TS-120
 

Hi all,

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.

The 120 has a cal signal knob, I put the cal signal out on 14.2 MHz and
get S-3, on the 21.2, it back up to S-7. The best output is at 29.2
with a little over S-9.

I don't understand why it takes a dip in the 20 meter and in the JJY
band, since JJY band is for WWV at 15 MHz just above the 20 meter band
then it would use some of the same circuits.

The lower bands, 80 meters is putting out the least.

I did see where a wire had been cut and this wire was touching just
behind the last waper on the RF board. It emitted smoke while
listening in the 20 meter band but not in the other bands.

As far as using a signal generator, I have a wavetek 3001, I could
determine a signal down to about -100dbm on 20 meters and down to about
-110 dbm on 15 meters.

I did not have any reference data before the event.

If you have a TS-120 and can look at 14.2 21.2 and the other bands as
the band switch is moved and tell me your reading, it may tell me if I
need to search for a defective part.

As far as I could tell, the unit still draws about 20 amps into the
dummy load so output power did not change.

De KJ4UO

Erk - hi all,

you need to get a very basic book on radios, and read up the theory -
it will improve your fault finding no end. (probably mid 70's ARRL
handbook would be a good primer)

The sig gen is irrelevant at this stage - you have already proved that
by observation of the S meter during Cal (thats one of its functions
along with calibrating frequency)

Also, unconnected wires and/or smoke are a basic radio no no.

This is going to be hard --- to try and fix a radio by remote
control, but will give it a try if you want to persevere.

73 de VK3BFA Andrew

-ex- wrote:
wrote:

Hi all,

I have a TS-120

The 120 has a cal signal knob, I put the cal signal out on 14.2 MHz and
get S-3, on the 21.2, it back up to S-7. The best output is at 29.2
with a little over S-9.

I don't understand why it takes a dip in the 20 meter and in the JJY
band, since JJY band is for WWV at 15 MHz just above the 20 meter band
then it would use some of the same circuits.

It emitted smoke while
listening in the 20 meter band but not in the other bands.

As far as using a signal generator, I have a wavetek 3001, I could
determine a signal down to about -100dbm on 20 meters and down to about
-110 dbm on 15 meters.

That "smoke" part is very indicative of something wrong and should be a
good lead for troubleshooting!

-BM

Andrew VK3BFA wrote:

Erk - hi all,

you need to get a very basic book on radios, and read up the theory -
it will improve your fault finding no end. (probably mid 70's ARRL
handbook would be a good primer)

The sig gen is irrelevant at this stage - you have already proved that
by observation of the S meter during Cal (thats one of its functions
along with calibrating frequency)

Also, unconnected wires and/or smoke are a basic radio no no.

This is going to be hard --- to try and fix a radio by remote
control, but will give it a try if you want to persevere.

73 de VK3BFA Andrew

I'm not so sure that any book would help with a specific model problem.
After all, the OP is a licensed ham wih a callsign and *should* be
savvy enough to look for where the smoke came from.
At this point of troubleshooting it would seem that OP would be equally
served with a book on "Olifactory Recognition" inasmuch as an
electronics book. One cannot simply read a 30 year old ARRL Handbook
and fix a complicated modern radio.

-Bill

-ex- wrote:
Andrew VK3BFA wrote:

Erk - hi all,

you need to get a very basic book on radios, and read up the theory -
it will improve your fault finding no end. (probably mid 70's ARRL
handbook would be a good primer)


I'm not so sure that any book would help with a specific model problem.
After all, the OP is a licensed ham wih a callsign and *should* be
savvy enough to look for where the smoke came from.
At this point of troubleshooting it would seem that OP would be equally
served with a book on "Olifactory Recognition" inasmuch as an
electronics book. One cannot simply read a 30 year old ARRL Handbook
and fix a complicated modern radio.

-Bill

Hi Bill,
no, the arrl book wont tell you how to fix a kenwood ts-120 - but it
will provide you with the basic theory of

1) how it works and
2) how to start logical fault finding.

Unless you have at least block level understanding of what is in front
of you, then you wont have ANY chance of fixing it.

Besides, by modern standards, the ts120 IS an old, simple radio, and
SHOULD be able to be serviced in the home workshop. You just need to
have enough basic radio theory to start working your way through. The
license qualification gets you on air - thats all. And most people
forget the theory unless it is subsequently applied in practice.

To me, at any rate, the 'fun' bit of AR is building and getting things
to work - I have no real interest in talking to people on air !

And RF is my field of interest - digital is a mystery, and am quite
content to ask for help and guidance if I have a problem.

73 de VK3BFA Andrew

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.

Somewhere it is written that a meter should read S-9 with 50 microvolts RF
input, and that for each S-Unit there should be a 6 dB change in RF
signal. You can check this with a calibrated signal generator. However
few radios will meet these specs and not everyone agrees with the values.
In other words, it isn't as much a "standard" as such things as the AC
voltage and frequency coming into your house.

To check the receiver's "ears", you need a calibrated signal generator to
find the lowest signal level it can receive. That is its sensitivity, and
that is what you should use to compare radios regardless of S-Meter
reading.

73, Fred, K4DII

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