Author Topic: VU meter not responding to VCA ---SOLVED---  (Read 3731 times)

oyanliz

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VU meter not responding to VCA ---SOLVED---
« on: May 02, 2020, 08:17:59 AM »
Hi

I have some VU meters not responding to VCA fader voltage. I swapp the 10 pin ribbon cable (S23E) coming from a channel to another VU meter and works fine, so I supose that the issue is not in the channel or in the ribbon cable. In the VU schematics are TL072 op amps (see attached pdf)... but I supose that my VU meters are an old model, as they only have 6 diodes and a resistor. I check all diodes and seems that they are ok. Should I replace 3v3 diodes? Or is there something that I am missing?

Any help will be welcome.

Thanks in advance.

Regards.

Oihan
« Last Edit: September 28, 2020, 01:14:13 PM by oyanliz »

horizonsound

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Re: VU meter not responding to VCA
« Reply #1 on: May 02, 2020, 08:31:51 AM »
Hi Oihan,

Your VU meters should be fine. Assuming each channel responds correctly to audio signal, but not VCA, then....

I would suggest checking that not just the logic card is OK (212 transistors), but the 112 FET on the group amp card (RG12). This is where the signal is switched to the VU meter.
Note that if you have changed out 212 transistors, some more common variations have different pinouts on them.
Also ensure the edge connectors are cleaned with deoxit. Sometimes a slight wiggle of the card can either make or break contacts here.

Anthony.

oyanliz

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Re: VU meter not responding to VCA
« Reply #2 on: May 03, 2020, 11:12:25 AM »
Hi Anthony,

The question is that when I plug the S23E cable coming from a well functioning channel, the VU meters are not working fine. For example, the VU meter of the channel 23 is not responding to "VCA to monitor" (VU meter status changes fine), and VU meter of channel 24 is responing to "VCA to monitor". So I unplug the S23E connector from VU meter 23 and connect to VU meter 24, then VU meter 23 (connected to a 24 channel strip) does not work and VU meter 24 (connected to channel strip 23) works fine. So I asume that the issue it is not on the channel strip. I have replaced some transistors in other group cards RG10, 11 and 12, but I think this is not the issue here. Anyway, please insist if I am missunderstunding your replay.

Thank for your help.

Regards.

Oihan

oyanliz

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Re: VU meter not responding to VCA
« Reply #3 on: May 10, 2020, 10:07:37 PM »
I have been testing all the VU meters swapping the S23E ribbon cables and I have 4 VU meters not responding to the fader voltage when VCA to meter mode is activated. I plug the S23E ribbon cable from a well working channel (from working VU meter) and neither of those 4 VU meters respond to the fader.

I have attached a photo of the VU meters of my console. It seems that all the diodes and resistor are fine... does someone know something about a similar issue?

Thanks in advance.

Best regards.

Oihan

oyanliz

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Re: VU meter not responding to VCA
« Reply #4 on: June 03, 2020, 07:47:06 PM »
Hi all,

I have moved the non working VU meters (4 in total) to the last 4 VU meter panel. I do not know why, but now only the last two are not working. So swapping between them... 2 get fixed...

I will leave them as is for the moment, I think it is not a good idea to start replacing components as diodes, resistor...

Regards.

Oihan

radardoug2

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Re: VU meter not responding to VCA
« Reply #5 on: June 03, 2020, 11:47:56 PM »
I've had problems with the bolts going into the meter getting loose, and losing contact. You have to take off the electronics card, and retighten the meter bolts, and then re-assemble. Bit of a pain. Thats why two of your meters came back to life!

jimlfixit

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SSL VU/PPM meter M4 bolts and contacts
« Reply #6 on: June 11, 2020, 06:38:43 PM »
As I recall, the VU/PPM Sifam meter bolts were M4 (metric M4 thread). SSL fitted their PCB's on these bolts and one of them was 0V?
SSL used internal shakeproof washers in order to get a bit of a 'bite' with the bolts (to make a contact) under the PCB and soldered them in place but, you could use the EXTERNAL shakeproof washers instead which actually 'bite' more into the brass nuts and washers fitted to the Sifam meters and provides a better contact.
Hope this helps from Jim Lassen.

amillar

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Re: VU meter not responding to VCA
« Reply #7 on: June 16, 2020, 10:32:03 PM »
In the VU schematics are TL072 op amps (see attached pdf)... but I supose that my VU meters are an old model, as they only have 6 diodes and a resistor.

I'm intrigued by this, it does look from the manual as if at some point in the late '80s we changed from the "unbuffered" VU to the "buffered" as standard. I certainly remember designing the "buffered" version, with the deeply cunning* "sort of 0V" connection to pin 2 of the Molex connector so that it could either work as a normal 4k meter or be used in something else - probably something to do with the 5k since it's got both a 4k (SL672) and 5k (SL515) part numbers? I do remember it meaning that customers could have extra meters on the patch bay which wouldn't load the signal.

Anyone got a G series with VUs? Have they got TL072s in?

Cheers, Andy

* Actually it wasn't that cunning, in fact it's a completely pointless connection. But for some reason at the time I felt very pleased with myself about it...
co-designer and project manager G series analogue 1987
channel strip designer J series 1992-93
design "caretaker" 4000/6000 1985-93
analogue team leader ARC/Bertha 1988-92

oyanliz

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VU meter not responding to VCA
« Reply #8 on: September 28, 2020, 01:13:10 PM »
Hi all,

Sorry for the delay, I have been busy with some projects so...
Thank you, Jim and radardoug2! I disassembled and assembled back again the faulty VU meters. They all work fine again.
I have attached some pictures of the VU meter models I have in my console.
Best regards.

Oihan

Timetravel

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Re: VU meter not responding to VCA ---SOLVED---
« Reply #9 on: October 16, 2022, 11:57:33 PM »
Found the same problem on a lot of my meters. Just found this topic here. I took of all the external nuts and washers which are bronze cleaned and sanded them. The final trick was to take out the internal antishake washers as jimlfixit mentioned and install them in the outer side of the pcb.This way the electric contact will not be disrupted by iron washers.
I dont know how SSL made this error placing iron washers between bronze contacts.
of course, i sanded the bronze parts ( even the internal bolt) and it was rock solid again.

amillar

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Re: VU meter not responding to VCA ---SOLVED---
« Reply #10 on: October 18, 2022, 06:09:45 PM »
I dont know how SSL made this error placing iron washers between bronze contacts.

I do. It's because when they were new the steel washers were nicely plated which meant they worked, and we didn't expect people to keep using these desks for 10 years (because we assumed they'd want something more modern by then), let alone 35 years! If only we'd known, we (the engineers) would have been very pleased (the business team would have been less pleased), and would have probably thought about things like this more.

Cheers,

Andy
co-designer and project manager G series analogue 1987
channel strip designer J series 1992-93
design "caretaker" 4000/6000 1985-93
analogue team leader ARC/Bertha 1988-92

Timetravel

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Re: VU meter not responding to VCA ---SOLVED---
« Reply #11 on: October 19, 2022, 03:25:38 AM »
Yeah Andy. I can imagine that. I just thought that its a general rule of electrics : if you have bronze contact, do not put iron in between. Kinda commonsense!
But engineering inside this console, is crasy. Details beyond what someone can think as normal.
Congrats to you and ssl team for this marvel!

amillar

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Re: VU meter not responding to VCA ---SOLVED---
« Reply #12 on: October 19, 2022, 02:28:50 PM »
The other thing about audio equipment in general is that far fewer people are involved in designing them than you could possibly imagine...so very often the people who design it are really, really good at one area of design but much less so than another, but there just isn't the money floating around to get the design thoroughly checked over...one person designs it and off it goes to production! When I left SSL (and the music / broadcast industry) I moved into an industry where every detail has to be got perfect (because people will die if it isn't!) and suddenly costs rocket up a hundred fold at least, it was quite interesting.

We did design one desk, called at different times the ARC or Bertha, where every detail (mechanical and electrical) was actually very carefully worked through and reviewed, that would have been a fantastically reliable desk (as well as amazing sounding). Sadly by the time we got it near production around 1991 there was no market for a £500,000 analogue desk... Bits of the design did make it into the 9000, but that was designed much quicker with a much smaller team.

This is why I like dropping in and out of the ProAudio DIY forum on Facebook, at home you can, if you have the skills and knowledge and know who to ask for advice, nearly always make higher quality equipment than you can buy! Because you have the time to check everything carefully.

That's all got very philosophical from a discussion about VU meters ;D I guess it's because it's my day job now, making sure engineers really have thought about everything that could possible go wrong (even 20-30-50 years into the future) so they don't kill people... At least we didn't have that problem at SSL, short of the desk falling on you! Or sticking your hand into the awful 4000 power supplies. Or grabbing the 263Vdc on the bargraphs...

Cheers,

Andy
co-designer and project manager G series analogue 1987
channel strip designer J series 1992-93
design "caretaker" 4000/6000 1985-93
analogue team leader ARC/Bertha 1988-92

Timetravel

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Re: VU meter not responding to VCA ---SOLVED---
« Reply #13 on: October 25, 2022, 02:15:21 PM »
Hey Andy,
i always read your memories and stories like lullabies of an golden time. Very curios about the Bertha, but unfortunately....
Yes, nowadays, safety and human life is becoming priority number one, but that will never make room for engineering marvels and pioneering courageous designs.
Cheers, and best regards
Erjon