??
Hi Dave,
Its been a while since I worked on
TRA931???s like well over 40 years ago now, but I do own
several TRA931???s and have had to maintain them from
time to time. The TRA931 was probably Racal???s
best-selling radio ever, literally thousands were made
and sold worldwide. They were designed as an export
radio using quality components to meeting MIL spec but
without all the paperwork and qualification that went
will producing a radio for NATO use. The TRA931 has and
still is used from the Artic/Antarctic to the jungles of
South America/Africa to the deserts of the Middle east.
It coped well win these environments and beat all its
competition on price and performance. The TRA931 was
produced from the early 1970???s until Racal was taken
over in 2000 and was a great seller for all this time.
Saying it was an export radio did not stop NATO
governments purchasing quantities of TRA931???s for
there own use so the radio proved to be a well liked and
requested radio worldwide.
??
Firstly, the TRA931 operates from a
nominal 24Vdc supply, typically you can go down to 18V
and even lower on receive and up to about 30Vdc. If you
go higher than 30V the 33v Zenner diode D3 mounted on
the main chassis will cause the 7A fuse FS1 to blow thus
protecting the radio from over voltage.
Secondly in the era when these sets
were made Tantalum capacitors where a new technology and
proved over the years not to be reliable. They will fail
for what appears to be no reason and I would recommend
you change them all in your radio if you can. I have
done this with my own TRA931. Depending on the age of
your TRA931 you may not have any tantalum capacitors at
all as the earlier TRA931???s did not have any tantalum
capacitors.
You need to find yourself a copy of
the TRA931 handbook (if you don???t already have one) so
you can access the schematic diagrams to make fault
finding somewhat easier. The VMARS website in the UK ()
has many Racal handbooks available to download but I am
not certain if you have to be a member to access the
manual section of the website.
You do not say if the fault is just
limited to Tx path or if you have problems on receive as
well? If the radio is receiving correctly a lot of the
common circuitry can be eliminated from your
fault-finding analysis. If your fault is common to both
Tx and Rx there are common areas like 1.4Mhz switching
where one should start one???s investigations.
When you say L16 went up in smoke
and C62 shorted I am assuming you are referring to the
Synthesiser board MA925? This issue being for example
C62 is not C62 for the radio but C62 just on the
Synthesiser board. When specifying a component or test
point, you also have to say what board it is from or
even if it???s a chassis component as the boards where
used in other products as well as the TRA931 so you can
have multiple references say to a R12 or TP11 in a
particular radio.
The only L16 I could find was on
the synthesiser board and assume the C62 was also as if
C62 shorted L16 would go up in smoke as you experienced.
The Synthesiser board has three outputs one at 1.4Mhz
(pins 61 & 62) one at 34Mhz (Pins 58 &59) and
the Main variable output (Pins 41 & 42) so it is
worth just checking they are all present before
continuing your fault finding further.
The TP1 you refer to on what board
is it? As the only TP1 I have found so far is on the
transceiver board and this is on the antenna side of the
channel mixer after the band pass filter?
Also what mode are you using when
you measure the power output? If you are measuring it in
???Tune??? I would have expected to see 4 to 6W output.
The PA board transistors often did
not have a connection to the ???collector pin??? as the
connection was made through the stud (also connected to
the collector) maybe someone else out there has
knowledge of this and will let you know.
Loosing the 1.4Mhz in the Tx path
on the Transceiver board can give you some of the
symptoms you are experiencing. There are multiple 1.4Mhz
switching points and PTT switching using 1N4149 diodes
which I have experienced problems with over the years. I
have had these simply just fail or more commonly exhibit
a high leakage current so you should exhibit some
suspicion of these diodes if they are located anywhere
near part of the circuit you are testing. You also need
to check the PTT switching as a 12V rail may be missing
and causing your issues there are multiple PSU regulator
circuits on each board so they all have to be checked as
functional before proceeding further with your
fault-finding.
??
I am sorry I cannot be of more help
in this email, I do hope you can find the fault as the
TRA931 is a radio worth saving and using.
Please let me know how you get on
with your investigations and I will be happy to help you
further and have email discussions with you to help you
fault find the radio.
??
Best regards
??
John G6LJU
-----Original
Message-----
From: Dave via groups.io
<kc3am@...>
To:
[email protected]
Sent: Sat, 11 Jul 2020 1:50
Subject: Re: [RacalRadio] just joined, need assistance
with a deaf Syncal 30
Hello John,
Dave here KC3AM and I am asking for some help. From
your comments above maybe you can help me some with my
TRA931 that I got from a friend who is now a SK.
Not knowing anything about this radio when I got it I
found out that I needed 24 VDC for power. I originally
powered it up from a 12 VDC supply and saw that it did
come to life and seemed to RX OK. I then tried it at
18 VDC and had about 4 watts RF out. I brought it up
to 23 VDC?? and all seemed well. Then the smoke came
out. In the power supply section. C 62 apparently
shorted and L16 went up in smoke. These were easy to
find since they were blackened. They have been exactly
replaced. 5, 9, 15 VDC all seem to be fine now but I
have very little RF out now, not my 4 watts. (This is
where I found another problem. On the PA board TR2 is
has the collector lead missing which is probably one
reason for the low initial output.) I cannot get my
initial 4 watts output now. Hooking the 3 - 30 BNC
jack to a Motorola service monitor I do see an output
signal exactly on frequency so the synth board is OK
and at TP1 I have the 8 MHz signal that matches the
front panel setting. I am using an old Motorola RF
voltmeter to look for RF. AT TP1 I have about 1/10
VDC. At the output of the wideband amp at A21 I have
about the same. Looking at the static voltage chart TR
33 & 32 look OK, TR31 I start with 24 VDC and only
drops to 20VDC upon transmit on the collector. TR31
looks OK but I am planning on replacing it anyway. All
voltages that I have looked at seem to be OK, 12TX
,24PA.
Can you offer any suggestions?
Thank you very much for your time.
Dave KC3AM
