[Superscope]

Can anybody help me with a Tx switching fault on a Galaxy Saturn Home Base Transceiver?

Also known as the Ham International Jumbo 2, or Midland Alan 555

Simple switching fault I thought!

A common fault with these Rigs apparently, is the Tx Switching Transistor TR38.

So I started there. EBC Voltages are correct for Rx, not surprisingly as Rx works fine.
On Tx, the collector Voltage doesn't change as it is supposed too on Tx, so one assumes it isn't switching.
However in circuit testing of the transistor junctions seem fine.

Bridging E and C together and the Rig fires up, so the fault one assumes is on TR38 or before.

But I can't get my Head around how the Switching works.
How does keying the Mike get round to switching this Transistor ?

I have studied the Schematic, which is small and difficult to read, which
doesn't help, but can't work out how the Mike switches this Transistor.

How does almost no change in Base Voltage between Rx and Tx allow the
Transistor to switch in the first place? (according to the Service Data).

I would rather try to understand properly how the Switching works, before I start
removing components for out of circuit testing.

I believe this is a Cybernet Chassis, but can't find any Board Number.

Are there any knowledgable Forum Members who are familiar with this Rig who
could explain how the switching works ?


Ian