Chilton CM4 specific info sought

[P.O.]

Hello all,

I inherited a Chilton CM4 mixer from a friend. This mixer has somewhat been modified to work in a broadcast remote situation, and I want to restore it to original 'cause its present functionning is inappropriate for my needs and I also think it's acting weird and it needs to be straightened out.

Now I know you're gonna say there's a manual for the CM2/4 that's easily available, but I have that and it's NOT what I need. I need documentation for the CM4 specifically, because there are differences between the CM2 and the CM4 that are NOT covered in the available PDF. One is the connector that links the master modules: on the CM2 it's 15 pins, and on the CM4 it's 24 pins...

So if you have this kind of information, would you mind sharing?

Thanks! 

 

[Whoops]

I don't remember seeing Chilton documentation shared around these forum.
I would google the hell out of it.

What are the mods the were performed to it?

 

[P.O.]

I could not find other information other that the CM2-4 pdf manual that can be found at numerous places on the internet.

My particular unit had the monitoring module modified to connect with intercom and communication lines used by the CBC. I'm trying to retore it to stock, but it's hard without schematics. There's been a number of XLRs added to the rear panel, a panel with a bank of pushbutton switches added to select comm lines, and an extra pusbutton added to the monitor module...

 

[cyrano]

Many broadcast mixers were small series, built to order. Maybe that's the reason schematics are hard to find?

They might be non-existing, especially as service manuals of that era were made on a typewriter.

Are you sure the mods weren't made in the factory? I've seen some that were pretty ugly...

 

[Whoops]

I think without schematics it will be pretty hard to restore or modify it.
After googling the hell out of it, I would contact all companies associated with Chilton, would contact repair/service techs related to Chilton, past distributors, basically anything related to Chilton and ask to buy the schematics from them.

one thing you can be sure, the schematics exist somewhere on this planet

 

[P.O.]

Well, I worked on the monitor section, trying to restore it to original as much as I could. I'm pleased to say that it sorta works...
Listening with headphones, all channels pass audio (line, I haven't yet tried them with mics) and sound fine. Except the one stereo module I have (M4): audio gets in (I can PFL it) but it does not get out. This likely has to do with the different buss assignation I've seen between the CM2/CM4...
Also, there's a hum on right channel which I believe lives on submaster 2. Talkback mic is inoperative and only delivers hum. Anytime PFL is called it produces a big pop. Nothing comes out of shitbox. Of course there's numerous scratchy pots.

So there's hope: it basically works and none of these things seem unrepairable. That should be a good wintertime project...
I also have to rack them Ward-Beck and Mc Curdy preamps.

 

[Whoops]

Post some photos of the console and also of the work you’re doing

 

[P.O.]

Duh... it's all tucked away 'till the next round of work, and I haven't taken any photos...
Nothing really special, looks like a regular CM4 except module space #1 is unoccupied because of previous mod work and buss board has been cut, and I have one M4 stereo input module at the end of the regular mono inputs, before the M45 stereo output. Meter panel has a clock, the four PPMs, an LED meter for PFL and a shitbox.
I must remember to take photos when I do the WBS and Mc Curdys. Plan to put four of each into two HP 18652A "A/D converter" chassis

 

[P.O.]

What I find very puzzling is that, on the CM3 monitor module, on the buss there is a "DIM" line where the "L" channel normally is... Of course, the L and R buss does not seem to be used on the CM4 (are they?), but if you mix 'n match modules from the CM2/CM4 you could be in for some confusion and surprises... There is a number of different assignation configurations for a given module: I have some M41 modules with 1, 2, 3, 4 and L/R assign switches and three aux sends, and some with 1/2, 3/4 switches. And then the M1 module has NO assignation switches (just CH ON), hard-assigned to groups 1/2 I found out, and three aux sends. The stereo input M4 module has L and R assignation switches (which would explain why its signal on my CM4 goes nowhere), while the stereo input M44 has 1, 2, 3, 4 and L/R switches (which is not much of an improvement). These have only two aux sends.
Bref, this whole line of modules is a mess, and it does take some patience to sort it out...

 

[radardoug]

You know, on a small mixer like that, its not hard to sit down with a peice of paper and a multimeter, and just reverse engineer it yourself.
Then you could post documents here for posterity.

 

[P.O.]

The restoration is going well, all the input modules are working but I'm having big problems decyphering the M43 monitor module. too much differences from the schematic of M3 in the manual. Example: there's a huge hum when I press talkback switch. M3 uses a three-wire electret mic, M43 uses two-wire. Monitoring circuit is very hard to figure out, I have written to chilton for a schematic of M43. Still big confusion around "L" buss used as mute line...
I have ordered capacitors to start recap, I have spotted leaking capacitors (very few) but I started testing and some are bad (dead or high ESR) so I guess I'll go for a complete recap. Problem is original caps are axial type. Axial types are now difficult to find, have very limited choices and are prohibitively expensive. Example: at DigiKey the least expensive axial 68µF is $7!!
The Audiofad faders originally used are now unobtainium and no current fader will fit. Fortunately they are quite simple and easy to repair if there's minor damage.

 

[radardoug]

You dont have to use axial caps. And take the time to draw out your modules schematic. The time you spend will be well worth it.