NEED HELP! URGENT! Erratic behavior of 651 centre section

[marcmozart]

Hey guys,
since yesterday I'm getting some strange behavior from my centre section.

I've been running my console from 1 power supply for a few weeks, powering not more than 32 or 40 buckets.

For the last few days I powered only the centre section as all I needed was to listen to some external 2 track.

At one point the centre section started following behavior:
- no sound at all on Monitor
- Mono LED comes on when pressing DIM
- DIM button mutes external to studio source completely

Thats with a maximum of two buckets of channels powered.

As soon as I switch on 3 or 4 buckets of channel, there is no sound coming out of the monitors.

My first thought was "aligning power supply"...

Any ideas?

Really appreciate your input...

Best,
Marc

[sintech]

Sounds like you have problems with the 24 card in your centre section.

Most likely a logic IC, will have a look at the drawings now.

[marcmozart]

Thank you so much Andy!

More observations:

Tried both powersupplies, seperately and together. Behavior is always the same.

Centre Section works fine as long as no channel buckets are powered. Becomes erratic once I switch on one bucket and more problems when I power more than 3 buckets. (sound cutting off from external to monitor).

[marcmozart]

The following switches are definitely affected and involved in the error:

FILM
STEREO (or QUAD on some consoles)
MONO
(LED for STEREO doesn't go off if I switch in film mode)
DIM

[marcmozart]

My tech Gil Martini send me a quick e-mail (from Brasil...)

He thinks it could be a bad switch for the Centre Section under the patch.

Here's what he wrote "If you have a bad connection thru the small power switches under patch, that means voltage is ok untill you drift
Current to drive status lines to console buckets.
Usely itīs on logic +11v rail that problem appears, no other way than measure on center pcb"

So I guess I have to buy a voltage-meter, measure the voltage on the PCB and try to swap the switch...

Thoughts?

[sintech]

I still feel this is a card fault in 651, rather than a switch.. but you never know. Really you would need to buzz through the 11v rail to each bucket to find that for sure.

Maybe leaving the buckets dark and the 651 on has loaded down the 11v rail and caused some damage to the Cmos IC's

[marcmozart]

I still feel this is a card fault in 651, rather than a switch.. but you never know. Really you would need to buzz through the 11v rail to each bucket to find that for sure.

Maybe leaving the buckets dark and the 651 on has loaded down the 11v rail and caused some damage to the Cmos IC's

Sounds right - I looked at the switch but it looks and feels solid.

So do you think I should replace some ICs on the 024 card?

EDIT: I take if I find the following types of CMOS ICs I can swap them:
4042
4011
4069
4013
4071
I found them online, they seem very common - any thing I need to specifically look at when ordering these?

[sintech]

Hi, It's all standard stuff, as long as it has the block of four numbers it'll work (don't worry about odd letters after)

As you know eBay is really good for Cmos IC's :-)

[marcmozart]

I don't know anything ;-)

Cool, your help is legendary as always!

Hi, It's all standard stuff, as long as it has the block of four numbers it'll work (don't worry about odd letters after)

As you know eBay is really good for Cmos IC's :-)

[marcmozart]

While I'm running out to buy a Multimeter...

can you guys point me to where to measure the voltage at the centre section PCB?

Thanks!
Marc

[kilmister]

Voltage rails are clearly marked on 651 morherboards backside. Just remember to measure logic voltage between +11V and +18V rails.

-Paavo

[marcmozart]

Thanks Paavo,

indeed too easy... the voltages all look great except between +48 and 0 which is only about 40V

between +11V and +18V rails
reads -7.5V (centre + 2 buckets run from 1 power supply)
reads -6.42V (centre + 6 buckets run from 1 power supply)
reads -7.18V (centre + 2 buckets run from 2 power supplies)
reads -6.51 (centre + 6 buckets run from 2 power supplies)

all others (+18, -18, +11 against 0V) are always within +-0.6V)

I take this as a sign that the voltages are NOT the problem and I should indeed proceed with replacing MOS ICs on the 024 card?

Voltage rails are clearly marked on 651 morherboards backside. Just remember to measure logic voltage between +11V and +18V rails.

-Paavo

[marcmozart]

My tech says (via e-mail):

"Only signal running fron 274 card (film version of 24 card) is the stereo/ film format bus to switch the staus on each channel
May be have a look on voltage resistors  on 274 card or possibly one channel is drifting too much current from the transistor sending the status over all bays"

Of course that doesn't tell me too much. Where are the Voltage Resistors and how do I replace them?

[marcmozart]

Posting pictures of my 024 centre section card...

the backside looks pretty modified - is that due to the film panning?

I'm lost - should have done a mix today. 

[marcmozart]

Patching the mix-bus directly into speakers (using master-fade as monitor level).

Mix-Bus is fine, only problem is that console is stuck in film-mode which is a big problem (means that everything panned to center comes out the Center Channel). Unfortunately no solution.