ALC68A PSU Strip down & clean up

[smogthemog]

As most will know I have successfully stripped down, cleaned, re-painted, re-assembled and re-aligned an ALC68B Laser head just recently but after one of the capacitors nearly exploded on it's accompanying PSU at the UKLEM just gone, I thought it was about time I set too and started the same strip down and clean on the aforementioned PSU.
The capacitor failure was caused by the crimp terminals on the wires connecting to the cap being loose and drastically overheating. This damaged the inside of the cap and caused it to crack around the terminal exit and the bubble and spit during usage with heavy current draw. I had to terminate use if it at the LEM as I didn't really want to be clearing up all the mass from one of those monsters exploding (1600uF @ 350vDC).
I started to strip down the PSU ready to have all the ally bits bead blasted and on their return, have them silver oxide spray painted. Most of the larger caps throughout the PSU are being replaced as some of them are rather old now and I don't want to take any chances.
I am also considering replacing the two large contactors, depending on the outcome when I strip them down. If the contact in the contactors are OK then I will just clean them and re-fit them.
As you can see from the photo's it was in a bit of a poor state and was in desperate need of a clean.
It is now all dismantled and ready for the off. The white front panel will be bead blasted then re-powder coated in white. I then need to find suitable stenciling to re-apply the lettering. If anyone has any suggestions on this, I am all ears

In the last photo, it shows the paxolin board on the rear of the panel meter (by the way, if anyone has one of these meters I WILL purchase it... Mine has a crack through it ) This PCBoard has a small resistor on it, R2, which on mine has been totally burnt out. I wish to know the value of this resistor if anyone has a schematic diagram please. It's the small resistor just to the bottom left of the left hand meter bolt/nut.

Thanks
Jim

[Lasermad]

Fantastic ! love to see the innards of these things ... yer a brave man ...i suppose the dissasembly is the easy bit ...looks like fun though !

PAUL

[Jem]

Jim

Re: The lettering. Have you considered using 'Letraset'. This isn't as popular as it once was, however, it is still available from office supply shops. You buy sheets of assorted letters on a backing paper and by placing them on the object and rubbing the backing paper the letter can be transferred to the object. It's then best to apply a final coat of clear varnish to the entire panel to protect the letters.

The other alternative is to use a cheap label machine (available from Staples etc) and use clear label tape with it. You produce a label with whatever you want to say on it. Peel off the backing tape and apply it to your panel.

I've used both ways many times. The Letraset makes a nice job but is a bit fiddly and you must apply varnish for protection. However, this looks extremely professional. The label machine/clear tape is a quick and dirty way that gives satisfactory results without too much effort.

There is a final option... Silkscreen printing. This is how the professionals do it. If you have a small local friendly silkscreen printers you could probably pursuade him to do a 'one off'. It may be quite expensive though as there is quite a bit of setup time involved.

Cheers

Jem

P.S. Sorry you weren't able to effect a repair at the meet with the connectors, it was worth a try though

[smogthemog]

Thanks for the Crimps Jem, was good on yer

Unfortunately for me though it was too late as the damage had already been done to the capacitor.

Letraset is the way to go I reckon and as you mentioned, varnish it afterwards. I used it years ago on a PSU I built while working at Rumbelows Service Center in Boston. It won me the apprentice of the year award

The ally is going off for blasting today, just so happens we have a load of stainless going off to be surfaced so my lot will be in with it

[smogthemog]

Update on the PSU:
All the Ally case parts and brackets have been blasted and sprayed with Zinc oxide to protect them from corrosion. I am currently waiting for the front plate to come back from being re-powder coated in white. The 2x contactors have been fully overhauled and the capacitor bleed resistors, that sit on top of one of them, have all been replaced. It should have had 3x 100ohm 20W wirewounds across the terminals but one of them was only a 5W resistor and was found to be open circuit, and rather burnt too!. I have replaced them all with new gold alloy 100ohm 25W ones.

The main caps have been replaced, thanks to a very kind forum member and everything else thoroughly cleaned. The transformers have also been cleaned, de-rusted, sprayed and lacquered.
The large heatsink/power transistor assembly has had all it's capacitors replaced for new ones and all the soldering has been re-newed.
The 2x PCB's have also been overhauled, capacitor and soldering wise and the contact pads cleaned with a fibre brush. The small driver PCboard originally had a small 5A bridge rectifier on it. This had been removed and a dirty great 30A type had been stuffed in it's place but it was mounted upon the inside of the front panel, wired back to the board with 2.5mm square section red wire, using a horrible rusty bolt right through it's middle and through the front of the front panel. This has been removed and the correct BRec has been fitted.

I have also got two new top and bottom cover plates as the old ones where gouged and suffered from distortion during the blasting process. I have also gone to 3mm ally plate, from 2mm, to add a bit of rigidity.

I am starting to slowly reassemble all the parts now but still have the meter and one of the MCB's to overhaul.

All in good time

I know it's not a laser overhaul and not quite as interesting as the 68 head but it will look the dog's danglies when it's done

Pimp my laser
Pimp my PSU

[stanwax]

As ever Jim smashing work you are doing
It may not be a laser but I for one am very interested in seeing the job as it goes, especially with your quality of finish.
Cant wait for the next installment

Rob

[Carl B]

As Rob says

Keep the installments coming Jim.

Carl

[smogthemog]

I have had a full day in the shed today. Started in there at six this morning and have just rolled out. Got a fair bit done as well and so far everything is going just fine.
I have the front panel back from the powder coaters now and have been out and purchased some Letraset to do the lettering on the front.
I also found a brand new Simpsons meter on EBay in the US to replace the old cracked one.
I also removed the horrid looking white plastic main inlet box that was bolted to the back and replaced it with a nice piece of Stainless and a big cable gland to neatly house the exiting mains cable.
I have also neatened up the cable from the connection rails at the back of the PSU case that go to the umbilical lead socket again on the rear. It all looks SO much neater
I now just have the heatsink to fit, the front panel to finish and wire back in and then the top and bottom plates to drill and bolt on and it should then be ready for the test switch on (with a large pole )

[p1t8ull]

Jim, you are the undisputed king of pimpness

[Carl B]

That PSU is looking awsome there Jim.
With them new caps fitted and the wiring so neat I don't think you have anything to worry about going pop, fizzel or bang.

Carl