Galaxy Saturn. Transmit Fault.

[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

[Superscope]

Finally found a decent quality Schematic.

It is the same Board (EPT 3600-14B) as found in the Galaxy DX 77.
Once I found the Board number, I was able to search for the
Board rather than the Rig.

Copy attached should anybody be looking for one.
I assume this isn't a Cybernet chassis after all?


Fault turned out to be a very strange Mod done by a previous owner.

The PTT ground line had been taken via the "Rec" Socket on the back.
So a Shorting Plug needs to be left plugged into the "Rec" socket or the
Mike doesn't Key.

Haven't got a clue why this would have been done, other than some
remote Tx operation maybe.


Ian

[Jon_G4MDC]

Sounds like the secret switch that stopped little jimmy starting the car...when ignition key switches were not much good and would turn with almost anything? (FS Keys!)

[merlinmaxwell]

Thanks for the second circuit diagram, I can spend ages perusing one of those. Note to self, Don't print this out on A3 at work, you will waste an evening...

I will see if my self discipline is good enough!

[Superscope]

This is a little bit off Tropic, but is directly connected (no pun intended)
to the original Fault.

I don't need the Mod which was done to the "REC" socket, so I would like
to put it back the way it should be.
If a feature is included on a Radio, it should work in my opinion regardless.

However, maybe I'm going Blind or something, but I just can't see mention of
the "REC" socket on either of the Schematics I have !

Can anybody tell me where the Central Pin of the "REC" RCA Socket
on the back connects back onto the Main Board (or elsewhere)?

Does anybody on the Forum actually have one of these Rigs?


Ian

[frsimen]

Ian

I don't have one of these, is REC a RECorder output maybe? If so, connect the centre to tag 48 on the PCB.

Paula

[trh01uk]

Originally Posted by Superscope

Fault turned out to be a very strange Mod done by a previous owner.

The PTT ground line had been taken via the "Rec" Socket on the back.
So a Shorting Plug needs to be left plugged into the "Rec" socket or the
Mike doesn't Key.

Haven't got a clue why this would have been done, other than some
remote Tx operation maybe.


Ian

Ian,

so many faults turn out to be "not as built" - i.e. not as it left the factory. Some demon hacker has been in there and altered things - for purposes that no-one can guess at. Of course, with this age of equipment, hacks are much harder to spot than with true vintage equipment, because usually it involves fitting (relatively) modern components, wire, etc in place of the originals, which then stand out a mile.

So I usually assume with some unknown bit of kit which is "faulty" - that it has to be checked for someone messing with it.....


Richard

[Dave757]

Hi Ian,

Full Service manual for this radio available on RigPix.

I wonder if the mod was done in earlier days when you might have had a 'visit'
so that you could demonstrate that the set was Receive Only by removing the plug when not in use.

Kind regards
Dave

[Superscope]

Ref post #6

Hi Paula,
Yes indeed it is a Record Socket.
It is supposed to output both the Rx and Tx Audio.

I will certainly try your suggestion.

Post #8

Thanks Dave,

I have the Service Manual, but it isn't that helpful.

Has the basic Tune up information, but not a great deal more.

Now that is an interesting idea about why the Mod may have been done.

Although, I imported this Rig from Italy, and I don't remember the
Italians ever having those kinds of problems!

Ian