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Monday, November 13, 2017

Beomaster 1900 (Type 2903): Trying Out The Recapped Beomaster

I partially reassembled the Beomaster 1900 so I can check out my recap work and begin the amplifier adjustments. It is always an anxious moment when you first re-apply power having completely disassembled a unit.

This Beomaster powered right up to Standby mode and touching the FM5 terminal post put the receiver right into that mode (no FM antenna is connected yet). A great feeling for sure.

To get from the disassembled recapped boards to this first power on test I prepared the PCB 2 board for the No-Signal Current adjustment.

That adjustment will require measuring the voltage across the left and right channel emitter resistors while adjusting trimmers R259 and R359. I decided to install new trimmer resistors for those two devices. I didn't want to discover those old trimmers are a problem and have to remove PCB 2 again.
Here are the new adjustment trimmers installed.

The next step was to re-attach the four heat sinks for 2IC200/300 (TIP 141 Darlington pairs) and 2IC201/301 (TIP 146 Darlington pairs). The original mounting used thermal paste/adhesive to mount and insulate the transistors to the heat sink. For the re-assembly I decided to use a Thermalloy thermal interface product. It doesn't dry out like the paste and is less messy.

Tomorrow I will test the power supply voltages and do the No-Signal Current adjustments. Then I will see if I get output from the amplifier section.

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