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eHam Forums => Boat Anchors => Topic started by: N6QWP on October 26, 2017, 08:29:28 PM



Title: TS-940 TR relay: can you hear it switching?
Post by: N6QWP on October 26, 2017, 08:29:28 PM
Having a problem with my TS-940 and not getting output.  If you have a 940, can you hear the TR relay when hitting the PPT on mic?  Transmit light (red) does indicate when in xmit.  

Have another thread started in Repair....but need to know if one can actually hear the TR relay clicking on a TS-940 when put in transmit?  Hoping that someone who is a 940 user can let me know if you can actually hear the relay when put into xmit??

An answer to that singular question will let me know if my problem is isolated to that relay....or another issue all together.


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: KC4ZGP on October 27, 2017, 07:22:40 AM

You don't hear relays? Never met a relay-quiet radio.

Might have to open 'er up and give a listen. If the transmit light is on and you
don't hear a relay, your finals might be suffering dumping their RF to nowhere.

I take it you're looking at the transceiver's meter. Have you tried an external meter?

Kraus





Title: RE: TS-940 TR relay: can you hear it switching?
Post by: N6QWP on October 27, 2017, 07:47:16 AM
I previously posted that I could only get about 5 watts out on the meter in my external antenna tuner.  I measured 29 vdc to the finals both on the rigs meter and on a dvm.  That was the only voltage that I checked on final unit.

Will check to make sure that I also have 13 vdc on that board.  Any other voltages I should check for?  Anything else that could keep the final amp from working?  As I stated in my repair post, I replaced the entire final unit with the same results for lack of output.

I thought that I should be able to hear the TR relay,,,,,but do not.  If rely is not working, where will all that rf go?  As I said, no indication of IC or power out on rigs meter.

Other than relay failure, is there any other possible cause of these symptoms?

UPDATE! I am told that there is NO TR RELAY=940 is using diode switching for TX???  If that is the case, what else then, can cause the lack of amplification in the final unit (that has already been replaced)?


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: KC4ZGP on October 27, 2017, 10:52:34 AM

I don't own a TS-940.

29 volts eh. I say that's normal. To produce 250 watts, 28vdc devices are employed. My 300 watt
EB-27A uses a pair of MRF-421. They require 28vdc.

Bias voltage measured at the base should be .6vdc to .7vdc.

Lift the bases and check each transistor's rectifying properties.

Find way to measure input signal at the base. The finals could be faulty but still let the driver's
RF signal through to the meter.

Kraus


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: N6QWP on October 27, 2017, 12:21:31 PM
As I posted before, I just replaced the entire final unit with one that was working in another radio=I am still getting the exact same symptoms as before with original final unit.

That leads me to believe that the problem is on the rf board--or some peripheral supply circuit?  What and where is the question?

Looking for some advise from someone familiar with the TS-940.  I will be pulling plugs and reseating the rf board.....but still not focused on any singular cause.  I am hoping that someone who has worked on or has had a 940 can help to isolate the problem.

Can anyone familiar with the 940 and who has a schematic, please check for where any other measurable voltages should be on the final board?  I keep having a nagging feeling that it could be a problem of a supply voltage (other than the 29 vdc to finals) that might be the problem???  Anyone see where such an issue could keep a good final unit from functioning???


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: KM1H on October 28, 2017, 07:06:39 AM
The 940 relay is very quiet, and Ive owned mine since the mid 80's but havent experienced your problem.

Those radios are notorious for poor connections and soldering on the various connectors, pin and coax type. A tiny drop of DeOxit D-100 on pins and reseat several times takes care of the oxidation. Then wiggle connectors and solder when you have an intermittent.

It took me a few years to get mine fully reliable.

Carl


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: N6QWP on October 28, 2017, 08:24:51 AM
Carl--Can you clarify whether or not there is or is not a relay in the TR circuit--OR if rig uses PIN diode(s) for this function???  I am still waiting for a manual to arrive.

If there is a relay, wondering if one set of contacts could perform switching function on all but antenna switching?  Same question if using diode(s)???

I can visualize a failed TX antenna connection possibly giving these symptoms.

Other than that, I am searching for some problem (other than the final unit itself) that could keep the final unit from passing and amplifying a TX signal on through to the antenna jack.

Anyone else familiar with the 940 have any other thoughts?


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: WB8PFZ on October 28, 2017, 09:55:02 AM
What does the IC function of the meter read when transmitting?


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: N6QWP on October 28, 2017, 10:17:47 AM
Absolute zero IC on xmit.....NO other meter readings at all EXCEPT for 29 vdc VC to finals on xmit.

Seems to indicate that signal is stopping BEFORE the final unit???

Would not the fact that I can hear the xmit audio and get an extremely loud, clear signal on my other receiver even with no antenna=indicate that the xmit rf unit is working properly???

Once again, let trying to isolate what other cause could interfere here???


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: WB8PFZ on October 28, 2017, 10:37:26 AM
I would think you would see some current indication on the meter.


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: WB8PFZ on October 28, 2017, 10:38:36 AM
I hear NO relay in mine.


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: N6QWP on October 28, 2017, 10:44:47 AM
Thanx for info about not hearing relay (is it due to a lack thereof)?  

I was typing on top of previous reply about "thought there would be some IC".....there is NONE!

So, why???  What would or could cause a "working" final unit to have absolutely none?


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: WB8PFZ on October 28, 2017, 11:39:25 AM
Time to grab the schematic. Mike


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: N6QWP on October 28, 2017, 11:50:17 AM
Yup...but, in the meantime, only have one for the TS-930 (which has the same final amp board) but other boards, supply  and switching are different.  While waiting for a 940 manual, I thought I might get some help from someone more knowledgeable who has the 940 manual and who might come up with a cause/fix.

Anyone care to step up?  Thanx


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: WB8PFZ on October 28, 2017, 12:22:13 PM
Check for voltage on the collectors in the final?


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: KM1H on October 28, 2017, 06:04:08 PM
A small reed relay only, try keying it on CW as you will have a better chance of hearing it.


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: KM1H on October 30, 2017, 03:35:43 PM
Here is the Service Manual

http://www.radiomanual.info/schemi/TS940_serv.pdf

Relay RL 4 on the RF board right at the back panel..
Pages 12 and 90 are the most relavant


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: N6QWP on October 31, 2017, 02:48:29 PM
My hard copy of the Service Manual should arrive any day now.  With my eyesight, I will need a printed copy to be able to get details and follow schematics.  Looking forward to then....thanks to all that have taken the time to answer and post suggestions.  73


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: KM1H on October 31, 2017, 04:57:41 PM
Use the magnification key on your computer or in PDF, works for me.


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: N6QWP on November 04, 2017, 10:03:38 AM
OK.....confession time.  Manual arrived.....turns out that the problem (that was so obvious, that it was foolishly overlooked) was due to a power supply failure :-[ :-[

While the meter on the 940 still reads 28 vdc, the actual measured voltage coming out of the AVR is 40 vdc.  How the meter on rig can still read 28 vdc is still a mystery to me.  Was waiting for the service manual before seriously trying to troubleshoot the insides of the radio.  The lesson learned, is that nothing can be taken for granted!

My mission now, is to purchase the necessary parts to rebuild the power supply and AVR board.....then cross my fingers and hope that the drivers in one of the three final units that I have, survived the over voltages?  

Has anyone had positive results in such a failure (where the drivers survived) ???  I know that the drivers are the usual victims in such a scenario, but I am still hopeful--until I can get the supply working and test each unit individually.  Just would like to get input as to whether I am destined to find that this would just be wishful thinking?

PS-Aside from the fact that my earlier information was erroneous and misleading, the knowledgeable replies did give valuable information about problems with these radios and will be available to whoever might be searching for similar situations.  None of the informed knowledge that is offered in these forums is wasted.....and it is all very much appreciated.  My apologies to anyone who is upset with my obvious lack of expertise in my quest to get this venerable rig back on the air despite my increasingly pervasive "old timers" afflictions.


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: N6QWP on November 05, 2017, 02:52:05 PM
OK, OK......this is really going to irritate those who still have their complete faculties.  Just realized that my dvm was misreading=due to low internal battery voltage. 

LET'S REWIND!  THE VOLTAGE TO THE FINAL UNIT (OUT OF THE AVR) IS 29 VOLTS!

This indicates that the panel meter on the TS-940 IS CORRECT!  Actually reading about 28.8-28.9 vdc?  So, the original postings and problems ARE CORRECT.  THE PROBLEM IS NOT WITH THE POWER SUPPLY OR AVR BOARD.


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: N6QWP on November 07, 2017, 08:45:47 AM
Since the 29 vdc voltage to final unit is correct, still looking for cause of no rf getting into or out of the final unit.  Two possibles (I am wondering) might be: 1) lack of control voltage (for bias) getting to the final unit from the rf board ???  Or 2) either of relays RL3 or RL4 failing to make good contact on the rf board ???

The bias control voltage (shown on voltage diagram) indicates 0 volts at the rf board (no xmit voltage given).  However, at the final board (#1 jack?), if followed to the transistor that it goes to, xmit voltage shows 12 +/-.....(0 on rcv).

If I take a measurement at #1, shouldn't I get the 12 vdc/- on xmit (if working correctly) ???  If not, wouldn't this indicate the reason for no rf output on the final unit?  Or....is this voltage developed at the transistor and the voltage at #1 is so low (even when going hi or low) that it will not indicate there?  Looking for a way to test it at the plug-if possible.

Or....either of the relays....RL3 or RL4?


Title: RE: TS-940 TR relay: can you hear it switching?
Post by: N6QWP on November 25, 2017, 06:35:39 PM
The last posted questions still remain unanswered.

What, if the 28 vdc supply to the good final unit is correct, can prevent that unit from getting a signal  to, or from amplifying the signal from the RF unit???  Again, have tried another working final unit with the same negative results.

What can be the "broken link" in the RF feed to final amp???  Can clearly hear the audio from the RF board in a closeby receiver.
 
What is the function and correct reading of the keying input voltage to the final unit???  (That can be read on a DVM at the final unit board)???

Am waiting for parts to replace the original power supply=before proceeding with testing, because of it's tendency to fail and cause catastrophic failures.....but would appreciate any clues to what could be the problem=if the RF board is working (at least to the last circuit on that board).....and the final unit is working properly in another rig, and the power supply's 28 vdc is correct to the unit???