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My repro amp duplicates the original functions of the amp, so fully automatic climate control is provided. The analogue control circuity is the same as the original, the difference is in using a solid state motor controller chip instead of the two relays.
The optional LEDs indicate power on, system demanding more cooling, system demanding more heating.
I could not source the multi-pin connector plugs, so the repro amp is supplied with flying leads for the user to splice the original plug onto.
Great. In the manual it says to test the 3 diodes if the purple and red wires don’t respond to changes in temp.
My AC works intermittently (sometimes ambient air with low fans and sometimes responsive and working well). I suspect the amplifier but want to confirm it.
Where do I find the 3 diodes?? Are they the ones you reference in the thread above?
Yes the three diodes are hidden in the wiring of the servo itself. They are relatively unlikely to have failed, but could have dry solder joints to the little circuit board onto which they are mounted.
Your symptoms sound fairly typical of a flaky amp. The contacts in the relays can fail after 40 odd years of service and they cannot be replaced as the whole amp is encased in resin. To end up with this working design of replacement amp, I spent ages melting and picking off the resin from an old unit and then reverse-engineering the circuit. The amp uses 8 transistors, whereas the circuit diagram I worked form originally, which was in the Delanair service book, used only 6. I found out that this is because they were the very old style germanium transistors with different characteristics to silicon ones. The germanium trasistors were phased out in the 1970's. Suffice it to say, I ended up putting in a lot of research time to get to a working unit!
Here is a page from my notes on checking the system with the amp removed. Note that, if the servo is fully driven to one end or the other, it will trigger the limit switches and so you will only see continuity in one direction with a multimeter due to the diodes. This means you might need to reverse the multimeter leads when testing depending which end the servo has driven to.
Yes the three diodes are hidden in the wiring of the servo itself. They are relatively unlikely to have failed, but could have dry solder joints to the little circuit board onto which they are mounted.
Your symptoms sound fairly typical of a flaky amp. The contacts in the relays can fail after 40 odd years of service and they cannot be replaced as the whole amp is encased in resin. To end up with this working design of replacement amp, I spent ages melting and picking off the resin from an old unit and then reverse-engineering the circuit. The amp uses 8 transistors, whereas the circuit diagram I worked form originally, which was in the Delanair service book, used only 6. I found out that this is because they were the very old style germanium transistors with different characteristics to silicon ones. The germanium trasistors were phased out in the 1970's. Suffice it to say, I ended up putting in a lot of research time to get to a working unit!
Here is a page from my notes on checking the system with the amp removed. Note that, if the servo is fully driven to one end or the other, it will trigger the limit switches and so you will only see continuity in one direction with a multimeter due to the diodes. This means you might need to reverse the multimeter leads when testing depending which end the servo has driven to.
Spoiler
You might try contacting SNG Barratt directly for more details on sourcing just the plugs. Additionally, checking with automotive salvage yards or specialty electronics forums could lead you to a suitable connector or similar alternatives. I was struggling to find a good service that fit my budget until I found academized.com/cheap-research-paper The price was affordable, and the quality of the research paper was impressive. They delivered a well-written paper that met all my requirements. If you’re a student looking for cheap yet reliable research paper help, this is definitely a service worth considering. It’s saved me time and stress, and I’m really happy with the results.
