API 512b Schematic

[mitsos]

whip out that camera!

 

[jsteiger]

whip out that camera!

+100  ;D

I think we may need a secret handshake or special knock to view this thread!  8)

 

[kazper]

Just don't offer up the Gerber's to the guy walking up selling stuff out of his coat.

 

[mitsos]

yeah, secret handshakes are bad news. They'll eventually cause problems. Look what happened with the VK1...

Keep this **** in the open, no harm... API should be helping their customers. If the Chinese (or anyone else) want to make an exact clone of the 512, all they have to do is buy one, they're cheap.  Investment-wise, it makes total sense.  I understand if they don't want to sell opamps, but schemos? in the old days, you'd get a schemo with your equipment. Look at all the old Urei manuals.

 

[Biasrocks]

API got back to me - and just as I suspected:

"I am sorry but I can't e-mail you schematic for 512b because it is very similar as current pre-amps (factory policy)."

I might have a chance to take some photo's tonight. The problem is with R8, which is connected to the Trim pin on the 2520.

That just sucks out loud, too similar to current products so no schematic???

Pulled my 512c, circa 1997

Reichenbach RE-115K-EPC on the input, good ole AP2503 on the output

2 Opamps in there and a 12volt relay, which I'm guessing switches input polarities.

The opamps are an LM3915N (18-pin dip) and a LF421CN (8-pin dip), which are in the same general
vacinity of each other and I'm guessing are both for the front panel LED metering circuit.

R8 is near the input transformer/relay on the 512c and appears to be a
19R 1% metal film, code Blue,Brown,White,Black   Brown

I don't think it's the same resistor you're after for your 512b.

On the 512c there is no connection to the trim pin of the opamp, in fact I'm fairly
certain that the API 2520 that was in there originally and for sure the Avedis 1122
don't have that pin included on the opamp.

Where's Paul Wolff when you need him.

Mark

 

[Biasrocks]

Isn't she pretty?  8)

 

[Biasrocks]

The full monty  ;D

 

[Biasrocks]

Time for your close-ups.  

Relay, R8, input transformer stuff.

 

[Biasrocks]

Meter driver circuit.

 

[Biasrocks]

The best for last.  

Under the 2520 tree.

There is no connector for the Trim Pin on the board, it's omitted.

 

[mitsos]

Bias, you ROCK!  ;D 

but I can't believe for $900 they can't clean the topside of the board.  :

can you tell the value of the feedback cap?

The LF412(?) is probably some kind of rectifier for the 3915 (although I think there should be another 4148 somewhere?) What's the other diode? 

No help on the trim..  Hopefully if you post pics someone can help with it.

 

[Biasrocks]

Bias, you ROCK!  ;D 

but I can't believe for $900 they can't clean the topside of the board.  :

can you tell the value of the feedback cap?

Yes, I noticed the flux residue on there. These were manufactured before the ATI handover, so I'm sure they look a bit different these days.  :

Feedback cap, are you talking about the electrolytic cap C20, 2u2/50volt?

Mark

 

[mitsos]

no, c14, under the opamp.

EDIT: look different these days? Yeah they use a brighter blue soldermask...

 

[Biasrocks]

no, c14, under the opamp.

EDIT: look different these days? Yeah they use a brighter blue soldermask...

C14 is a silver mica 10pf, 300v

DZ1 is a 1N47?? with "8.2v" printed on the circuit board.

So I'm thinking it's a 1N4738A.

Mark

 

[mitsos]

10pf    wow, that's aweful low... I'd think it'd be closer to 100..

 

[Biasrocks]

10pf    wow, that's aweful low... I'd think it'd be closer to 100..

The code on the capacitor was 100J, 10pf 5%.

Mark

 

[mitsos]

Thanks, I think that's actually 100, which sounds more like what they would use. Not 100% positive but I don't think they use the significant digit notation like ceramics.

 

[OneRoomStudio]

Sorry it took so long, here you go:

I darkened the area where the resistor burnt up. I thought it was connected to the trim pin because of this image I have:

I think it may actually be the output pin. I'm guessing the 2520 is fried and I can probably just replace the resistor and pop a new one in, but I don't want to risk it until I know what else could be wrong....

 

[Biasrocks]

Sorry it took so long, here you go:

I darkened the area where the resistor burnt up. I thought it was connected to the trim pin because of this image I have

Oddly enough that data sheet appears to be reversed, the trim pin is actually on the left corner, not the right, it's the view if you look at the 2520 from the bottom instead of the top. If you look at the photo I posted (which I suspect you already did) which includes the Avedis 1122; that's the correct pin-out.

It looks like the value is printed on the circuit board, 47R.

That would be a 47 ohm 1% metal film resistor. I'd put a 1/2 watt-er in there to be safe.

Why not replace that resistor, power it up and take some voltage readings without the 2520 inserted to be sure you're in a safe range before you pop in the 2520.

Mark

 

[Greg]

What's the deal with the extra DIP-8 on the 512C by the meter driver circuit... I don't see it on the 512B.

Perhaps a servo?