I was recently enlisted to set up a “new old stock” CS-540V repeater for use by a local ham radio club. The repeater was pristine and had obviously never been used. I was able to obtain a copy of the programming software from the manufacturer, even though the repeater was over 14 years old.
Using the Windows programming software, I configured receive and transmit frequencies, PL, timeout, ID, etc. I adjusted the power output to 25 watts per the clubs request and set about to test the machine.
During testing, I noticed the output power would drop to zero and after a cool down period, would come back up to full power.
I came to find out that this model of repeater had a design fault where the power amplifier brick that was fitted (Mitsubishi RA60H137M) had a flange on either side of the mounting surface that was not flush and thus there was a 0.5mm air gap between the bulk of the module and the heat sink of the transmitter chassis. Removing the module, you could see that the thermal compound had developed deep fissures where there was air. This obviously caused the modules substrate to crack, opening up a trace between the various stages of MOSFETs on the circuit board as soon as the temperature increased.
A new SAV32 module was procured from rfparts.com. This module has a flush mounting surface.
In order to achieve full power output, the RF power control circuit would need a slight modification to achieve the right gate voltage at the module that’s controlled by a LM358 operational amplifier circuit through the transmitters microprocessor. I replaced a 1k ohm SMT resistor with a 470 ohm resistor in the circuit between the output of the op-amp and the gate control pin of the RF output module.
Once this was done, I was able to adjust the power output to 25 watts.
This repeater includes a very basic controller. An external controller could be connected via the 25 pin accessory connector on the repeater.
The repeater controller includes the ability to send a periodic ID and there is a checkbox that should tell the repeater to only send the ID if there has been activity. However, the ID seems to be sent every 10 minutes (configurable) regardless of repeater activity, under both settings of the checkbox.
After a few days of operation, the repeater ID went away entirely. Reconfiguring it remotely over the air restored the ID for a few more days and then it quit again. Oddly, changing the speed of the ID from 22 wpm to 11 wpm restored the ID for a longer period of time, but it went out again! Changing the speed back to 22 wpm has restored the ID for over a week now. I’m keeping my fingers crossed that it continues to behave!
We may have to install an external controller to rectify this problem.
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