Broken Faders on VideoComp VES-one genlock

[Overmann]

Years ago I was gifted a genlock for use with the Amiga line of computers. It powers on and appear to work, but the faders were falling apart. After years of being on the lookout I managed to find another VES-two (it's actually the VES-one, i misremembered. Thank you timeandfrequency for pointing it out), but sadly its faders were in even worse condition. Recently I've concluded that instead of looking for a third unit I might as well try to repair the two units that I have.

The problem is I have very little knowledge when it comes to faders (and electronics in general). I do have some skill with a soldering iron, but thats about it. I am hoping that someone here, with knowledge on the subject, might be able to help me find a replacement part that i might solder on to the boards, or modify in some way to make them work.

After disassembling one of the faders i found this writing:
A, 035, 10k, Preh, E, S
A, E and S are for the three pins.

I also made this post with pictures of the faders:
https://imgur.com/gallery/odd-unidentifiable-fader-QU0FJBw

Do any of you know if there is a modern replacement for these faders? Any help or suggestion greatly appreciated. I think they are 10k, 70mm length, 50mm travel, linear, but thats not enough for me (as a layman) to find a replacement part.

[timeandfrequency]

Hello Overmann,

Uh, I could not even find a single picture of the Videocomp VES-TWO genlock on Google, I only found some information about the VES ONE.


As far as I understand, PREH is a German manufacturer which now focuses on automotive parts and electronic systems

Now let's find replacemement parts.

Check out this one  (6 units available)
https://www.ebay.de/itm/123873406755
Perhaps ask the seller about the exact size of the part. IMO, they seem a bit too short (perhaps only 35 mm travel, 50 mm full lenght).


Most of the PREH faders I could find are upright models
Those in the VES TWO are of flat shape and are actually lying. But ask Greider if they dont have a few parts that matches your requirement.


Furthermore, the part you describe has a 50 mm travel, and this is unfortunately rather uncommon. Standard travel course are 45 mm and 60 mm.

Also check the other defective fader if they are exactely the same as the one you already dessoldered.

Do you want only a genuine replacement part ? Or would a functional replacement suit too ? In the latter case, adapating another fader having similar mechanical size would certainly be possible and do the job.

If a functional replacement is acceptable, the important features are :
- the fader height
- the fader resitive law   As nothing is indicated on your fader, I would assume it is 'A' (linear), but this has to be verified
- the fader total lenght (because too long might be a problem if other parts are located in vicinity.
- the fader mechanical travel distance, but it's possible to cheat : 45 mm might do it, and 60 mm too, but in this case, it needs other cobblings to work properly  (I we need too go that way, i'll be more specific in a later post)

What is NOT important :
- the fader total resistance value : as far as what you need is an 'A' law, the actual resistance value of the replacement part can be equal or above 10 k (because it's always possible to add a parallel fixed resistor so that it behaves as a 10 k fader)
- the actual position of the pins (electrical connexions to the resistive track or the mecanical positioning pins), because it's always possible to drill new holes in the PCB and glue the fader at its' adequate position
- mono or stereo fader : if you catch a stereo fader, just use one side.


Some interesting parts that might be an acceptable replacement :
10 k (unknown law) 45 mm https://www.amazon.fr/lin%C3%A9airement-Potentiom%C3%A8tre-coulissant-coulissante-potentiom%C3%A8tre/dp/B07D42SYPH
10 k A  75 mm total lenght https://fr.aliexpress.com/item/32990553553.html
10 k  A  60 mm travel https://sinolec.co.uk/en/slide-potentiometers/1211634-10k-ohm-slide-linear-slide-potentiometer-fader-with-dust-cover.html

[Overmann]

This is very helpful, thank you timeandfrequency. You are correct in that this is the VES-one. I misremembered. Even the VES-one is pretty obscure, but it was in use as the center piece of the film-department of the school I went to back then. They had it in storage since the 90s, but it was in pretty rough shape. I suspect these faders just disintegrate with age.
I don't mind a modern replacement at all. These faders do not appear to be of particularly high quality so If there is a modern, high quality replacement that I can use or modify to do the job then that would probably be the best way to go. I tried calling mouser for help finding a replacement, but they were only able to help if I was a corporate costumer making a bulk order. But I was able to find some that look like they might work, and one of those might the be same as the Alps you linked to in your post?
https://no.mouser.com/ProductDetail/Alps-Alpine/RS45111A6A08?qs=m0BA540hBPd3sxZzJ%252BQ35g%3D%3D

You think this might work, with some modifications? I also had these:
https://no.mouser.com/ProductDetail/Alpha-Taiwan/RA4520F-10-20D1-B10K?qs=pp9WcCiiSR%252Bg%2F%252B8%252BL1mM0A%3D%3D
https://no.mouser.com/ProductDetail/BI-Technologies-TT-Electronics/PS45G-C1SBR10KN?qs=XKNj3RTD%252B%252B89yqUQNM%252B6rw%3D%3D

Id much rather buy new parts then NOS or used.

[timeandfrequency]

Hello Overmann,

Alps-Alpine is top-notch brand so it is probably the best choice. Alpha is OK too for your application.  'TT' is part of BI (Beckmann Industrial), which is also a renowed brand. Actually, the quality of the fader is not that important as it would be in an analog audio mixer : no video signal goes through the fader. The latter probably just provides a variable DC voltage to the actual video mixer assembly.

As far as the parts you choose fit mecanically into the existing enclosure (check on the mecanical drawing for actual part dimension), you're on the safe side. Then you order the 10 k 'A' value part.
I cannot give you any answer about the fact that a particular part will mecanically suit or not, because I don't know the height of the genuine part.

What surprises me about the Mouser's page regarding the RS45111A6A08 part is that the description says 'Slide Potentiometers 10K OHM "B" TAPER' which speaks for a log law, and below the 'Taper' feature is mentionned as 'linear'. It's worth calling/emailing their customer service for an explanation.

By the way, could you confirm that the genuine faders you need to replace are of 'A' law ? A basic measurment with a multimeter will tell you the truth.

[Overmann]

I tried, and found that my multimeter must have broken since last time I used it. I must get a new one. But 'A' law signifies a linear taper? It must be linear if it's meants to smoothly transition from one video source to another, I think. But I'll put a new multimeter on the shopping list and check it out. It says B taper, but the  documentation also describes it as linear. I'll also measure their height while I'm at it. It'll be great to finally replace these faders. If I'm lucky I'll have TWO working units and can have a go at some 90's video production

Do you have some suggestion regarding how to identify which pins should be soldered to the PCB? The faders I'm replacing have three pins but some of the ones on mouser have more then that. Which are the important ones ?

[timeandfrequency]

Hello Overmann,

I tried, and found that my multimeter must have broken since last time I used it. I must get a new one. But 'A' law signifies a linear taper?

Well, I just discovered that the travel law marking depends on the country of which the pot is sourced from .
In Europe, linear law is marked 'A'. And that's what I worte above. But in Asia (like the Alps parts), a linear law pot is marked 'B' 

Using a multimeter would certainly help to figure out which part best suits to replace the defective fader. If you need a new one, try to avoid buying the cheapest crap. As Dave explains, Fluke manufactures the most thrustworthy

]

... multimeters in the world. They last for decades in case of private use, but this comes at a price. Yoy may have a look to Brymen TE or this one specced and sold by Dave, which is a bit more affordable.

Do you have some suggestion regarding how to identify which pins should be soldered to the PCB? The faders I'm replacing have three pins but some of the ones on mouser have more then that. Which are the important ones ?

Pro faders have electrical pins that connect to the resistive surface and the wiper and also mechanical pins that are used to attach the part to the board. Those avoid putting mechanical stress on the electrical pins while moving the wiper.
Concerning the RS45111A6A08 part, the datasheet gives some clues.
The drilling plan on page 9 shows markins '1', '2' and '3' on the last drawing.
And the vertical scale explanation on the chart at page 3 helps to identify where each pin is connected.
Pins 1 and 3 are the ends of the resistive surface. For the chart provided, Pin 1 is connected to GND (= voltage measurement reference level).
Pin 2 is the wiper connexion.

[Overmann]

Thank you again! That's a lot of great info on multimeters. I'll have to try to borrow one initially. There are very few brands available for purchase here in norway. There is Uni-T (which is the unit that I had that suddenly stopped working), and there is Fluke, which frankly is way out of my price range. I might look to see if I can find another, slightly higher end, Uni-T, but I can't afford to buy a fluke locally. If not I'll ask around and see if I can borrow something from someone to do the testing on these Videocomp units. At least a have a good soldering iron
I dug my two videocomp units out from under the stairs just now and one of them IS actually a VES-two, but they look identical. I'll be having a look at the circuit-boards tomorrow.

I measured the height of the old faders at 9mm now, but there is a bit of clearence so I think a 10mm fader would work. Once I get a hold of a multimeter I'll poke around on the board and see if I can identify which pins go where and if there are other things I can learn from the old ones (law etc). In the end I'll try to identify a couple of compatible faders and just order 4 of each of them. Shipping those badboys is more expensive then the faders themselves

[wasedadoc]

A €10 DMM is more than adequate to distinguish linear from log taper.

[Overmann]

I bought a Uni-T UT161D today. I've set the multimeter to resistance and I'm measuring between the bottom pin and one of the upper pins. One of them gives O.L and the other gives a reading of 1.6 kOHM. Sliding the slider does not change the reading. Please note that this slider has completely fallen apart. I've tried to put it back together, but I have to hold it together while holding the probes in place while sliding the slider up and down. It's a bit fiddly, but I assume that if things were working properly I would see a change in resistance as the fader was moving up and down? Perhaps I need to take them out of the cicuit for the measurements to be correct, but I assume that the value would change when moving the slider either way.

I've added some pictures of the boards for the two units. The pot-board is identical for both.

[timeandfrequency]

Hello Overmann,

Thanks for the pictures.


You may evaluate the travel law of you fader even if it is not completely assembled.
On your 3rd picture, left fader : the grey long part is the resistive element. Just mesure the resistance between the bottom metallic surface and each of the five tabs on the right, and report.

[Overmann]

Ok, measurements:

2.7 kO
3.8 kO
3.8 kO
3.7 kO
3.5 kO

This makes no sense to me, but perhaps you can derive some meaning from it 
 

[timeandfrequency]

Hello Overmann,

Indeed, we would expect some kind of progression between the different measurements, which is plainly not the case.
Sum is 17,5 kOhms, which is rather far from 10 k. It's actually closer to the next usual fader value (22 k).
And we even have a decrease in values which means negative resistance. But the latter only exists in some active parts, not passive components like a pot/fader.

What are the potential reasons that can explain the values you mesured :
1. External influence / burden
2. Inadequate measuring protocol
3. Defective test equipement


How to manage these issues :

for 1. As you suggested earlyer, isolating the fader (or what is left from the fader) from the board would certainly avoid rigging the multimeter if that is the cause of the weird values. Desolder the fader before making new measurments is the good way to go on.

for 2. Maybe the lateral grey tabs of the resistive element are of high resistance or are fitted for very specific test protocols. So perhaps it is not the best location to put one of the probes. Keep the 'sliding' probe in the middle of the about 3 mm wide resistive track, where the wipers' fingers actually slide. Do not push to hard to avoid damaging the carbon surface.

for 3. As you just bought a new multimeter to perform these mesurement, and therefore have no track record of its' performance, the trust we have in it is rather low. So considering that it might actually be defective cannot be excluded.


Once the fader desoldered, check the total value by mesuring between the two metallic tabs located at each end of the resistive surface. Something between 9 k and 11 k would be in the awaited span. Try this with different faders. Then redo all of the mesurements by following the 'for 2.' protocol.

[Overmann]

Excellent. I just desoldered the fader and now the readout from the multimeter mages more sense:

3.0.kO
4.4 kO
6.2 kO
8.0 kO
9.0 kO

The min and max I am able to measure when not focusing on the tabs is 80 O and 10.6 kO. The values are drifting a bit, but these readings are approx. what is shown on the multimeter. It looks pretty linear to me. What do you think? Am I safe to order some of the sliders I've bookmarked below?

[timeandfrequency]

Hello Overmann,

Well done ! That looks plainly as a 10 k Ohms linear fader.
You can order the parts you mentionned and proceed with adaptation and replacement.