Midas TR04 console-TR22 com module issues

[mixbus]

Hi All,

I hope you can help. I’m working with a friend on an old Midas TR-04 Theater console from around 1980.

He’s having issues with the TR22 Com module.

PFL isn’t working. It includes the solo, mono, dim, and mute.
Parts of the Oscillator section, including the external out on the front of the desk doesn’t work either.

There seems to have been a mod with multiple resistors done at some point just to the right of the edge connector, that is unhooked on the other end, and that part of the desk isn’t working.
He doesn’t know what the mod was for, or what should be changed back. There were some traces cut also.

Attached are the schematics and somepics of the modules.

There are three boards on the module - TR22D is the main board for the channel, an Intercom board, and an Oscillator board.

There are white & black wires in question, that go under or to the back of the modules. There is also a resistor with one leg detached.

A description from him…
“I’m still not sure where the white taped wire goes but I’d guess the 2 wires that are looped with the foam go to T and U. And the resistor cluster doesn’t at all belong and the 2 cut traces can easily be fixed. I’d guess if I took off the cluster and unhooked the black and white mod wires, hooked up T and U wires, and bridged those 2 traces back together, it just may be back to stock. Just a guess…”

I know it's a lot to take in at once! Any guidance you can give him would be helpful. I can get more pics if needed.

Thanks!

 

[musika]

I recently repaired the oscillator circuit in my console by replacing the 2 electrolytic capacitors. They are usually simple circuits. In your case that would be C11 and C12. Was the oscillator recently working?

 

[Ike Zimbel]

For starters, I wouldn't be in a hurry to undo any of those mods. These desks were not perfect when they were designed/built and often there were fixes that had to be done afterwards. Secondly, who hot-rods a comms module? So, the mods are probably a fix for something. This is just a wild-assed guess, but over the years I have seen plenty of mods/change orders for things like oscillator and talkback leaking into busses etc.
As far as why it's not working...
1) I have seen modular desks from this era be particular about where modules are fitted, so make sure it's in the intended slot on the motherboard.
2) All of those rubber sleeves on the wiring can become conductive with age. Check this thread for more info:
3) All of the blue, axial electrolytic caps are suspect.
4) Ditto the tantalum capacitors.
I'll probably think of more things to check, but that's what comes to mind at the moment.

 

[mixbus]

Thank you both for the great replies and suggestions! I will pass them along.
He is aware of module order and has them in the correct positions.

Something was unhooked there for some reason.
This board originally was in a Civic auditorium, then two recording studios, and now to its current owner.

Initially the oscillator wasn't working. IC1 was missing from the Oscillator board. One was put in, and the oscillator works to the groups and aux.
The biggest thing he wants to work is the PFL in solo, mono, dim, and mute section.

It may be, like suggested that mods were there from the start.

He was planning on replacing the blue caps since several were found to be leaky.

I appreciate all the help. This board has been quite the journey for him.

I'll post updates as we get farther along with this.

-Tom

--------
Tom Jancauskas
Imedia

 

[mixbus]

Oh, and the oscillator will not work to the external out on the desk - which is an XLR mounted on a top panel, and a patch bay point.

 

[mixbus]

Here you can see the white & black wires that go under or to the back of the modules. These have been unhooked for some reason, and he's not quite sure where they go. There is also a resistor with one leg detached. See image below...

Thanks.

 

[jensenmann]

I don´t have a TR22 but a Pro4 which seems to be manufactured the same way according to your pictures. When I refurbished it I had a lot of problems with the wiring underneath the rubber sleeves. The islolation of the wires hardened over the years and caused the wires to break. Thanks to those sleeves I couldn´t see the the broken wires. To make things even worse, removing the rubbers made some wires break, too. So keep in mind that moving any PCB with a certain force may create wiring problems. In doubt measure the connections between the PCB and the end-designation of the wire.

Other than that Ike´s suggestions are spot on.

 

[mixbus]

Thank you! That's good info. I'll pas it along!

 

[mixbus]

The owner of the desk- Eric was considering this...

"what if I were to unhook the resistor cluster, hook the 2 wires where I think they go, fix the traces, and see if it works as designed? If not it would be a super simple reverse and it’s back to where it is now. "

He is thinking he needs to remove the "mod" - the string of resistors to the right of the edge connector- and try to return the module back to what he believes is stock.

I've suggested he just leave the "mod" alone, and try & reconnect the unhooked wires where they seem to go. They seem to have a memory of where they should be. He's said he has an idea of where a few go.

Thanks all..

 

[Ike Zimbel]

A couple of times, recently, I've encountered wires that had broken off, but stayed exactly where they had been for the past 40 years so it was very difficult to see that they were not actually making contact. So, I agree with the "possible broken wires" comment further up in this thread.
WRT undoing the mod, I can not think of a single mod that someone would do to deliberately make the PFL not work, so I seriously doubt that undoing the mod is going to fix his desk.

 

[mixbus]

Thank you, That's what I was thinking....
Same with the resistor that isn't attached. Looking at it now, it seems like it's just come of it's regional on the intercom board.

I am helping him remotely & don't have access to the desk. I am relying on pics, descriptions, and schematics he's sent.

Getting closer!

Thanks all!

 

[Whoops]

Being a desk from 1980 I advice a re-cap of all Electrolytic and Tantalum capacitors before proceeding further.
Lytics are known to dry up after all this years and Tantalum caps fail short-circuit.
I wouldn't be surprised if the problems you are having are due to a shorted Tantalum cap or failled Lytic capacitors

 

[mixbus]

Thank you. That's on the list of things to do. He's already found some leaky ones.

 

[Whoops]

Thank you. That's on the list of things to do. He's already found some leaky ones.

It should be the first thing on the list...
And then test the module after the re-cap of the lytics and tantalum to check it works, before doing anything more

 

[mixbus]

Thank you. He’s planning on ordering caps tonight. It might be a few days till he can get back to the studio to check things out, since a big snowstorm is headed his way.

 

[mixbus]

Hi All,

Here is a little update.
Caps have been ordered and on their way, and will changed out.

The questions/issues now are:
There is a resistor - R90 that seems to have popped out of place on the intercom board near C54. He will put it back next time he's at the studio.

There are 3 unattached wires that may or may not need to be there.
They are:
Two black wires tucked inside their blue insulators near IC3.
A blue wire with white tape all the way to the right side, near IC6 and the big blue cap.

The black unterminated wires, and the area with the string of resistors on the black & white wires, is in the area of the circuit not working correctly.

This is what has him (and me, really) confused. Something should be feeding the red relays, and doesn't seem to be from what has been observed.

Also, the jumpers on the back seem to be a factory mod to the circuit. Or at least old enough to be done as a field service correction.

Any help you can give about what may be going on, and where the wires may or may not go would be helpful. This module hasn't been working correctly since he go the desk.

Thank you!
--------
Tom Jancauskas
Imedia

 

[mixbus]

Hi All,

A little update from my friend with the TR22 coms mod issue.

Turns out they did mod it for use with another type of com system for theater use.
Undoing that mod has fixed most of the issues so far.

Quote from him:

Unbelievable update. I fixed the solo feature!!!!

I poured over the schematics and angle projection and said what the heck do I have to lose? As long as I dont let out the magic smoke. So I rolled the dice and it works!

I decided to undo the resistor cluster and connect the 2 black wires with the blue foam sleeves to T and U. Which is where the clusters were soldered to. Then I bridged the 2 broken traces they’d made for the mod. I also traced the wires In That section according to the schematics and they all seem to be stock so I felt pretty sure I had the correct wires to solder to T and U spots. I fired it up and it works perfectly! Now I still have the one wire with the white tape on the end of it but I still don’t know yet where it goes. I’ll get it figured out.

He is still re-capping it slowly since there are several circuit boards and blue insulators on this particular channel.

That's all for now..
Thanks!