Got a CR-820 via ebay yesterday. Owner describing it as "fully functional, doesn't work". Got it for €18.
Unfortunately a yellow-brown stained smokers unit, but complete and without nicks. I measured the fuses (all ok), tested the power transistors (no shorts) and switched the thing on. The bulbs and the "FM"-Led went on, but no protection relay. Measured all supply voltages, everything ok... except the +30V. Here I measured 2.8V at the output of NPN power transistor. Collector voltage was +48V, base voltage 3.2V... didn't sound right.
The CR-820 has a standard arrangement of zener diode, resistor, cap and power transistor as stabilizer. A quick examination of the PCB showed some questionable solder joints in the area. A few minutes work with the soldering iron later the next power-on gave a sweet "click" of the protection relay.... bias adjustment was easy, and soon the whole thing worked like a charm. Excellent FM reception, and about 60W per channel with a 1000Hz sinus on both channels into 6 Ohm. I'll have to replace the bulbs, use Tuner 600 at the switches and clean the whole thing thoroughly, but this was a good catch at the 'bay.
Martin
Unfortunately a yellow-brown stained smokers unit, but complete and without nicks. I measured the fuses (all ok), tested the power transistors (no shorts) and switched the thing on. The bulbs and the "FM"-Led went on, but no protection relay. Measured all supply voltages, everything ok... except the +30V. Here I measured 2.8V at the output of NPN power transistor. Collector voltage was +48V, base voltage 3.2V... didn't sound right.
The CR-820 has a standard arrangement of zener diode, resistor, cap and power transistor as stabilizer. A quick examination of the PCB showed some questionable solder joints in the area. A few minutes work with the soldering iron later the next power-on gave a sweet "click" of the protection relay.... bias adjustment was easy, and soon the whole thing worked like a charm. Excellent FM reception, and about 60W per channel with a 1000Hz sinus on both channels into 6 Ohm. I'll have to replace the bulbs, use Tuner 600 at the switches and clean the whole thing thoroughly, but this was a good catch at the 'bay.
Martin
:thmbsp:
