Topward 6306D power supply won't go below 4V

[alsetalokin4017]

So I was powering some crazy experimental apparatus and suffered an "event" that killed the Topward 6306D dual tracking power supply. I had a spy infiltrate the Topward service center in California and he obtained a schematic for "nearly" the right unit. Troubleshooting found several bad op-amps and voltage references on both the Master and Slave boards. Replaced those and now everything, all functions, are working fine again... EXCEPT that I can not turn the Master side down below 4 volts. The lowest it will go after considerable warmup time is 3.7 volts. All voltage settings, current limiting, tracking, parallel and series, meters, indicator lights, all of that is working fine. Only fault is the minimum voltage on the Master side, I should be able to turn it down to zero.

Any ideas? Unfortunately the "nearly right" schematic filesize is too large to upload. For some reason Topward schematics are hard to get hold of, at least for me (at least for free.)

(sorry I originally attached the wrong schematic and the nearly right one is too large to upload.)

[alsetalokin4017]

Let's see if this works. I took screenshots of the nearly correct schematic (for a 6606A but as far as I can tell the circuits are the same except for the meters).

[alsetalokin4017]

--- aaaaand one more:

[Ordinaryman1971]

I am no certain but I would suspect one of your opamps is not working right. I'm working on BK Precision 1670... not sure of the exact model with exactly the same problem.
I've socketed the opamp and tried few the ones I have, had to put it to the side for now,ran out of time, but it was my first suspicion.

[floobydust]

4V is a big offset, if the output won't go to zero volts, it can be a damaged driver/output transistor, or problems with the control op-amps.

Because you have replaced a bunch of parts, the calibration is also off. Maybe first try the cal trimpots, see if that has enough range, otherwise there are still damaged parts.

I think the power supply has calibration trimpots for zero and max. output voltage and slave tracking. Some PSU's have trimpots for min (VR16) and max output current. These are different from the panel-meter calibration trimpots.
You can get the current-control op-amp fighting the voltage-control op-amp, if the offsets are not zeroed out.

[torittog]

  Hi, I have a problem with the horizontal deflection of a 7045 oscilloscope.
I only see the right half of the wave.
I'm looking for the power supply and CRT circuit diagram. can you help me?

Thank you very much, G.

[neil]

alsetalokin4017 - you've made my day. I just got a semi-dead Horizon DHR3655D-10 power supply that seems, at least externally, to be the identical twin of the Topward unit, and I was having no luck at all finding a schematic for it. I haven't looked inside yet to compare it with your schematics, but I think they're going to be a huge help. Thanks so much for posting those!