Well I guess it time to decide what to do with the Thurlby PL310 after all the flipping time I've spent on it and the trouble its been, so I'll just have to put it on one side and wait for the time being........ until I need to use it. Yes that does indeed mean that its fixed and working again and ready for active duty, the little beauty.
It was offered to me by Ice-Tea almost a month ago now and jumped at the chance of having another nice piece of TTi gear at my disposal. It was just as Ice-Tea described it, totally unresponsive with the output voltage displaying 40.95V with no control over it at all. Plugging in my Brymen revealed that the true output voltage was some 51V, a far cry from its supposed maximum of 32.1V.
Next there was the searching around on the internet for the service manual and after many downloads, eventually found one that had resemblance to the boards fitted inside it. Once it arrived, I opened it up and was surprised to see it looking like new inside, no sign of the usual dust and grime. Started pulling a few caps out and testing them, some had a ESR of 12
so that was not ideal, so ordered a complete set electrolytics for it. Then discovered that the 2 regulators on the driver board had decided to curl their toes up and die along with the pass transistor (2N3055) so these were also ordered as the Op Amp was also inexpensive, order that as well.
The parts came in, and they were all fitted, and I was very pleased to see that I now had full control over the voltage on the controls, however that elation was short-lived as it was fine as long as the unit did not have a load connected. Even a 1K resistor was enough of a load to bring the voltage crashing down to 1.8V
Then started a head long dive into a rabbit hole, pulling everything on the main board off that had anything to do with the voltage and current controls, everything tested OK and yet the problem still existed. Next I dragged out the microscope and started checking for cracks in the traces and dry joints, then reflowing all the joints, still the problem persisted. I even got to the stage where I suspected all the Zeners on the board, although logic, along with a few members, told me that they were fine.
I even started talking to TTi technical dept, and they told me that they nobody working there now that knew about the "brown" power supplies but did furnish me with a service manual for the brown series of PL310's. The manual, as it turned was for the older models series 1 and 2 of those supplies. I sent them photos of the boards, and they then identified it as their newer grey series, even though it was in a brown case. A suitable service was then emailed to me along with an explanation that, although it was in a brown case, it was really a grey series and when they introduced the new model, they had a load of brown cases and they decided to use them up first.
Edit: this is split into 2 parts because of the number of photos.
The dammed forum attachment bug got my photos and screwed up the order they were shown in, rectified that, thats why mnem sussed it out.