Desktop Microphone Fault

[BlueYonder]

Hi,

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?

Thanks!

BY

 

[Nigel Goodwin]

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.

 

[BlueYonder]

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".

 

[rjenkinsgb]

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!

 

[BlueYonder]

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.

 

[BlueYonder]

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.

Thanks for your suggestions.