dbx 411 NR what is 'QA' on the silkscreen?

there are a pair of silicon devices with 5 leads each thermally coupled, labeled QA1 and QA2...there is another dip8 chip--QA3 that has its label rubbed off, I'm guessing these are the heart of the dynamics processing

anybody have a schematic or any advice

i have determined the thermally coupled chips are a matched npn and pnp pairs, i will try them in a doa circuit some day (there are 16 of each), these and some to-5 transistors and maybe tantalum and styrofoam caps can be salvaged,


does anybody think it wrong to canabalize the 8 NR cards??

There is a bit of a service manual with partially relevant schematics on the DBX site now.  Did you ever determine any useful cannibalization with these? 

I meant to respond to your inquiry re: converting to 900 modules. it is possible though I don't know if the backplane can be used--the slots are offset for VPR. I've got it to fit 51x with some fabrication--rails to hold card edge connectors.

If you remove all modules there are a few screws that sit flush behind the module flange rails, these screws retain the bar that has the guide slots and 6-32 threads. either machine down this piece or replace it with bar stock and cut new (4-40) threads ...also to widen the opening (900 is same as 500 I think) you can remove the frond horizontal rail parts and flip them.

As for other useful parts I've got the Haako ready to extract 15 pin card edge connectors if a need arises.
the only component of potential value:
http://www.studioelectronics.biz/sunshop/index.php?l=product_detail&p=1338

Thanks.  Seems those are being offered at about the price whole 411 cards sell for at times. 

The 411's work in the 900 rack fine, so I think it really is just the front panel metalwork on the 208 rack.  I haven't seen a 158 rack in person to know about that one.  PSU capacity is the biggest unknown, and I don't have them in front of me to look ATM.  May well be less with the 208 than the 900.  Easy problem to solve, if one wanted. 

what is that? looking for complete 411 cards?

No.  I have a 208 rack full of 411 cards.  Sorting out what to do with it; repurpose 208 for 900 use, hack 411's for ? 

etc

@shabtek sorry to bump such an old thread but have you concluded on what the QA1 and QA3 Transistors are? I am currently in the process of restoring some old DBX 900 series modules and on 2 904 Modules that i have AQ1 and QA3 have been broken off the PCB due to storage or impact from the previous owner.
Looking into replacing those but i have no way to determine the the transistor models and matching values.

They are a dual matched pair of transistors. QA1 is PNP and QA3 is NPN. Chances are they should be able to be replaced by one of several functional equivalents if you can obtain them. A PNP substitute would be uPA75V. For NPN, uPA74V or 2SC3381. These are probably pin-compatible. The middle substrate pin (if there is one) may need to be bent, depending on the location of the hole.

Having said that, those substitutes are hard to find these days. Because of the lack of thru-hole dual transistors, and SMD transistors are readily available but mostly to small to easily mount, I have ordered a custom tiny pcb with a BC846BD equivalent, which is intended to be a drop-in replacement.