AVO VCM 163 Meters

[Tony DF]

While not about the meters, I didn't want to start a new thread regarding the VCM 163
I have not seen anyone mention cleaning up the rust on the handle bolt heads that always seem to be rusted on these testers. As you know they are pinned and difficult to remove. What I did was get a piece of thin wall Brass tubing available at hobby shops.
Over here (North America) K & S Engineering out of Chicago, Illinois makes an 11/32" x .014 thin wall brass tube. (8.73 mm x .355 mm).
I chucked it up in the lathe and cut off a ring sized piece about 1/4" long. After you remove the burrs, it is the perfect size to slip over the bolt heads. It will stay in place by itself.
You will have to tilt the tester (blanket ?) to keep the bolt heads pointed up. Doing one at a time, using a q-tip dabbed in naval jelly (rust remover). You can submerge the bolt head in product and the brass "ring" will form a dam around the bolt head while the naval jelly works it's magic. I think I let it sit on each bolt head about half an hour.
Using paper towels to absorb the naval jelly and a clean rag for final wipe down. The dam formed by the brass ring will prevent the naval jelly from attacking the soft aluminum (anodized) handles (causing discolouration). The added chemical properties of the naval jelly is, it contains an additive to prevent further rusting of the unprotected metal bolt heads.
Now my tester looks great. While not the look of stainless steel, at least the rust is gone. The rusted bolt heads always bugged me.
Thank-You for this thread guys (about meters). I am learning a lot.
Tony
https://ksmetals.com/products/br014-...546caef3&_ss=r

[MotorBikeLes]

Bazz, I once intended to do some silver plating. On what? Off topic.
Anyway, I bought a decent quantity of sodium cyanide, then decided not to plate the part after all. I still have that unopened NaCN container in side an outer plastic Tupperware container. Goodness me, just a fraction over 60 years ago. Tempus fugit.
Les.

[waran2005]

Thanks Tony, great advice about the rust removal process for the handle machine screw, I will look into getting that done. I also didn't realise that they are pinned in place, I tried to remove one and gave up thinking it must be seized, so decided not to pursue any further.

Well, I have made some more progress to my VCM, I fitted the new op amp board, replaced most of the electrolytic capacitors, although I have one left to do on the power board.

Refurbished knobs fitted, valve panel refitted. It all works really nicely, but I've not progressed with the calibration as there is still a discrepancy of 1.5 mA on the 30 mA range, 100 and 10 mA read equally, so something is not quite right, further investigation required, although I have checked those resistors once already.

So it is working, oh, and the B9A valve socket needs replacing, not a major issue as I can use the adaptor I refurbished the other day that came with it, a sort of mini side project.

Anyone have any idea regarding the discrepancy for the 30 mA range, apart from the shunt resistor?

[waran2005]

Some more photos of the discrepancies on the current ranges.

[waran2005]

And some more...

[Bazz4CQJ]

Impressive progress Waran! Cannot help you on the Ia meter issue; that is one part of my 163 which has always been well-behaved, so never had to delve in to that circuitry.

B

[Longespee]

Waran, have you checked R21/20 2.2M resistors out of circuit?, they look like the original Welwyn and do drift making calibration difficult, from memory I think they are 1%.

On another component note, I had real problem ( until I found it was the culprit ) with C8 the turquise Hunts @ .015uf, Hunts should have been enough of a warning but I missed it, anyway it was intermittent and once removed the leg fell out of the cap, a common fault with these externally soldered versions apparently.

[waran2005]

Thanks Bazz, I have limited time and like to get as much done as I can.

Thanks for the advice Longespee, I have checked the 2.2M resistors out of circuit and they are within tolerance, but only just! I will replace them anyway if they're that problematic, it's soumd advice and I should have done it anyway.

C8 may well be original and I've not replaced it, again, I think I will if it is likely to be an issue.

No pinched wires though when I removed the bottom cover, so that's some good news and all switches and soldered joints appear fine.

Where do you stop when replacing components, I understand to make it 100% reliable / as good as new then it's probably the best option. I just don't have the time or resources to complete a task like that, so what's considered absolutely essential?

Even replacing the electrolytics made me paranoid, not that I'm not confident in my abilities, it's just that they were working well before removal, and the boards are old and I know they don't generally respond well to a soldering iron. I was worried about causing damage to them, maybe introducing problems they didn't originally have etc. Thank god for the solder removal gun / work station, that worked well and made easy work of it, causing virtually no damage. I did notice though that the Thermister must have been replaced at some point as the board is damaged in that area!

[Bazz4CQJ]

Originally Posted by waran2005

Where do you stop when replacing components, I understand to make it 100% reliable / as good as new then it's probably the best option. I just don't have the time or resources to complete a task like that, so what's considered absolutely essential?

Even replacing the electrolytics made me paranoid, not that I'm not confident in my abilities, it's just that they were working well before removal, and the boards are old and I know they don't generally respond well to a soldering iron. I was worried about causing damage to them, maybe introducing problems they didn't originally have etc.

What you are talking about is why I decided to build an entirely new oscillator. As you say, even the original PCB's are iffy and the copper tracks start lifting.

Stick with it; I'm certainly very impressed by the approach you have taken with the meters (so much so that you know what I did), the pics of the finished items and the op-amp boards all of which look very competently done indeed. The 163 is worth it! You've made a load of progress; you make me feel really bad - but that's my problem .

PM'd also

B

[Longespee]

Indeed the electrolytics on the osc and amp boards gave me the same feeling as all were fine and tested good ( I had so many probelms I can't remember exactly which it was), that said I replaced many of them only to find that they hadn't helped my problem, next to go were the transistors which still didn't help, I eventually found my bad cap was C2 1990pf on the amp board, rightly happy but frustrated I put the transistors back, I really wanted to put the electrolytics back!!! but didn't, I lifted many of the board resistors too all were perfect.

C8 I would definitely as it's a Hunt's, I think I put a Mustard in there.

I did find rotary contact on S4 was a problem and the wafer was riding under it because of a broken phenolic, that was a job lol. The more I think back this machine has been a big pain, but it ( when working ) does such a great job.

[Bazz4CQJ]

Originally Posted by Longespee

, I eventually found my bad cap was C2 1990pf on the amp board,

That's interesting. Those Sufflex polystyrene caps were not bad components, but certainly on the Osc board, they were left "flapping around" with unusually long leads on them, and that was not good for a Sufflex. Of course they are negative tempco; did you replace with similar item?

On my all-new Osc board, I extended the copper tracks to the Sufflexes so they have much shorter leads.
B

[Longespee]

Good point Bazz, I need to check although I think I did, but I seem to remember a Lemco mica going in one of the boards.
Yes a good idea on the lead length, some thing that ****** C8 Hunt's needed hanging around on a moving switch.