I have been trying to repair the single and multi-tone (3 tones) roger beep feature (known as Extended Transmission Signal (ETS) on the mic) on a newly acquired Astatic EchoMax 2000. I found that both relays (K1 and K2) were not switching at all, so I replaced both but the fault persists. With ETS enabled on the mic, the momentary and latching PTT buttons (SW1 and SW2 respectively) both fail to produce a single or the proper multi-tone after de-keying. So, no single tone at all but the multi-tone just about manages to produce a very rapid two or may be three tone beep before the transmit ends.
This seems to me to be possibly a timing issue as I can get both ETS single and multi tones tones to work perfectly if I pre-short out the Transmit (pin 3, JP2) of the the RJ12 connector to ground (Gnd, JP2), so that the transceiver is already in transmit before either PTT button is pressed.
I wonder if someone might be able to advise me on how the timing at the end of transmission is handled and the components involved? Perhaps a capacitor has drifted out of tolerance, which is causing the time allowed for the roger beep to be shortened?
It's got a micro-processor in it (presumably it's a really old device?), so I would imagine all the timing, tone generation, etc. is all done inside that.
I believe it was last manufactured around 2009 and, yes, it uses a Zilog Z8 CMOS OTP MCU, but that appears to be functioning normally since it executes the single and multi roger beeps while already in Tx mode. I could be wrong but I suspect something else is either mis-sensing or interfering with the end-of-transmission period in which the roger beep is supposed to "play".
Seeing that the relays were faulty (bad contacts?) the next thing I would do is dose both switches with a good contact cleaner such as deoxit, or 3-in-1 oil.
If the relay contacts were oxidised or corroded to the point of not working, the switches may be too!
The coil on one relay was open circuit and there was no continuity between the common contacts and the n/o contacts on the other relay when its coil was energised. I suspect a previous owner may have used a 13.8V DC or greater supply voltage at some point, but there are no other functional signs that the mic suffered further damage, assuming this caused the relays to fail.
I took care of the the SW1 and SW2 4-pole-DT clean-up and test as a first step. All the pins that should make contact with each other in the off and on states do so successfully. It's a real mystery what is wrong.
I should mention that the mic runs off a 9V battery, but, with the appropriate battery connector, can be run off the included 9V power pack supply, which I don't have.