A have an old Gradiente Esotech DR-5.5HT that was turning off a few seconds after turned on. Gradiente was a Brazilian company that uses, in some cases, equipments from another vendors until has his own projects. This is one of this cases. Internally the equipment is a Sherwood Newcastle R-756. I found its diagrams on internet. Let us see! You can find on Google searching for “Sherwood R-756 schematics”

After some research, , I found that the central processor, a Sony CXP82860, controls the power supply.

The power supply relay is controlled by the ST/BY-RLY pin (stand-by relay). Then, the central processor is turning off the equipment. We can see, in addition, a pin called PROTECT. This pin receives a signal from the equipment main board. When I disconnected the flat cable from main board, the equipment do not turn off anymore. Then I can see the PROTECT signal is telling to the processor that is something wrong.

On the main board circuit, the PROTECT line come from the power supply and from the amplifier board (yellow). When I disconnected the amplifier board the fail remains, then the problem (in my case) is on the power supply.

This equipment has four power supply circuits:

• +6V stand-by, that is always on.
• +60/-60V, the amplifier board power supply
• +15/-15V
• +5/-5V

When I disconnected the 60VAC plug, the problem disappeared. Then I know the problem is on the +60/-60V. I took out the capacitors and test them, then I found one of this is not working.

After changing the capacitor, and clean-up the mess from the leak dielectric from it (I was thinking it was some type of glue), the equipment came back to life! Great!

Then, if you have a similar problem, my suggestion is:

• Disconnect the amplifier board to check if the problem is on the power amplifier.
• Check the voltage on correct points: +60V, -60V, +15V, -15V, +5V, -5V. There are two 5V regulators (7805).

If you have luck (like me), the problem will be on the capacitors! Well, it’s a 20 years old equipment!

Good luck.