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Author Topic: TS-940 TR relay: can you hear it switching?  (Read 6828 times)
KM1H
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Posts: 2622




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« Reply #15 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.
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KM1H
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Posts: 2622




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« Reply #16 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
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N6QWP
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Posts: 259




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« Reply #17 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
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KM1H
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« Reply #18 on: October 31, 2017, 04:57:41 PM »

Use the magnification key on your computer or in PDF, works for me.
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N6QWP
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Posts: 259




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« Reply #19 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 Embarrassed Embarrassed

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) Huh  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.
« Last Edit: November 04, 2017, 10:25:34 AM by N6QWP » Logged
N6QWP
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Posts: 259




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« Reply #20 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.
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N6QWP
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Posts: 259




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« Reply #21 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 Huh  Or 2) either of relays RL3 or RL4 failing to make good contact on the rf board Huh

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) Huh  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?
« Last Edit: November 07, 2017, 09:05:52 AM by N6QWP » Logged
N6QWP
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Posts: 259




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« Reply #22 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)Huh

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???
« Last Edit: November 25, 2017, 06:44:24 PM by N6QWP » Logged
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