Yesterday I have done the transmitter signal tracing using my Velleman PCS500 pc-based oscilloscope. Here are the results:
PRE (0.04-0.09) 0.025 V
ATTN (0.02-0.05) 0.047 V
OSC (0.01-0.04) 0.019 V
MIX (0.1-0.2) 0.042 V
BUF (1.5-2.0) 1.74 V
TR1 (0.5-1.0) 0.66 V
BPF (0.5-1.0) 0.78 V
TR2 (0.5-1.0) 0.72 V
TR3 (<0.01) 1.5 mV
DRV (0.9-1.6) 3.7 V
PA (10-15) 0 V
ANT (10-12) 0 V
RFD (1.7-2.0) 0 VDC
That was enough to convince me that it the the PA stage that is doing something wrong. I took the chance and cut Q7 out and it was indeed dead. I couldn’t measure any BE/BC resistance in any direction and the hfe was 0, too.
First I wanted to order replacements from Elecraft but the postage and Danish VAT would have made it 4 times as much as the price of the transistors. Instead I ordered two of them from the Danish El Supply together with some 1.5 and 2.0 amp fuses 😉
Unfortunately, El Supply did not have them on stock so I will have to wait about two weeks. Well, I can concentrate on other projects in the meantime.