Decca/Unaohm EP685 TV test generator

[ppppenguin]

Does anyone have the schematics for the Decca/Unaohm EP685 TV test generator? I acquired one recently and while it works there are a couple of problems. I can probably fix them without the manual but it would be a lot easier with it.

This appears to be just the PSU schematic which is the easy bit
https://elektrotanya.com/unaohm-milano_d...nload.html

[ppppenguin]

Thanks to Dave Ingrey the circuit diagram is now in the archive.

http://golbornevintageradio.co.uk/forum/...p?tid=6561

[Desmond]

I too have one of these Colour Bar Generators. Mine is now partially working after repairing the mains transformer.
The leads to the transformer were corroding and the spaghetti sleeving crumbling. fumes from the decomposition process destroyed the fuse holder. The mains switch had gone high resistance and i by-passed it for now.

I could really use the help of the schematic diagram, but it would take me an eon to write fifteen articles.
Maybe the owner of the schematic could e-mail a copy to me?

I have tried to insert some photos of my unit but can not work out how.

Desmond.

[Desmond]

Hello all.
I'm writing to give a follow up to the repair of my newly acquired
Colour Bar Generator, a Unaohm  EP 685A.

After obtaining four pages of the schematic, I figured that I had enough to have a chance of getting it going. My thanks go out to the
Golborne Vintage Radio Forum, being the source of the schematics.

I personally like the look of this piece of test equipment. it is not often that a piece of  test equipment is useful, and looks good too.

Looking at the casings of many of the transistors, I guess that it was built around 1972. I guess a more accurate date of manufacture would have come from reading the date codes on the I.C.'s.

Once I had the schematics I opened up the and removed the two piece case to reveal the internals. Not a good look. The leads to the mains transformer, which were sleeved with spaghetti, had decomposed. It looks like the spaghetti had turned into some sort of acid which had caused the
in-contact extension leads, and enamel wire to corrode and decompose.
The M 205 fuse holder and 200mA fuse also were damaged by the fumes of the decomposing leads.

Round Two: What to Do?
It was far too early to give up and have the pattern generator as a static display only. I am one of  crazy people who still repairs old televisions.
Anyway, it was not going to fix itself, so I took a lot of photos and removed the transformer. So I cut back the old leads and soldered on new leads and used heat-shrink tubing to cover the leads. Next I re-fitted the transformer, connected the leads, plugged in the mains lead, and flicked the lever on the Destruct Switch. Hmm. Dead. Time to break out my multimeter. Mains switch, 70 ohms in the on position. no wonder it did not destruct. I by-passed the switch for the time being. Now I had a pretty little red light on the front panel.






Round Three:Testing.
When in doubt, stop guessing and engage the brain. Nothing from the modulator. Alright I will somehow make room on my workbench for my ancient C.R.O.  and see what is really going on. Bingo, I mean, success. I had some nice waveforms, although erratic, from the Video Out socket.

Spraying contact cleaner into the rear of the ten pattern select switches and working them in and out a number of times fixed up the patterns and also made them stable. While the contact cleaner was close to hand I cleaned the sound modulation switch and the mains on-off switch, by injecting contact cleaner through the opening around the switch lever. This was not successful when it came to cleaning the five switches of the R.F. attenuator. All were open and none responded to cleaning. The corrosive fumes from the spaghetti tubing had worked their way throughout the entire generator. Like a number of things, the switches in the attenuator could not be removed for replacement, so....I bypassed them.

Round Four: More repair work.
I promise, I will get around to cap replacement later, but for now there is still more to be done. EVERY switch contact was suspect. I removed the R.F. out band/frequency selector unit, and cleaned its contacts and band switches. Removing this unit required the use of a screwdriver with a 300mm shaft and the removal of the rear cover.
All the pots needed cleaning as well as the metal to metal contact to the pot's wiper connection.

So how does it work? Quite well. I particularly find the function “test 3” useful. When I get around to posting the photos, you will see that I made a mistake when labelling the R.F. modulator connections. Whenever you look at the modulator and see B5 (Band 5) just realise that ought to read B4.

This looks all nice now, but I am sure when I copy and paste this articleto the website, the formatting will go completely to hell.

Desmond.

[Desmond]

Another update re; my Unaohm EP 658AColour Bar Generator.

Just adding a few loose ends to the repair of my Colour Bar Generator.
I follow many forums, and get the feeling that everyone thinks that the answer to every repair is to replace all the electrolytic capacitors. I replaced just four caps, and only because they were needed, and not because they were there. I also fitted four new screws (six gauge x 10mm) to the case. It does seem to me that whenever  someone takes apart a piece of equipment to repair, their first action is to remove all the screws of the case and throw them over their shoulder.

Although I would dearly love to post photos of the restoration, I do not have much luck posting them. So far, Facebook seem to be the only site with a good up loader.

Other things I'm working on.

One. A Philips PM 5509 G /03 PAL TV Pattern Generator, on which I committed an unforgivable sin. I forgot to take many photos of it before I took it all apart. And yes. I have forgotten where one of the coaxes goes.


Two. A 12” B&W  Portable Television.  Brand name Oscar.
Model P12-H4A9
I only mention this TV because it is so uncommon here in Australia. I once supplied a schematic for the model to a technician friend whom was working on one, and I bought an example of this model recently, only because I knew it used Compactatron valves. so there, in the forty-five years since it was introduced, I've only ever seen and worked on one.
By the way. It does sound odd to say, 12” portable. The fact that it is only 12 inches makes it obvious that it is a portable. 

I did manage to fix it, and will probably submit an article of its repair in the near future.