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Author Topic: SG239 failure  (Read 1132 times)
9H1FQ
Member

Posts: 174




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« on: November 09, 2017, 04:23:28 PM »

My SG239 has failed!

On switch DC  on, auto LED. on, one relay click

With an ordinary lamp as dummy( as suggested in the manual)
dc on-
Tx key down
ALL  the BITES LEDs on
the lamp, momentarily full brightness
then, a relay click
and the lamp, dims
no further relay clicks- does not try to tune the lamp

The tuner was feeding a 300 ohm ribbon cable to a 40 m loop, which worked efficiently on all bands, except top. But, is it a coincedence, that I have tuned the loop , successfully  on 80 m- then changed to 20m - but, as I came back on 80m, the tuner failed!

Microprocessor?
where shall I start?
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An unknown gem of the Mediterranean sea is the Island of Malta. blessed with warm sun , all year round.
In just one day, you can see places which will make you travel in history from the Prehistoric temples throu the middle ages, the Knights of Malta, all the way to world war two. All the major civ
WB6BYU
Member

Posts: 17049




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« Reply #1 on: November 09, 2017, 05:36:58 PM »

How long is your 300 ohm ribbon cable?

A 40m loop tuned on 80m is a pretty difficult load:  very high impedance, and high
reactance when just off resonance.  This is the sort of impedance that most autotuner
manufacturers warn you not to try to match because the voltages can be very
high, and the relay contacts can arc together.

Depending on the length (and the losses) of the ribbon cable, the load may be
moderated somewhat, or possibly inverted so it has high currents instead.

The most common failure mode I've seen in such cases is that one (or more) sets of
relay contacts have welded themselves closed due to an arc across them, but often
that can result in the tuner cycling as it tries to find a match that it can't accomplish
because one of the coil steps is not available.  That depends on the specifics of the
tuner logic, however:  it might try to switch in a section of coil, find it didn't make any
difference, and give up because its algorithm for calculating the match setting returned
a bad number.

If you're lucky, dropping the tuner on the floor a few times might shake the contacts
free, but don't count on it being able to match the antenna on 80m without the contacts
sticking again.
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9H1FQ
Member

Posts: 174




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« Reply #2 on: November 10, 2017, 01:08:57 AM »

yes, you are probably right. But, I prefere to check the relays, connected directly to the antenna , by removing them , out of the pcb. There are also very high  voltage capacitors, which if shorted, the antenna is grounded.
Thanks for the idea.
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An unknown gem of the Mediterranean sea is the Island of Malta. blessed with warm sun , all year round.
In just one day, you can see places which will make you travel in history from the Prehistoric temples throu the middle ages, the Knights of Malta, all the way to world war two. All the major civ
KF4ZGZ
Member

Posts: 34


WWW

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« Reply #3 on: November 10, 2017, 02:48:39 AM »

The 239 is an awesome tuner. Fast, efficient.
And can survive anything except an internal static discharge.

These units had a problem with static discharges blowing the sense diode.
D3 I think.  Google and the internet will help.
It is surface mount .... too small for my old eyes.

It is reported that once the diode is out, it can be replace by the normal big one and work fine.

If you can push the manual button and hear relays click, then the problem is probably the diode.

 It will work manually but it is a MAJOR pita because of the massive number of relay configurations to go through to get a match.

Matt
 
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9H1FQ
Member

Posts: 174




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« Reply #4 on: November 10, 2017, 05:29:09 AM »

will check the diode too, great!
When doing troubleshooting, I like to gather as much info as I can, before getting down on the job.
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An unknown gem of the Mediterranean sea is the Island of Malta. blessed with warm sun , all year round.
In just one day, you can see places which will make you travel in history from the Prehistoric temples throu the middle ages, the Knights of Malta, all the way to world war two. All the major civ
KM1H
Member

Posts: 2465




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« Reply #5 on: November 10, 2017, 11:35:02 AM »

Is there anyone in the US that can repair the 239?

Carl
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9H1FQ
Member

Posts: 174




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« Reply #6 on: November 10, 2017, 11:49:24 PM »

All relays open and easily checked, without removing them. All seem ok.
The 20kv capacitors seem ok, altough may fail during operation!
All diodes around the three RF xformers seem ok

this is the who,e story I ve sent to SCG, with no acknowledgment or reply.
MY LAST BUY OF SCG  STUFF


“Installation:  Kenwood Transcuever  TS850S - 10 feet of 50 ohms coax to roof- SG239 feeding 29 feet of 300 ohms ribbon cable, to a 140 feet loop.

 SWR varied from 1:1 to 1:2  on  all bands from 40 m to 10m

Recently, I managed to tune this loop on 80 m, and gave me an almost 1:1 match. Changed frequency to 20m, got  1:2 , but, when I changed back to 80m, I couldnt get any decent swr, struggling to find proper tune.

At one point, I  cannot remember when, I could get the usual low swr on transmit on any frequency, ( not sure on 80m)  but, I could not hear any signals on recieve on any band.

Troubleshooting;

The situation now, using a lamp as a dummy load:

Switch DC power on, ( with no RF in, switch on auto )  one relay click- auto LED on
With about  50 watts RF in- all BITES  LEDs light up, and stay on - dummy  lamp, momentarily  at full brightness - then a single relay click- and the dummy lamp dims, but still some low   light.

Reset button, but, nothing changes.

Some relays have visible  contacts and could  not see any welded contacts.
Capacitors  C21/73/74/75 seem to be ok, unless they leak on load.
Relay contacts of K16 to K21 tested open

The schematic shows A1 diode  ring modulator ADE-1 as having 8 pins, when actually, there are only six pins.
The schematic shows the input at pin 1  and 8, when pin 1 is ground on the specification sheet, and pin 8 does not exist!

Can you help please? “




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An unknown gem of the Mediterranean sea is the Island of Malta. blessed with warm sun , all year round.
In just one day, you can see places which will make you travel in history from the Prehistoric temples throu the middle ages, the Knights of Malta, all the way to world war two. All the major civ
KF4ZGZ
Member

Posts: 34


WWW

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« Reply #7 on: November 11, 2017, 03:45:56 AM »

I just pulled my long dead 239 out and looked at it.
I actually made notes on the inside cover.
"d5 & d6 - sensing diodes ... located below the small yellow wound toroid"
"d= 1N914"

Does it work in manual? If so, it's probably the diodes.

Did you check the fuse?

Good Luck!  SGC ignored my emails also.

I've been trying to someone local just to replace the diodes . ( my eyes are too old for the tiny stuff)
No luck ......

Matt
« Last Edit: November 11, 2017, 03:55:17 AM by KF4ZGZ » Logged
AC2RY
Member

Posts: 278




Ignore
« Reply #8 on: November 11, 2017, 08:48:55 AM »

All relays open and easily checked, without removing them. All seem ok.
The 20kv capacitors seem ok, altough may fail during operation!
All diodes around the three RF xformers seem ok

this is the who,e story I ve sent to SCG, with no acknowledgment or reply.
MY LAST BUY OF SCG  STUFF


“Installation:  Kenwood Transcuever  TS850S - 10 feet of 50 ohms coax to roof- SG239 feeding 29 feet of 300 ohms ribbon cable, to a 140 feet loop.

 SWR varied from 1:1 to 1:2  on  all bands from 40 m to 10m

Recently, I managed to tune this loop on 80 m, and gave me an almost 1:1 match. Changed frequency to 20m, got  1:2 , but, when I changed back to 80m, I couldnt get any decent swr, struggling to find proper tune.

At one point, I  cannot remember when, I could get the usual low swr on transmit on any frequency, ( not sure on 80m)  but, I could not hear any signals on recieve on any band.

Troubleshooting;

The situation now, using a lamp as a dummy load:

Switch DC power on, ( with no RF in, switch on auto )  one relay click- auto LED on
With about  50 watts RF in- all BITES  LEDs light up, and stay on - dummy  lamp, momentarily  at full brightness - then a single relay click- and the dummy lamp dims, but still some low   light.

Reset button, but, nothing changes.

Some relays have visible  contacts and could  not see any welded contacts.
Capacitors  C21/73/74/75 seem to be ok, unless they leak on load.
Relay contacts of K16 to K21 tested open

The schematic shows A1 diode  ring modulator ADE-1 as having 8 pins, when actually, there are only six pins.
The schematic shows the input at pin 1  and 8, when pin 1 is ground on the specification sheet, and pin 8 does not exist!

Can you help please? “






Did you really tried to tune with 50W or more in? If you did, this was a direct cause of failure. Tuners like this one only need few watts to do do their job. That is why when leaving it in auto mode and changing frequencies, you need to send low power carrier first, and only when tune is completed, switch to full power (in this case up to 200W). If you send full power after changing frequency - it is only a matter of time when tuner will be fried.
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N7EKU
Member

Posts: 703




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« Reply #9 on: November 11, 2017, 03:50:19 PM »

Hi,

The one on the schematic looks like an SBL-1 (through-hole) and not an ADE-1 (smd).  Regardless, comparing the pinouts between the two mixers should help in tracing the circuit or replacing the mixer (if that is what is wrong).

Doing things like trying to tune a loop that is a half wave long, or a dipole at half its cut frequency or on an even harmonic of it, has probably ruined many tuners.  That's why it's not recommended to use automatic antenna tuners on very difficult loads like that.  Even doublets that happen to have unfortunate arm+ladderline lengths (ie. one didn't do any calculations to estimate the load facing the tuner) can do this.  It's not always the fault of the tuner, as there's not a lot that can be done to protect an auto tuner from the very high voltages that such loads can present.

From their website, it looks like SGC is in the middle of a move (after being in their old location for at least 35 years).   That's disappointing that they aren't keeping up with their email though.  Hopefully they get in touch with you when your tuner arrives.  Have you tried calling them on the telephone?  Hopefully that would work better.

73 and best of luck,


Mark.



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Mark -- N7EKU/VE3
9H1FQ
Member

Posts: 174




Ignore
« Reply #10 on: November 14, 2017, 12:27:27 AM »

Problem solved by ereasing the memory.
SGC are presently moving, thats why delay, or no reply.
Logged

An unknown gem of the Mediterranean sea is the Island of Malta. blessed with warm sun , all year round.
In just one day, you can see places which will make you travel in history from the Prehistoric temples throu the middle ages, the Knights of Malta, all the way to world war two. All the major civ
9H1FQ
Member

Posts: 174




Ignore
« Reply #11 on: November 14, 2017, 02:39:24 AM »

I just pulled my long dead 239 out and looked at it.
I actually made notes on the inside cover.
"d5 & d6 - sensing diodes ... located below the small yellow wound toroid"
"d= 1N914"

Does it work in manual? If so, it's probably the diodes.

Did you check the fuse?

Good Luck!  SGC ignored my emails also.

I've been trying to someone local just to replace the diodes . ( my eyes are too old for the tiny stuff)
No luck ......

Matt
Logged

An unknown gem of the Mediterranean sea is the Island of Malta. blessed with warm sun , all year round.
In just one day, you can see places which will make you travel in history from the Prehistoric temples throu the middle ages, the Knights of Malta, all the way to world war two. All the major civ
9H1FQ
Member

Posts: 174




Ignore
« Reply #12 on: November 14, 2017, 02:47:53 AM »

I just pulled my long dead 239 out and looked at it.
I actually made notes on the inside cover.
"d5 & d6 - sensing diodes ... located below the small yellow wound toroid"
"d= 1N914"

Does it work in manual? If so, it's probably the diodes.

Did you check the fuse?

Good Luck!  SGC ignored my emails also.






I have solved the problem by pressing the 2nd switch and the last switch , and apply dc power!
then wait, 10 minutes, and the tuner came alive. I had to do this procedure, 3 times!

So, its normal to find a dead short circuit on pins 2 and 3 on D5 and 6 at the input of ADE1 balanced modulator!  All the 6 pins should show gound, except pin 5, which should give a diode indication. The manual is showing an old version of the balanced modulator.

I could detect the 4.9mhz clock , using the oscilloscope. Strange, that I was unable to hear the beat on my TS850?.





I've been trying to someone local just to replace the diodes . ( my eyes are too old for the tiny stuff)
No luck ......

Matt
Logged

An unknown gem of the Mediterranean sea is the Island of Malta. blessed with warm sun , all year round.
In just one day, you can see places which will make you travel in history from the Prehistoric temples throu the middle ages, the Knights of Malta, all the way to world war two. All the major civ
9H1FQ
Member

Posts: 174




Ignore
« Reply #13 on: November 14, 2017, 02:49:23 AM »

Is there anyone in the US that can repair the 239?

Carl

I have contacted SGC . They are busy , moving their location.
Logged

An unknown gem of the Mediterranean sea is the Island of Malta. blessed with warm sun , all year round.
In just one day, you can see places which will make you travel in history from the Prehistoric temples throu the middle ages, the Knights of Malta, all the way to world war two. All the major civ
KM1H
Member

Posts: 2465




Ignore
« Reply #14 on: November 14, 2017, 02:58:54 PM »

Quote
An unknown gem of the Mediterranean sea is the Island of Malta. blessed with warm sun , all year round.
In just one day, you can see places which will make you travel in history from the Prehistoric temples throu the middle ages, the Knights of Malta, all the way to world war two. All the major civ

While in the USN on a couple of Med tours in the 60's I was fortunate enough to enjoy Maltese history, hospitality, and food. One small complement ship at a time was allowed and mine were a Fleet Oiler (tanker) and Refrigerated Food Ship (Reefer).
Those were my favorite stops of all the Med.

Carl
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