Crest Century TC Channel Repair

[la80vette]

Hello to all Members,
I'm brand new to the forum. I'm curious if there is a repair tech that's close to me (south Louisiana) that could repair or upgrade about 10 channel strips from this console.
I haven't been able to find a tech and I don't have the knowledge or the equipment to accomplish this. Also, I don't have the schematics, only the diagrahm and Peavey won't respond by phone or email. this board was built just before the Peavey purchase.
Thanks to all.

 

[Brian Roth]

In another post, you mentioned the Crest has multiple dead or low level output channels. FWIW, in a mixer that is 20+ years old, the most likely problems will be old electrolytic coupling capacitors in the signal path.

Bri (who is NOT close to southern Louisiana <g>)

 

[la80vette]

Well at least I have the 22 working channels.
Thanks Brian.

 

[Brian Roth]

Replacing coupling "lytic" capacitors is a known part of maintaining old desks. Some desks "eat" the lytics quickly due to high internal temperatures .

As the caps age, the first thing commonly observed is a slow "droop" in the low frequency response along with a lesser drop in level across the entire audio band. As the caps get worse, you end up with low level across the entire frequency range until....no signal at all when the cap essentially becomes an open circuit.

Bri

 

[Brian Roth]

Back to the internal operating temperature of desks....

A lot depends on which opamps are used. Desks using many 5532 and 5534 chips run a LOT hotter than ones using chips like TL0xx.

I believe it was the Neve VR desks that "ate the caps for lunch".

Some of the heat problems are magnified due to internal design, like circuit boards stacked inside a module which trap the heat and cook the caps.

I am not all that familiar with the various models of Crest desks, but I can comment about some other "mainstream" desks from years ago.

MCI JH-636 desks eat the small lytics located in a tight area around the EQ circuitry because multiple 5532 opamps and the coupling lytics are in a "heat cage" due to the accompanying daughter board.

OTOH, Neotek desks typically used cooler-running TL0xx opamps in a more open layout.

Bri

 

[Whoops]

I believe it was the Neve VR desks that "ate the caps for lunch".

Ohh yeah, VR consoles were prone to a lot of problems and failures due to excess internal heat, their competitor at the time didn't have those problems at all so I think that's one of the reasons SSL 4K consoles got so Popular in the 80s and 90s.
Compared to VR consoles the 4K were really sturdy and dependable

 

[Brian Roth]

I might have to do a "back pedal" re. Crest desks and coupling caps being in the signal path.

I found a PDF for a Crest V12 on my drive and took a peek. Egads! No coupling caps anywhere besides the phantom blockers on inputs to the mic preamp!

A look in the tech docs section of this forum and I found the schemos for a Century VX.....NO coupling caps! I see some servos scattered around and higher-class opamps everywhere.

https://groupdiy.com/threads/crest.44961/
Both sets of schemos have 1990's dates. I don't know if the Century TC is cut from that same cloth, but my finger pointing to coupling caps might be wrong.

Bri

 

[JohnRoberts]

Hello to all Members,
I'm brand new to the forum. I'm curious if there is a repair tech that's close to me (south Louisiana) that could repair or upgrade about 10 channel strips from this console.
I haven't been able to find a tech and I don't have the knowledge or the equipment to accomplish this. Also, I don't have the schematics, only the diagrahm and Peavey won't respond by phone or email. this board was built just before the Peavey purchase.
Thanks to all.

Well at least I have the 22 working channels.
Thanks Brian.

If you have 22 working channels I would start by measuring them. A common failure of old tired electrolytic capacitors will be weak LF response. Replace any marginal capacitors you find in all the channels.

To troubleshoot the bad channels having good channels to compare may be useful.

JR

 

[Brian Roth]

Hiya John. As I mentioned in post #7, I have found two Crest desk schemos from the 1990's which have NO coupling caps. I need to figure out how to split the V12 desk schemos I have locally since that PDF is too large to upload here.

Bri

 

[JohnRoberts]

Hiya John. As I mentioned in post #7, I have found two Crest desk schemos from the 1990's which have NO coupling caps. I need to figure out how to split the V12 desk schemos I have locally since that PDF is too large to upload here.

Bri

That stuff is from before my time... I recall that JP (RIP) liked to use DC servos (that still have film caps in them). If a non-working path has excessive DC on it that could be a servo failure (bad op amp?).

Caveat this is mostly guesswork.

JR

 

[Brian Roth]

I managed to split the V12 schemos in half to meet upload file limit sizes here...as well as another one I found on my drive which DOES have coupling caps all over the place, beginning here:

https://groupdiy.com/threads/crest.44961/post-1064133
BTW to John....who is "JP (RIP)"? I presume Mr. Crest?

I find it odd that two of the Crest designs had no coupling caps, yet one did, from the same 1990's time frame.

Bri

 

[Brian Roth]

JP name mystery solved:

https://en.wikipedia.org/wiki/Crest_Audio
Don't recall meeting Jean-Pierre (John) Prideaux, but I encountered a variety of Crest products over the years. Power amps and a few desks. Good stuff!

Bri

 

[JohnRoberts]

JP name mystery solved:

https://en.wikipedia.org/wiki/Crest_Audio
Don't recall meeting Jean-Pierre (John) Prideaux, but I encountered a variety of Crest products over the years. Power amps and a few desks. Good stuff!

Bri

Sorry wrong... I was referring to John Petrucelli, now RIP. He was lead console circuit designer for Crest when Peavey purchased them. As I recall he liked DC servos. John was the "P" from APB the console company that spun out of Crest.

I was on the tire kicking crew when Peavey purchased Crest, but I knew John from years earlier when he purchased stuff from my old kit business.

JR

PS: I never heard of Prideaux but its in wiki so it must be true...

 

[la80vette]

AFAIK, the Century SP, TC and GT were prior to the VX and before the Peavey aquisition. All models (at least the TC and GT) share the same PCB.
There was also an option for a transformer on the TC and GT card but probably for Isolation and not step up. I believe it was a 1:1 transformer.
Like I said before, I got this desk for free but really not interest in putting a lot of money into it if it wont be great in the end. Somewhat of a shame though as this board is built very well, completely modular, very simple to pull a channel strip and the rest of the desk will even run with a strip pulled.
Also Gary at Crest/Peavey in MS. returned my call (very nice guy and helpful). Unfortunatly, He had no documents to share on this pruduct and said Peavey
didn't take any docs after the purchase.
I do have the operating manual which I got online but it only has a block diagrahm.

 

[la80vette]

John,
Would you think that maybe APB might have the schematics for the crest TC?

 

[la80vette]

Correction; The Century SP and TC share the same pcb. The build date on the card says 2/1/1993.

 

[JohnRoberts]

John,
Would you think that maybe APB might have the schematics for the crest TC?

It doesn't hurt to ask but I would not expect much.

JR

 

[la80vette]

I going to atempt to repair just one channel. The strip 9 aluminim electrolytic caps and a ton of I think film caps. Please excuse my ignorance. Would I need to change everything or just the aluminum ones.
Aluminum caps are:
7) 22uf 50v
1) 1uf 50v
1) 22uf 50v but its different. it's labaled CKRN B 85 degree C

 

[la80vette]

The opamps in the Preamp section are:
2) TLE2082CP
1) PMI SSM 2017P
Do these need to be changed as well? Are there better options for opamps?

 

[JohnRoberts]

I advocate measuring first then addressing shortcomings.
===
I suspect Crest specified adequate op amps... Maybe review the data sheets to look for newer versions.

JR