Dead Crimson Pre - Help needed

The weekend produced a problem in that my friends Crimson 610 Pre appears to have died for no known reason, not even a live LED & no fuse to be seen.

It's powered from the Power amp in this case, unlike my own which has it's own wall plug so I was wondering if anyone had the schematics (I think it's an old circuit?) for this amp & what it's getting supplied & connections from the Power amp before I go in all guns blazing?

for once I'd like to do this right as it's not my own so I feel I should take the time to get it spot on.

Thanks,

J

 

Where are you/ the pre.....?

Have you used a multimeter on it ?

 

Edinburgh, unless you mean do I have access to the pre?

Currently sitting next to me with it's 'home made P/S'!
I've checked the components I can with the MM & replaced one capacitor that's was clearly burnt out once I'd spotted it tucked behind the main caps. From what's been said on PF, the supply made for this is wrong. It's output is +12V with GND, not -12V and I don't even know if this is the correct voltage. Again that pretty much matches with the cap blowing on one channel.
I guess basically I'm going to have to prise the power amp from him to get the correct supply & find the voltage then try to make up an umbilical between the two...hmmmm

Does anyone know the connection schematic between Crimson Pre's & power's? T'woud help get this going a bit quicker.

Ta,

J

 

It should not be too hard to sort out ..what are the connections

If you supply the wrong polarity it will not work at all...did I miss something I thought the unit had been working?

some pics would help.....either on the forum or pm me

 

Interconnect sorted, the power amp gives out -38, 0V, +38V.

I'm getting -38V on one rail and 14V on the positive rail in the preamp.
Nothing obviously wrong with the components & without the schematics it's hard work tracing it through.

I am confused as to why the power LED isn't lit when power is supplied though.

Bet this is really obvious to a better person than me!

J

 

OK
that should not be too hard to find..... where are you measuring the voltage ?

the transformer seems ok... and if your getting dc the rectifier diodes must be working.

so it must be the voltage regulators

 

No sign of regulators at all, this this is discrete transistors all the way and the power amp is fine, the pre is just parisitic in the same way as the Naim pre's are.

Measuring the voltages as they enter the main boards & also at the main supply caps.

J

 

The normal way things work is that you have a transformer to drop the ac from mains to near the dc required, then rectification to turn ac to dc then voltage regulation to provide the dc rail with the correct voltage....I know of no other system! that of course dosen't account for the filter caps or multiple secondaries on the tranny. But if you have a dc rail voltage problem you need to look "up stream" for the problem the voltage regs will look like to92's style packets look for Lt78** or lm317 style devices [** will be the voltage ].

 

Meant to post these a bit ago but lost my connection....






Anything there that is likely to blow from sticking +24V & 0V across the P/S inlet?

You can see the temporary cap I replaced at the bottom of the first pic, the purple Sanyo, should be a tant.



J

 

So thats the pre amp ........no big power trannies so must be....

if you can get a pic of the power in and the power out areas ...you have done it but I still can't make out what goes where.

You can do loads of damage if you get things wrong with 24v !

 

Sorry it needs to be infront of me with a multimeter its too hard to follow other wise.

 

Yeah, was thinking that so it'll have to be a full removal of the board & if push comes to shove & nothing is found it'll be replace all bits until it works (the hacking approach).

Cheers for the help,

J