Test Equipment [Closed] EPROM Eraser UV141; Fault

Posted by: @crustytv

↑

@cathovisor you're a star Mike, I cannot than you enough, one ordered.

Flattery will get you everywhere Chris, but I hope you've checked the pin spacing before ordering! I did see the current RS offering, but at a whopping £22 plus VAT... 😱 

22 UK pounds! Outrageous!

Have a look at this and do the currency conversion:

https://www.altronics.com.au/p/m7052a-powertran-5va-6+6v-pcb-transformer/

Works out about 7 UK pounds. The difference buys a lot of shipping!

@irob2345 The one I linked Chris to is GBP7.68 (including tax) AND made in Britain too. So no carbon consequences of dragging something halfway round the planet either.

You could always go super cheap!

I used that type of EPROM eraser at several jobs in the late '80s. I last worked on a project that used EPROMs in 1991 - it's been Flash all the way since then.

John

Posted by: @cathovisor

↑

Chris, but I hope you've checked the pin spacing before ordering!

I did, 5 mm pitch, and it arrived today.

However, what the listing neglected to say was the primary and secondary lead-outs are opposed to the original. The easiest way to describe this is the original TX being left-handed, the new being right-handed. Meaning I can get the primary to align not the secondary, or the secondaries but not the primary

 This is the only solution I can come up with, thankfully there are bags of room to do this, not elegant but needs must.

p.s.

The transformer states 0 115V 0 115V on the primary, am I to assume this is OK as the PCB strapping the two middle pins together? The old TX gave details, this one does not.

You need to put the two primary 115v windings in series. Connect 240V to the outer pins and connect the two inner ones together as you said. With the secondary looks like there is a rectifier on each end of the windings, if so then the two inner connections will be joined and grounded

Almost ready to install

It's alive !!!!

@crustytv Indeed - when I looked at the datasheet I saw that arrangement...

Well, my excuse?  I don't have one! I really shouldn't have been dabbling with electronics, most reckless of me, but I needed the distraction, or thought I did. By the following morning, I was at my wits end, thankfully I got to see a nurse (2nd appointment of the day) Friday morning, who revealed I was running a temperature due to a nasty case of uvelitis, coupled with a double ear infection. Not surprised, I made mistakes my mind was in a total fog, in part to the pain, lack of sleep, food and water. Thankfully on the mend now.

@crustytv 

Glad you on the mend, hopefully a quick recovery.

@crustytv Euch, that's a horrid combination you've got there - and I thought I was hard done by with jaw/ear pain from impacted wax!

No matter, I think the original transformer was a bit wimpy anyway so the 6VA one will serve you better.

Er, why didn't you just drill a couple of extra holes in the PCB?? The secondary would have been the best place to do this, surely?

@irob2345 Then think of all the track cutting and linking to connect the now-offset pins to their correct tracks.

Also being 6VA the TX was a little larger than the original 3VA, whilst the primary holes would align, I could not drill the PCB for some of the secondary as it would have been through another trace. If that was not enough hassle, due to the increased TX it would now be obstructed by two diodes.

As @cathovisor rightly pointed out (who didn't need justification, for my course of action), yes, I could have gone about drilling, cutting, moving and generally abusing the board's originality, or I could leave it well alone and install a daughter board.

All easily reversed if someone in the future wanted to fit an original spec'd TX. Which by the way I now have, I found the exact RS new old RS stock one, but I'll leave that off in light of catho's recommendation.

@crustytv It's an annoying feature of low-powered mains transformers that it doesn't take much to make them fail. The most recent case I had to deal with was a tiny thing - probably less than 2VA - in an active equaliser for a loudspeaker. In this case, I had no choice but to remove all the PSU components and replace it with an encapsulated miniature SMPSU, stuck with double-sided foam onto the PCB in the cleared area.

I hope it never gets dropped!

So do I, as the UV tube would certainly break into many pieces, perhaps that was equally worth noting in the event of a drop rather than just focusing on the new TX arrangement.

I've far more confidence in the TX work I've performed, surviving a drop. It is secured with tiered PCB stand-offs, through the existing PCB, all the way down the metal sub chassis. However, if it were to break free in the event of a drop, it is isolated from the glass tube below by the metal casing sub chassis above. Though, as I said above, any drop is going to result in that tube smashing.

I agree accidents happen, I move many CRT TV's about from the museum to the bench, some TVs are super rare like the 4K's. Shall we say every time I move one, "I hope you don't drop that". There's more chance of me dropping a TV than me ever dropping the EPROM eraser, which has now taken up permanent residence on the store bench, I doubt it will ever move until I'm put 6ft under.

This was a £100 second-hand dead on arrival piece of lab equipment, it now works, and has an uprated TX that is easily removed and reverted to original. In my book, that's the positive to take away from this thread.