MCI 500 CV control going crazy on one I/o module HELP

roginator · 14th June 2008, 12:17 PM

whell I have a problematic CV on I/O channel
actually when turning on desk..i/o cv seems to work OK, but after 2 hours ..cv goes crazy...and range is smaller after 3 hours it goes to distorsion in all range of fader same level

tried another VCA , same thing, and another...again same thing

replaced transistor in that area and
tl080

but still nothing
actually from fader I have signal and its all the time OK but after 100K reesistor on input of tlo80 pin 2 evrything goes wrong...

same effect when using VCA busses 1-8 so problem is in fader ACN buffer around TL080

anybody any idea...

HELP!!!!

The Tick · 14th June 2008, 03:58 PM

MCI 500 CV control going crazy on one I/o module HELP
whell I have a problematic CV on I/O channel

actually when turning on desk..i/o cv seems to work OK, but after 2 hours ..cv goes crazy...and range is smaller after 3 hours it goes to distorsion in all range of fader same level

Are the faders going full or high gain ?.

It is a while since I've had to work on one of those boards, but is there a Vca master ?
Is the gain on various channels totally random, or are they all going up in gain and you are unable to shit them off completely ?

Commonly with these consoles, and 600's was erratic 5V rail that is used as the VCa control. That drops console goes very loud.

tried another VCA , same thing, and another...again same thing

replaced transistor in that area and
tl080

but still nothing
actually from fader I have signal and its all the time OK but after 100K reesistor on input of tlo80 pin 2 evrything goes wrong...

same effect when using VCA busses 1-8 so problem is in fader ACN buffer around TL080

anybody any idea...

HELP!!!!

roginator · 14th June 2008, 04:24 PM

HI

Thanx and sorry if I pointed error wrong
ACTUALLY its only on one channel (31)

and when I switch on console everything worx ok

but after 2 hours CV range wich should control VCA is smaller and smaller
at the ends ALL fader range is IN max level and has distorsion

what component needs 2 hours to go tollaly wrong....????????????

Velvetfreddy · 20th June 2008, 05:20 PM

I highly recommend that you contact Steve Sadler at Blevins Audio. Even if you are adept at audio electronics, he will save you some serious time finding the problem. He has a telephone service subscription that is a steal of a deal.
mcijh@aol.com

amorris · 20th June 2008, 08:44 PM

have you tried replacing that 100k resistor? resistors go out of tolerance especially after they warm up, Id expect it to be carrying significant current to make it heat up though. but it could be something to try.

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14th June 2008, 12:17 PM	#1
roginator Gear maniac Join Date: Dec 2005 Posts: 279	MCI 500 CV control going crazy on one I/o module HELP whell I have a problematic CV on I/O channel actually when turning on desk..i/o cv seems to work OK, but after 2 hours ..cv goes crazy...and range is smaller after 3 hours it goes to distorsion in all range of fader same level tried another VCA , same thing, and another...again same thing replaced transistor in that area and tl080 but still nothing actually from fader I have signal and its all the time OK but after 100K reesistor on input of tlo80 pin 2 evrything goes wrong... same effect when using VCA busses 1-8 so problem is in fader ACN buffer around TL080 anybody any idea... HELP!!!!

14th June 2008, 03:58 PM	#2
The Tick Gear interested Join Date: Jun 2008 Posts: 1	MCI 500 CV control going crazy MCI 500 CV control going crazy on one I/o module HELP whell I have a problematic CV on I/O channel actually when turning on desk..i/o cv seems to work OK, but after 2 hours ..cv goes crazy...and range is smaller after 3 hours it goes to distorsion in all range of fader same level Are the faders going full or high gain ?. It is a while since I've had to work on one of those boards, but is there a Vca master ? Is the gain on various channels totally random, or are they all going up in gain and you are unable to shit them off completely ? Commonly with these consoles, and 600's was erratic 5V rail that is used as the VCa control. That drops console goes very loud. tried another VCA , same thing, and another...again same thing replaced transistor in that area and tl080 but still nothing actually from fader I have signal and its all the time OK but after 100K reesistor on input of tlo80 pin 2 evrything goes wrong... same effect when using VCA busses 1-8 so problem is in fader ACN buffer around TL080 anybody any idea... HELP!!!!

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14th June 2008, 04:24 PM	#3
roginator Gear maniac Join Date: Dec 2005 Posts: 279	HI Thanx and sorry if I pointed error wrong ACTUALLY its only on one channel (31) and when I switch on console everything worx ok but after 2 hours CV range wich should control VCA is smaller and smaller at the ends ALL fader range is IN max level and has distorsion what component needs 2 hours to go tollaly wrong....????????????

20th June 2008, 05:20 PM	#4
Velvetfreddy Gear nut Join Date: Jan 2005 Location: Nashville Posts: 131	I highly recommend that you contact Steve Sadler at Blevins Audio. Even if you are adept at audio electronics, he will save you some serious time finding the problem. He has a telephone service subscription that is a steal of a deal. mcijh@aol.com

20th June 2008, 08:44 PM	#5
amorris Gear maniac Join Date: Oct 2004 Location: winter park Posts: 190	have you tried replacing that 100k resistor? resistors go out of tolerance especially after they warm up, Id expect it to be carrying significant current to make it heat up though. but it could be something to try.