4032E Build

[waltzingbear]

what year is on the lower board?

[amillar]

Hi Anthony,
Just seen the FB link to this - as the designer of the "coathanger mod" let me know if there's any questions I might be able to answer! Long time ago but it comes back to me in the end 
Cheers,
AndyM (there are two Andy's being referred to here, so just to prevent confusion!)

[horizonsound]

I have three of them, and my assumption is they are 1979(?)
There is no date, but the code is CF82E19A779 on each of them.

[horizonsound]

Hi Andy,

I sent you a personal message, but hoping you can assist here and get me out of this hole!

Anthony.

Hi Anthony,
Just seen the FB link to this - as the designer of the "coathanger mod" let me know if there's any questions I might be able to answer! Long time ago but it comes back to me in the end 
Cheers,
AndyM (there are two Andy's being referred to here, so just to prevent confusion!)

[amillar]

Very very quick reply over lunch break, having skimmed through the above: don't worry too much about pin 8 for the moment. Whether it's connected to 0V somewhere, or to the "post 1986" resistors on the backplane or on the 611 (can't remember which at the moment?), or even if it's completely disconnected the main mix bus will still work.

With the '26 cards in you won't see any signal on pins 5&6, the mix amp action takes this to a "virtual earth". The question is whether you see a signal on pin 10, the mix amp output.

This is going to turn out to be something really simple - there's not much can go wrong here!

I'll try to find time to read through this in more detail later, and we'll keep in contact on PM.

Cheers,

Andy

[horizonsound]

Nothing coming out of pin 10 either!

I ran a signal through a module, routed it to the quad bus, and had it show up perfectly on the input pin 5/6, when the 26 card was removed. Same as my test via the echo returns.
As soon as the card is inserted, nothing seems to get past the summing amp of the 26 card.
I know from the pre VCA insert point it is ok, so it must be in the front end summing.

Anthony.

[horizonsound]

Some wins, still some problems.

I investigated this coat hanger mod, and mix bus - mod. The coat hanger is a a wire that effectively takes to 0v ground off the mix bus - on pin 10 of your module lower edge connector, and re-routes it to pin 78 of the lower edge connector. The trace is then cut, so the mix bus - is independent of 0v ground.

There is also the "pseduo" balancing of the quad bus (?) by adding four vertical resistors on pins 69, 71, 73 and 76 of the upper edge connector, and cutting the ground trace by drilling out the pad on the underside.

By reversing this, I was able to get the modules to function correctly. However, I still have the summing issue on the 26 card, so to work around this, I can route all channels to 31-32 mix bus, then patch the group out to the pre VCA insert return. Ugly work around for now, but at least I can start to trouble shoot other areas.

Coathanger wire cut at pin 10 and routed to pin 78


Coathanger wire start, near "Ready Tape" switch.


Coathanger at pin 78


Coathanger at pin 10 & trace cut.


Pseudo balancing resistors


Traces cut at pseudo balancing resistors on underside

[waltzingbear]

there is no pseudo about it, it when implemented it is a balanced connection.  What it is not is a symmetrical signal. But it is balanced and has all the attributes of a balanced line.

[horizonsound]

Sorry, it was a terminology used by someone with far more experience than I.
If these are related to the quad bus, there would have to be a mod somewhere to bring them over to S5E, as currently they head down S4E. The quad bus + is on S5E. I would suspect the mod would be in the 651, but i checked mine and that is not the case. They still head to the cue send cards.

[waltzingbear]

Have you checked the voltages on card 26, it should be showing you something right now even if it is noisy or distorted.

[horizonsound]

Yep. +/- 18v on the main rails and +/- 15v for the VCA. Both within 0.05v.
I had to replace the regs on the 27 card that produce the +/-15v as they were out by 0.5 - 0.8v.

[brewery]

wow, looks like you have relays mounted next to the aux switches! never seen that before - was this stock? (and what for?)

[amillar]

I don't remember ever seeing relays like that! (Mind you there have been times in the past when I've said things like that and it turned out I designed them  ) Is that an 8k thing perhaps? (I wasn't involved in the 8k design.)

I really need to look at that quad bus wiring - it's annoying that after I did the balanced mod I didn't update the SxE wiring descriptions in the manual to record which ground went where in the ribbons.

I'm baffled as to why those mix amps don't work, it's very strange that all 4 are dead. Are you certain that the patchbay wiring isn't short circuiting pin 10 (insert send) to ground?

On a desk this small you don't really need the coathanger unless you have a very noisy studio so I doubt if your changes will have done much harm, but watch this space...

Cheers,

Andy

[amillar]

Hi,

If you can 'scope the signal on pin 5 with the 26 card out then there's nothing wrong with the channel strip.

What I'd do next is (assuming you don't have an extender for the 26 card) is to solder a piece of wire to the '26 card to T1 pin 6 (actually best to solder it to the end of R50 or R58 which connects to T1 pin 6) then you can attach this wire to the scope with the 26 card plugged in.

If there's a signal here but there still isn't one on pin 10 then I'll bet the patchbay wiring is shorting pin 10 to ground.

As I said before really don't worry about the grounds for the moment. If you want to be sure you could link the '26 card pin 8 to 0V (pins 53,54,55) for the moment while you're testing.

Good luck,

Andy

[horizonsound]

Thanks Andy,

The console is being moved today, so I'll check that out tonight.
Everything does point to a short to ground on the patch bay (already done that once during this build  ), but I've checked everything and it seems ok.
Will do a thorough check once it's back together tonight.