Fred McKenzie wrote:
In article . com,
wrote:

I have a TS-120 and I think the ears are a little weak, comparing the
rig with my 757, the s-meter on the 757 always reads more.

KJ4UO-

You shouldn't use the S-Meter to compare radios. S-Meters usually don't
tell the truth to begin with, and then some companies make their radios
read higher to make you think they are better.



73, Fred, K4DII

Fred - its irrelevant here - you are quite correct, but its irrelevant
in this context. The S meter on the ts120 shows different readings on
each band on its OWN cal. oscillator. This is what the oscillator is
designed to do (among other things)

Why make it more complicated than it has to be? - keep it simple. Gets
things done. Too much theory confuses the issue. Most techs earn a
living by doing the SIMPLE things.

And S-meter calibration standards - yes, they do exist for sure (and
they are, indeed, mildly interesting. If you have an accurate, in
calibration signal generator then you can check them.) - but what about
fixng the radio 1st, and THEN work out if the S-meter is properly
calibrated or not.

de VK3BFA Andrew

In article .com,
"Andrew VK3BFA" wrote:

Fred - its irrelevant here - you are quite correct, but its irrelevant
in this context. The S meter on the ts120 shows different readings on
each band on its OWN cal. oscillator. This is what the oscillator is
designed to do (among other things)

Andrew-

Perhaps I was a little off base. It has been a long time since I had a
TS-120S, and I don't recall the calibration oscillator. I loaned the
service manual to someone several years ago, so I can't check it out!

Since I wasn't aware of the utility of the calibration oscillator, the
only sure evidence of a malfunction was a reference to smoke that seemed
unrelated to receiver sensitivity.

For what it is worth, there is a service bulletin about replacing an input
RF transformer that might have been damaged by static discharge. I don't
know if it applies equally to the TS-120 and TS-120S.

73, Fred, K4DII

SB-040

TS-120S Ant Input Transformer Replacement 7-12-79

Ts-120S transceivers subject to strong static fields or similar high
current atmospheric discharges may suddenly exhibit low RX sensitivity on
all bands. TX will be OK. You may suspect T1 on the RF unit X44-1260-01.

When replacing or ordering T1, L43-0696-35, also check the value of C20.
If it is 33pF, just replace and repeak the transformer.

First production transceivers will have a 15pF cap for C20. When changing
T1, also replace C20 with a 33pF capacitor, and repeak the circuit.

Old part number: L34-0696-05 Antenna Coil
New part number: L34-0696-35
Old Capacitor was 15pF, replace with
New part number: CC45RH1H330J 33pf

Please make these changes in your service manual.

JEB/yn
(c) 71279TKC

Hi Fred,
yep - you are correct about the input transformers - they go open
circuit, and are a real ******* to replace, as you have to pull apart
the bandswitch mechanism, which usually generates its own set of nice
little problems.

I've done up 2 of them now - a nice little radio, and not too badly
made or designed, all things considered. Synthesiser is noisy, but hey,
its the technology of the time - and not as bad as some others of that
period! But can be really fiddly around the rf front end area. Things
like bandswitch wafers have run out as spare parts, most other things
are still available.

They are getting a bit old now, so have probably been through a few
owners - and if it has been "fiddled" with, can be a bugger to get all
the faults out - but usually worth the effort in the long run.

The CAL oscillator in any radio is also used as a crude signal
generator - so it gives a "quick and dirty" indication of where the
fault is - in this case, its as deaf as a post on 20m.

The loose wires around the bandswitch are a dead giveaway as well -
probably, someone has been in there in the past stuffing around. -
would look for a damaged switch contact as that might explain the loose
wires as well - someone was trying to fault find. Its unlikely to be
the input rx rf transformer as its common to all bands. The switch
wafers can USUALLY be brought back to life with some TLC - you need
more subtle tools than a big hammer, and the patience to do it tho.

73 de VK3BFA Andrew.

ps - this vintage radio is EMMINENTLY fixable at home - no custom VLSI
ics, common parts, simple design, reasonably accessible layout, NO SMD
"things"................ - if you can get a "good" one, go for it.


Fred McKenzie wrote:
In article .com,
"Andrew VK3BFA" wrote:

Fred - its irrelevant here - you are quite correct, but its irrelevant
in this context. The S meter on the ts120 shows different readings on
each band on its OWN cal. oscillator. This is what the oscillator is
designed to do (among other things)

Andrew-

Perhaps I was a little off base. It has been a long time since I had a
TS-120S, and I don't recall the calibration oscillator. I loaned the
service manual to someone several years ago, so I can't check it out!

Since I wasn't aware of the utility of the calibration oscillator, the
only sure evidence of a malfunction was a reference to smoke that seemed
unrelated to receiver sensitivity.

For what it is worth, there is a service bulletin about replacing an input
RF transformer that might have been damaged by static discharge. I don't
know if it applies equally to the TS-120 and TS-120S.

73, Fred, K4DII

Thanks all for discussing the post for my TS-120.

I had the radio open to torque down the band switch knob. For some
reason there was a wire that had been cut which had something to do
with the 15 MHz WWV/ JJY circuit.

The radio with the wire "cut" would draw about 15 amps in the WWV/JJY
switch while transmitting but would not put out any RF power. I did
not keep the key down very long, in fear that what ever was drawing the
current would be destroyed.

So I reconnected the wire and very little current is taken if the key
is pressed now on JJY. My thoughts is that someone was trying to get
the wwv/jjy switch to transmit as I can see on the schematic that is
wire disables one of the radio's RF sections. Maybe a possible mod to
get up to 18 MHz.

Since no power is radiated, there must be another tuned-circuit that
prevents any RF.

I was listening to the 20 meter band today, while the s-meter was not
giving the same signal strenght as a reference FT-757, the TS-120 could
copy every weak signal the 757 could.

Cheers, de KJ4UO

I was listening to the 20 meter band today, while the s-meter was not
giving the same signal strenght as a reference FT-757, the TS-120 could
copy every weak signal the 757 could.
=========================
If you want to increase the indication of the S-meter (for example because
you wish it to be the same as on your other transceiver) ,there highly
likely is a trimpot near the meter or in the associated AGC circuit which
you can manipulate. Almost every S-meter derives its signal from the AGC.
If you have a signal generator and a good quality attenuator you can set the
S-meter indication to S9 with a receiver input of 50 microvolts @ 50 Ohms
(-73dBm).
Of course it doesn't mean that the S-meter is then correct over its entire
scale ,
1 S-point meant to be a change of 6 dB.

Frank GM0CSZ / KN6WH

wrote:
Thanks all for discussing the post for my TS-120.

I had the radio open to torque down the band switch knob. For some
reason there was a wire that had been cut which had something to do
with the 15 MHz WWV/ JJY circuit.



I was listening to the 20 meter band today, while the s-meter was not
giving the same signal strenght as a reference FT-757, the TS-120 could
copy every weak signal the 757 could.

Cheers, de KJ4UO

Well, this is getting a bit too much to comprehend - from your original
post, the TS120 had a MDS (Minimum Discernable Signal) of -100dbm, ie
2.25uv - which is pretty poor. If your FT757 is getting the same
results, then its sick too - and it SHOULD be better considering the
high synthesiser noise in the TS120.

Why not read the specifications for your radios - and then post some
meaningful test figures.

73 de VK3BFA Andrew