Studer A800 channels 9-16 dead

[jwhmca]

Hi Guys,

Channels 9-16 are dead. When I switch to sync the 9-16 status lights go out. Not sure if that has anything to do with it?

 

[Walrus]

Are you talking about the status lights below the meters or on the remote and which ones?

Loose multi pin connector on the back of the meter bridge?
Power supply dead?

 

[jwhmca]

Yes, the status lights below the meters.

Is there an easy place to probe and test the power supply? I've heard you can swap them around to test them. Procedure? Does the manual have a section on "service positions"?

INPUT and OUTPUT will light up, just not SYNC light

I have checked the Multipin connector.

 

[Brian Roth]

It's been more than a few years since I messed with an A800, but the power supplies can be swapped around.  The manual has detailed info if you dig around in it.

Bri

 

[Walrus]

You can swap power supply connectors by tilting the deck plate and then folding out the audio electronics assembly to access the plugs. Be careful with the assembly as it is VERY heavy! You do not have to physically move the supplies themselves around.
My experience has been that it is usually one of the bridge rectifiers in the psu that fails.

 

[jwhmca]

Does that symptom make sense for a power supply?

Is it okay to run the supplies with no load?

 

[sodderboy]

If 9-16 light and play in REPRO then it is not the supply.
If the lights are on before switching to SYNC, then I would check/re-seat all control/remote cables behind the meter panels.  Powered-down of course.  Most logic issues are simple cable re-seating.

You can operate a supply without a load no problem.
If you tilt that front card cage down, make sure the machine cannot roll backwards.  As said, the cage is very heavy and the tendency is for the weight to push the machine away from you.  The power supply cables are sheathed in gray tubing so easy to ID.

As designed the supplies run VERY hot, and the filter stage of the supply gets baked, wires and all.  One trick for 120VAC users is to run the supplies, the three audio supplies only, at the 130VAC switch setting.  It reduces the amount of energy sinking to ground and dissipating as heat by about 20% and the rails keep their rated voltages.  I recommend this to customers after a re-build.
Mike

 

[jwhmca]

9-16 REPRO lights work, but they don't have any sound.

 

[sodderboy]

Prolly the supply then.  Swap with 17-24, with the machine off.

Have the audio cards ever been re-capped?
Mike

 

[jwhmca]

Yeah, it looks like it's had an extensive recap.

 

[jwhmca]

Looks like a bad power supply for sure. Blown +15 supply - fuse - power transistor.

I don't think you can run this with out triggering it to turn on in some way? Out of the studer none of the supplies will run?

 

[Walrus]

That's correct, there is a triac in the supply line so that if a 8 or 16 track headblock is fitted, the machine shuts down the redundant channels. You can use a short crock clip jumper on the right spade terminals at th end of the pcb to bypass the triac and power up the supply. If you dont have a manual, it can be downloaded from the Studer ftp site.

 

[jwhmca]

Thanks for the info Kevin,

Are you talking about the card? Which set of spades? I see two on here...

 

[Walrus]

It's the 2 brown wires at the top right of the pcb in your picture. 
I only jumper them and power up the supply once I'm happy I have found and replaced  what blew the fuse in the first place.
I've only once had a transistor fault, all other times it has been the bridge rectifiers.

 

[jwhmca]

Seems like it was just the 6.3amp slo-blo... any common issues that may make for a intermittent fuse blower?

 

[mjrippe]

Seems like it was just the 6.3amp slo-blo... any common issues that may make for a intermittent fuse blower?

Fuses, like incandescent light bulbs, sometimes blow on power-up just because they are old and "worn out" from many power cycles.  If it blows again soon, you have a problem.  If it was the original 6.3 from the factory (how would you know?) then it was long overdue to blow.

 

[jskylab]

And instead of jumpering the two brown spades could you simulate the headstack by using a +24V psu on brown pin 17 and then shorting pin 15 and 4?  Would this be a good way to check the triac circuit?

Jeff