SD1127 RF Power Transistor Driver Check
Paul Hollings
Aareff Systems Limited
https://www.linkedin.com/in/paulhollings
A complete new replacement block can be purchased from https://www.aareff.com/en/replacement-100W-and-200W-transmitter-amplifier-blocks
For this test the amplifier should not be powered by drive or AC.
To actually check the SD1127 electrically you need a soldering iron. Shown in the picture below is the power amplifier PCB. In the yellow square there are some components soldered. One of these component leads is the SD1127 (base) input. It is difficult to see from the picture, but if you have the real thing in front of you, you can see the SD1127 underneath the little square board and the lead disappearing into the hole. You need to warm the solder up and lift this input lead off the board so that it is in total isolation poking into the air and not touching anything.
Again for these measurements a standard low cost digital voltmeter is sufficient, but please make sure the meter batteries, leads and probes are in good condition to avoid false readings.
Turn the selector on the meter so that it is pointing at the Diode Check symbol shown in the red circle marked on the picture. Connect the RED lead to the V/mA connection and the BLACK lead to the COM. Different multimeters will vary with the select position of Diode Check and the labeling for the RED and BLACK lead, but you should be able to figure it out.
Hold the RED lead on to the SD1127 input lead (base) that is poking into the air, make sure it does not touch anything else and you have a firm connection. Keep it held in position.
Then 1st Check - Put BLACK lead on to point labeled DRIVER DC shown on the diagram. The meter should read between 0.65 and 0.75V.
Then 2nd Check - Put BLACK lead on solid ground point, in the diagram I have shown the soldered joint for the main output transistor as this is easily accessible. The meter should read between 0.65 and 0.75V.
If the two measurements are okay then the SD1127 is good and the fault is elsewhere. If not the SD1127 has blown and needs to replaced. This is not an easy job and you may need to send the amp block back to us, it depends on your level of experience.