Hi All, Thought I would describe how I have repaired two of my clock modules on my Ferguson 3V22's
Faulty Clock Display
The display unclips from the front of the machine and one plug to be removed then dismantle the case. You will be left two PCB's one with the clock electronics the other the display. You will first need to de-solder the multiple 150 ohm resistor array to separate the boards the carefully leaver the external LED cover, purple, and the led cover, white, usually forces the plastic through the board some may brake off but doesn't matter as you will put these back with a small amount of glue.
LED Cover Removed
Resistor Array Removed
You will now be left with just the faulty LED board
You will now need some Acetone to dissolve the glue over the LED's. I used Oily Nail Polish Remover but be aware that some of these products are Acetone free. I used a shallow plastic tray with just enough Acetone to cover the LED side of the board.
Leave this soaking for a few hours then lightly scrub with an old tooth brush. It will take two or three goes to get all the glue off. You will be left with microscopic LED's on the board that look to be "spot" welded to the copper track but these will come off by applying a small amount of pressure with a small screwdriver. You will be then left with a bare copper board. You will need to tin the copper ready for mounting the new LED's.
Next you will now need to mount the new LED's. I found the best to use where 0603 surface mount devices (red). 0402 are two small 0603's where correct with the correct height to mate with the display and sit across the connection tracks correctly . For those that don't know 0603 is the SMD (surface mount device) size. Very small to solder but doable. MAKE SURE you solder the LED's in the correct way around with the CORRECT POLARITY!! I used my Fluke meter to check on diode test as it just about illuminates them.
The new LEDs do not require anything like the same drive for the same brightness so you will have to replace the resistor array with individual resistors. I found 4.7k or 5.6k (preferred). For those in the know do not add resistors to the two common return lines as this will cause the LED's to pulse with the seconds LED. You will need 20 of these resistors.
Glue the display covers back on after testing on your machine. I have done three of these now and its nice to see the machine fully functional again with working clock display.
All to do one mine was finish the r.f. alignment and check the picture, recorded off another aligned machine.
And the picture
Just a note to say I have never come across a duff driver pin on the clock chip when I used to service these in the early 80's
Any questions please ask
Adrian
Fantastic post Adrian ?
A very useful how-to guide, thank you for taking the time to document the process and share it with us. This is worthy of being made a sticky so its not lost, which it now is.
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An Agilent DSO?! Your lad said you had an enviable workshop... it might encourage me to look into the dead segment on my Thurlby bench PSU - annoyingly, the top right one.
@crustytv Hi Crusty, thanks for leaving as a "sticky" I thought it would be useful as nearly all the ones you see have at least one duff segment! In the days of these VTR's the clock units where prohibitively expensive. Never tried to repair them then but with the advent of SMD components I thought lets give it a go. fiddly mounting the leds I rest them on the prepared board then hold with a small screwdriver blade whilst I tack one end then solder the other, wait a minuet then solder the tacked end. If you lose or melt an LED, bin it start with a fresh one as they are pennies.
@cathovisor Hi I bought a Philips PM 3226 (Dual 15Mhz) when I started on my own in 1977 with a PM 2522 digital meter
The scope and meter cost me £618 from the Philips Rep. Had to work hard to pay for that. Decided 2 years ago to update the scope, £14 pounds cheaper, in real terms than the Philips! Used to look at the PM5519 colour test generator in envy as it was £1200. Its sat above the Philips Scope. As the years go by You can obtain the stuff you could only wish for when I was younger. The Agilent, now Keysight was on offer. I use the same at work and like it very much. This one has the 200Mhz option fitted, the one at work is 500Mhz touch screen version. Just a bit of history.
Adrian
I have far too much vintage test kit - I have two of those Philips pattern generators plus the much later fancy ones whose numbers escape me right now and top of the heap is a Tek TSG-271.
My first decent scope was a Hitachi V-222 and I still have it but again, I have many others - the analogue range-topper here is a Tek 2445B and the digital DSO is a Teledyne LeCroy 200MHz job.
I need to have a prune.
It's quite an eye-opener as to just how much more efficient up-to-date LEDs are compared to their predecessors- the received wisdom of 40 years ago was 20mA for acceptable brightness, now a tenth of that is plenty with many.
Recently found my NOS stash of 1980`s LED`s and was surprised how many were very diminished in output, the boring 5mm red and green colours.
I imagined their life was estimated under working conditions, but perhaps not.
