Avo vcm 163

[vintage_8bit]

Thought I'd I would share my recent acquisition with you all.

I was fortunate to get this tester on approval first, to allow me to check for any major problems. To my delight both meter movements were in good condition and read spot on, when disconected and with 50 uA passing. The only problem with the meters was that with both meters, the perspex covers are a lose fit? The left meter also had an extra washer under one of the scale stand off pillers resulting in the scale not fitting flush to the meter body? This meter had a date of 1978 on it, I assume this is a replacement. I carefully cleaned out the meter cases and fitted in small dessicant packets. There were no signs of corrosion. The tester had fortunately sat unused indoors for several years and with its cover on.

Without performing the cal procedure, which I do intend to do, the left meter read a 1 meg resister spot on. The right meter needle sits on the "Cal" mark as well.

With a new EL84 it appears? to give good results. The only other problem encountered so far is an intermittent circuit selector switch.

[vintage_8bit]

I have now looked at the intermittent switch and I have a mangled contact to deal with. It's beyond reforming, so bit of work here needed. Has any one got the wiring connections for the circuit selector switch? I do have the ammended circuit for the tester and the calibration document, so can manage with this.

[Dekatron]

Can you show a photo of the damaged switch?

Unfortunately I don’t have any more info on the wiring than what is available in the service manual but I have repaired and also replaced a few switches in these testers before so I might be able to answer any questions you have.

/Martin

[vintage_8bit]

Thank you Martin. Well I went for it, I have removed the offending wafer and changed the contact. You can see the before and after pics. The replacement was the nearest I could find and appears to work well. As you can see someone was a bit enthusiastic with the solder. This contact is used in the heater cold possition, so isn't my intermittent fault. Should be back on it tonight.

[Dekatron]

Nice repair!

While you are there you should make sure that the center rotating piece is not splitting up in two pieces as well as making sure that the flat long rotating contact is pressed down properly into the rotating center piece - when these come loose they damage the contacts like what happened with yours. When the rotating contact and the rotating center piece gets loose they snag on the contacts at the edge and destroy them or sometimes instead travel on top of the outer contacts making poor contact.

I've seen this on several VCM163s and sometimes it is easy to repair but sometimes it is more or less imposssible if to much has ben destroyed.

[vintage_8bit]

Thanks for the advice. That particular wafer looked ok. The switch is now assembled but not fixed to front pannel. I will give the rest of the wafers and contacts a close insection before use. I will be looking closely at all the rotary switches, specially after your advice on the split rotating centres. Will report back on progress.

[Dekatron]

There are some photos of a switch that had the problem where the center piece was coming apart and the rotating contact sliding on top of the outer contacts here: https://www.vintage-radio.net/forum/...9&postcount=14

/Martin

[vintage_8bit]

Looked at the photos link, thanks. Have you ever used Servisol Super 10 on the switches? When I've used switch cleaners in the past I then usually use compressed air to remove any excess. I also protect the surrounding area. I know Servìsol is made for this but worry about those plastic centres?

[Dekatron]

I stopped using any cleaning solution after I spoke to people who know more about plastics than me as most agreed that the cleaning solutions would weaken a lot of plastics and being unsure which type of plastic this is I didn't want to risk any more damage.

I usually just look at them how they travel when they are turned and if there is anyone that is wonky I remove it and glue it with araldite and put clamps on it until the glue has set. I also check the rotating contacts to se if they need to be pushed down or the "hooks" (the split metal pieces gripping the plastic) on the reverse side need to be bent to get a better grip.

Just turning the switch back and forth have cleaned the contact points enough to get proper contact back on the ones I've repaired - if they have been to far gone I have replaced the specific contacts.

On a few occassions I've used IPA on a cotton swab or on a piece of paper that I've stuck between the contact fingers that has been making poor contact so I wouldn't drip it all over the place. Quite a tedious job but sometimes well worth the time spent.

/Martin

[vintage_8bit]

No Servisol then. I will use IPA, if required. I have a black wire dropped off from the leakage switch somwhere, so need to sort that before a power up.

[Dekatron]

If you can post a photo of your switch with the loose wire I can compare to one of my VCM163s as I have it opened on my desk for other projects.

/Martin

[vintage_8bit]

That's great, thankyou Martin. I will try and get that done tonight.

[sven_swe]

I had no idea India Pale Ale works well for the switches.

Just kidding, I also use Alcohol for these kind of switches with a q-tip or whatever goes in there. Sometimes these small toothbrush-picks are good.

[Craig Sawyers]

Originally Posted by Dekatron

If you can post a photo of your switch with the loose wire I can compare to one of my VCM163s as I have it opened on my desk for other projects.

/Martin

ONE of your VCM163's?

Craig

[Bazz4CQJ]

Originally Posted by Dekatron

I stopped using any cleaning solution after I spoke to people who know more about plastics than me as most agreed that the cleaning solutions would weaken a lot of plastics and being unsure which type of plastic this is I didn't want to risk any more damage.
/Martin

A problem can arise with some materials, that if you have an existing crack in them, arising from any reason, wetting the crack with just about any low tension fluid can enable the crack to propagate much more easily than if it had stayed dry.

The best example of this is that if you take a glass rod and bend it, it will often take quite a lot of force to break it and then it really goes big time. Take the same rod, scratch it with a glass knife and then wet the scratch (glassblowers will often just lick the scratch), and the rod will then break much more easily and straight across from the scratch. Of course, glass is a brittle material and plastics much less so. However, some old plastics and composite materials may still be susceptible to failure after wetting. Poor old WD40 often gets the blame for causing damage when any other fluid might well have caused the same problem.

B

[Dekatron]

Yes, I have three plus parts for maybe one quarter more.

Originally Posted by Craig Sawyers

ONE of your VCM163's?

Craig

[vintage_8bit]

Didnt know that about the liquid and glass.

One photo shows the closest wafer to the front pannel, of the circuit selctor. The black wire is attached and circled. The terminal is used in the "check hot" possition. (Top of circuit S5A?) Is this 0V?
Other photo is the leakage switch with the other end of the detached black wire and the terminal I think it came from, both arrowed.
I hope it makes sense.

The circuit shows 14 segments. But the circuit selector switch has 8 wafers or 16 segments, what am I missing?

[Dekatron]

Yes, the two black wires are soldered to the same connection in my VCM163, see photo.

[Dekatron]

All of the segments aren't used, some are just used to mount components and others have both sides used in one segment for complicated functions on some switches.

[vintage_8bit]

Thanks for the photo and explanation. Job for tomorrow now.