Hi 6502,
congratulations and welcome. Glad that yours is working.
I'm happy to share and collaborate. I sent you a PM so we can have small signal-to-noise discussions without cluttering the forum, if you like.
Speaking of cluttering, my first attempt at the attenuator operation schematic is misleading and i'm going to remove/replace it.
I also noticed the problems with the design diagrams you mention. Yes, it is a real piece of german engineering. More like german desperation to get something that meets the specs
![Cheesy :D](https://www.eevblog.com/forum/Smileys/default/cheesy.gif)
This is particularly apparent in the attenuator board. The schematic does not match the component placement diagram, but the component placement diagram is matching my physical board. According to their timestamps, both have been made with only one day between them. How have they come up with this ?!
I'm not sure, but it might be that they had several different iterations of every board in production.
I guess willi was hinting at this mentioning the different versions for the attenuator board.
Here's a list of what's in my device physically:
- Grundplatine,backplane,6040 S GR 3
- Microprozessorplatine,cpu board,6040 MCS 3B
- Vorverstaerker, pre-amplifier (DC), 5020 v7
- Anzeigeplatine, display board, 6040 TAW 4
- Trafoplatine, power transformer, 5040-T-4
- Digitalplatine, amplification control,6040 D3
- Integrator, integrator board, 6040 I-4
- Ohmteil, Ohm board, 5040 O-7
- Abschwaecher, attenuator, 6040S ab 3
- Ohm relais, Ohm relays, RER/6040S OHM
- Wechselspannungsvorverstärker, pre-amplifier (AC), 5040 VW 4A
- Gleichrichterplatine, rectifier board, 5040 G 3a
I omitted the display and key interface board for (my) convenience
Here's the boards front- and backsides: see below
Here's also a text file of the bill of materials from the manual available on prema's website : see below
Your findings on the U3 sub-circuit are astonishing. So far, i was inclined to go with kleinstein in assuming it is a AD 234 or AD 261. Their pinout seems to be compatible with whats on the board. That together with U4 as a low-pass filter against the chopper noise seemed to make sense.
Datasheet is here: check below
After reading your mail, i went back and measured the width of the black box. It is at 36mm too small for the 38mmx38mm 234 package.
It is hard to believe they went an built something custom.
You mention that the disassembly of the black box should be easy. To me, it looks more a one-way option. I don't know how to safely disengage the blue pin connectors.
Plus, there's probably a metal foil sheet and other nasties before you even see the components. How did you do it?
So far, i was unable to find a DC feedback path into the inverting input of U3. Is the feedback directly implemented in the sub-assembly?
It's not uncommon that only one set of jacks is connected internally. This was probably done to reduce thermal and noise in general.
In my case, it's just the front that is connected. The wiring from attenuator to front panel is straightforward, i'd be happy to describe in more detail, if you like.
The ratio module is indeed interesting. I have to see one yet. The DAC, BCD and RS232 are less appealing, after all there's a GBIP interface ?
I have a 2716 somewhere, but don't know the 2758 or where to get the required image.
...My attachments are apparently too large, am looking for a way to upload them
...here you go:
https://sabercathost.com/folder/355525/prema6040s