugs in with, and the two outer pins 9v (probably reading as 10v) and the 5v output for the QL.

Your voltage readings suggest that the 0v is not connecting correctly perhaps?

This looks like a board Sandy fitted to a few systems in 1984.

They're horrible and should not be used. We stopped using them as soon as we got customer feedback.

Who is Sandy...if you don't mind me asking?

Delta wrote: Tue May 16, 2023 8:47 pm Who is Sandy...if you don't mind me asking?

Luckilly we have a wiki for that https://qlwiki.theqlforum.com/doku.php?id=qlwiki:sandy

Oh dear: "WARNING: We have seen at least two models of this regulator and certainly at least one of these has a tendency to overheat and may catch fire! Tony Firshman also reports having seen three at least which have caused voltage surges and destroyed QLs and peripherals."

Fortunately, mine just failed and stopped the machine from starting!

Hi,

I had a couple of these power boards, which were not good, I stored them in the bin.

Glad to see Sandy got something right...