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Author Topic: TS-830S did I wreck the finals?  (Read 989 times)
W4HGR
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Posts: 3




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« on: January 19, 2019, 05:06:16 AM »

New to me but used TS-830S traded for at a swapmeet.  Brought her home and learned to tune up and did a QSO or two.  Seemed to work fine, tuned up as expected, loading and power output okay.

Then, had a problem and found out the microphone that came with the radio had an intermittent short in the PTT line.  So the radio went several minutes transmitting with the finals not tuned.

Now the radio won't load up.  As my experience with tube finals is limited, what did I destroy?  New pair of final tubes necessary?  New Driver tube? 

Any assistance would be appreciated. 

Cliff W4HGR
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VK6HP
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Posts: 504




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« Reply #1 on: January 19, 2019, 06:13:40 AM »

A few more details would be helpful in tracking down the problem.  For example, what transmit mode was set during the extended transmission? Was it full power or tune power? Can you peak the drive to the PA (by monitoring the ALC on the meter)?  Is the HT sitting at around 800V? Is there idle current of 50-60 mA showing when you key the transmitter in LSB or USB mode? What plate current do you see in tune and CW modes? Can you dip the plate current? Is there zero, or just low, output?
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W4HGR
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« Reply #2 on: January 19, 2019, 06:25:10 AM »

Thanks for the reply ---
For example, what transmit mode was set during the extended transmission?
---The spurious transmit occurred in both Tune and CW mode
Was it full power or tune power?
---This happened on several occasions in both Tune and Full Power
Can you peak the drive to the PA (by monitoring the ALC on the meter)?
---Now, intermittently, I can peak the drive, but most of the time, no output is shown in TUNE mode.
Is the HT sitting at around 800V?
---Yes
...
---Now, there is zero Plate Current, so no dip in CW mode
 Is there zero, or just low, output?
---Zero output now
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N8YX
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« Reply #3 on: January 19, 2019, 06:35:17 AM »

Zero plate current = cathode resistors likely burned out.

Open 'er up and get the service manual out, along with an ohmmeter.
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VK6HP
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Posts: 504




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« Reply #4 on: January 19, 2019, 06:48:37 AM »

Yes, I'd also start by having a good look at the PA tube voltages.  You may well find the cathode resistors open circuit, as the previous poster suggested.  In the event that the remaining tube electrode voltages (plate, screen, grid) are present and roughly correct, I'd substitute two known-good 6146Bs and go from there.  You need to establish correct PA dc operating conditions as a starting point.  Getting to the correct idle current is a good first aiming point. 
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VA6JRC
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« Reply #5 on: January 19, 2019, 08:34:57 AM »

Yes as mentioned,with no plate current you will want to check the cathode resistors. There are 4, 20 ohm resistors ( 1/2 watt each) , for a total of 5 ohms. You will find them on the bottom of the Finals PC board just below the PA tubes. As I recall, they are designed to function as a fuse if a current over load occurs.
 R2, R3, R4, and R5 on the schematic diagram.

Be sure to check that the high voltage has been discharged to ground. Normally the bleeder resistors will do this within a few minutes, but wise to check yourself.

Cheers
VA6JRC
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W4HGR
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« Reply #6 on: January 20, 2019, 11:05:42 AM »

Thanks, everyone for the ideas and suggestions.  I checked the cathode resistors and their DC resistance in parallel was 5.7 ohms.  On inspection, these did not look burnt or damaged in any way.
I did find a green wire on the finals board which takes heater voltage somewhere (probably the driver tube) that had been cut and poorly repaired - twisted together and taped.  It fell apart as I was looking at it so the heater voltage to the driver was probably intermittent.  Some solder and heat shrink fixed that and the radio is back to normal operation.
Again, thank you!  Great forum - 73 / Cliff W4HGR
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VA6JRC
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« Reply #7 on: January 20, 2019, 11:56:46 AM »

Sometimes trouble shooting just involves having a good look at the pc boards and the wiring. That wire you repaired was likely the power feeding the 6146 filaments.
The 830S is a great radio, and I like mine a lot. I use it now on FT8 and it does a fine job.
Cheers
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KB4MNG
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Posts: 350




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« Reply #8 on: January 20, 2019, 06:21:02 PM »

Extended transmit in a non tune status is really bad. Not telling what damage has occurred. I did a full cw key down for over 30min on a TS 520 by accident. I thought I had done damage but it did not cause any issues. i was lucky.
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