Author Topic: project ts-820s with hearing problems  (Read 8389 times)

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Offline KE0ITRTopic starter

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project ts-820s with hearing problems
« on: May 06, 2016, 02:27:29 am »
I recently purchased a kenwood TS-820S with the intention of repairing it (and learning a ton in the process) and I have come across a problem that Im stuck on.

Issues (updated as project progresses):

The unit is almost completely deaf. static can still be heard. (Fixed, Q2 of RF board replaced with NTE222)

DG-1 operation is intermittent (fixed, dirty contacts) and completely non functional at 7 mhz and below (fixed, open inductor L12 on X54-1150-00)
Antenna transformer L8 on coil pack shorted out between primary and secondary (fixed, transformer rewound)
VFO signal disappears when tuned above 400 (VFO taken apart and cleaned, problem disappeared)
ANT and RL-1 relays randomly and intermittently cycle on (fixed, AF-AVR board had been worked on some time in the past. Bad soldering, lifted traces, etc. I replaced the AF-AVR board with a new, known good unit)
S-meter is non functional in receive. probably related to how deaf the unit is. (Fixed, Q2 of RF board replaced with NTE222)
Dead bands (probably bandswitch related) on 3.5, 7, 14, 21 mhz as well as wwv (fixed, coil pack removed, switch wafers desoldered, contacts cleaned, resoldered.)
Physical damage shows on HV caps - (Fixed, HV caps replaced.)
Finals are missing (replacements installed, 6146B)
No ALC meter reading (fixed, improper alignment of bandswitch inside final cage)
plastic band switch coupler is badly cracked, nearly in half (on order)


The issue I am struggling with now is the unit is VERY deaf. (ATT is OFF) I can barely pick up the 25khz calibrator signal on the higher bands, and not at all on the lower bands. Tuning into the calibrator signal shows no indication on the S-meter. RF-GAIN is fully clockwise as well as AF-gain. Driver tube is installed. VFO shorting plug is installed. For good measure, I also soldered a jumper on the back of the external VFO connector between pins 8 and 9 for troubleshooting. all connectors have been disconnected, cleaned, and sprayed with deoxit before reconnecting.

I thought I had it when I found the antenna transformer (L8 on coil pack) shorted out, but issues persist. I dont have an RF signal generator at home to apply a signal to the antenna jack and measure just how deaf the unit is, haven't gotten time to take it in to my work and use the one there.

I dont currently own an RF Milivoltmeter or RF VTVM but I am looking to get those soon.

Does anyone here have any experience with these units? I'm convinced there's something simple I am missing.

Im going to take it to the local club meeting saturday as word has it one of the elmers here has lots of experience with kenwood hybrids. Ill post updates here as the project progresses.

Any guidance greatly appreciated!
« Last Edit: May 22, 2016, 07:44:09 pm by KE0ITR »
 

Offline Fank1

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Re: project ts-820s with hearing problems
« Reply #1 on: May 06, 2016, 10:03:28 pm »
The shorted xmfr may indicate lightning.
I would check the RF amplifier transistor first.
 
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Offline KE0ITRTopic starter

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Re: project ts-820s with hearing problems
« Reply #2 on: May 07, 2016, 01:42:54 am »
Checked Q2 on the RF board- PN 3SK35 (dual gate mosfet) and it appears to be dead, shorted between G1, S, and D (about 14 ohms)

Going to replace it with an NTE222

Thanks Fank1!
 

Offline KE0ITRTopic starter

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Re: project ts-820s with hearing problems
« Reply #3 on: May 14, 2016, 10:24:24 pm »
Q2 replaced, the radio is no longer deaf! NTE222 was a direct drop in fit.
S-meter now functions properly. Calibrator signal loud and clear.

Radio still goes silent on 7, 14, 21 and WWV. I believe it to be a band switch problem. Allready had the coil pack out too... should have checked it then.

Caps on the relay board replaced. Didnt like the look of them. (I sitll lack a proper capacitor leakage test set. Looking at ordering one of the cool "magic eye" ones, even though I know that means another project)

HV caps require replacement. I have no doubt their leaking, and they appear to be damaged physically from the bottom. I will not be installing the finals until these are replaced.

RF milivoltmeter (boonton 92b W/probe  ;D) is in the mail, recently purchased a VTVM (along with NOS tubes, and new manufacture caps). Hopefully by the time I work out all the bugs and replace the remaining bad components, Ill have everything to do the alignment procedures.

also acquired NOS 6146 tubes but I will not install them untill the HV caps are replaced. I need to run down to one of the elmers tube testers to get some matched.

Thanks again for your guidance Frank1. Ill keep posting updates as the project progresses. I suppose a few pictures are due
 

Offline AF6LJ

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Re: project ts-820s with hearing problems
« Reply #4 on: May 14, 2016, 10:49:43 pm »
http://www.hybridrestore.com/parts/
May be of some help

I have a TS-820 sounds like your's took a lightning hit.
You are most of the way there.
Sue AF6LJ
 

Offline KE0ITRTopic starter

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Re: project ts-820s with hearing problems
« Reply #5 on: May 16, 2016, 04:24:34 pm »
Small update:

All bands working correctly now. Removed coil pack, desoldered each switch wafer, and cleaned and checked all contacts for continuity.

LSB sounds tinny. Still waiting on equipment to arrive in order to perform the full alignment. I had checked the LSB setting in the past using my counter and it was dead on, not sure what happened.

USB sounds great. Decoded contacts from Brazil on JT65 (I live in North Dakota), with a less than ideal dipole antenna. Seems to out perform my Yaesu FRG-8800.

HV caps appear to be damaged on the bottom, the replacements are in the mail. Ive heard that these old ones have a tendency to detonate when they've had enough.

the receiver section seems to be complete. Going on vacation soon and wont be able to work on the transmit section until around this time next month.
 

Offline AF6LJ

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Re: project ts-820s with hearing problems
« Reply #6 on: May 17, 2016, 12:42:17 am »
Yes they will blow up on you if left long enough.
My TS-820 has good caps, the radio has not seen any abuse but needs some TLC.
Sue AF6LJ
 

Offline linux-works

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Re: project ts-820s with hearing problems
« Reply #7 on: May 17, 2016, 12:50:34 am »
wow, that was a radio from my time (I was active in the 70's and early 80's).  I had the odd ts-511s, which I think was not a US model; the 520 was more common and also this 820.

nice rig.  has all those glorious knobs and buttons.  not a touch screen to be found (lol).

Offline KE0ITRTopic starter

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Re: project ts-820s with hearing problems
« Reply #8 on: May 21, 2016, 03:11:25 am »
Update:

The HV caps have arrived and have been replaced. Finals installed.

A fellow ham at my work allowed me to borrow his dummy load today (an ameritron adl-1500, complete and total overkill for this project. nice unit though.) I hooked it up to the radio to test the transmit section, and to no surprise it has some issues.

Not knowing what a previous owner/technician may have done to the settings of the unit, I turned the bias knob at rear of the unit fully CCW. Fresh 6146 tubes were installed. The driver tube (which im in question of) came with the unit. All markings have been wiped off the driver. With screen grid voltage turned off I performed the neutralization procedure, but tuning the capacitor inside the final cage (I forget off the top of my head the number of it) seemed to have VERY little effect on my scope. Neutralization was performed with the dummy load hooked up, and with the scope set to measure AC at 5 mV/div, the antenna jack was probed from inside the final cage (I know this is dangerous. Precautions were taken.). I adjusted for minimum reading on the scope, but I suspect something is not right here, It seemed like I wasnt actually doing anything significant. There was maybe 1 mV of amplitude change across the full range of the capacitor. I am unsure if the finals or driver is to blame, I havent been able to get them tested yet. Finals were supposedly tested good, but haven't verified myself.

SG switch turned back on.

with the band switch on 10 meters and mode CW, I set the meter to measure the plate current and set the bias adjustment for 65 mA. Next up was ALC, which had a zero reading regardless of what I did. CAR was set to 12 o'clock, load full CCW, mode TUN. I think I have misaligned the plate knob's pointer when I removed the front face, as it is off the scale when the plates are fully meshed. Drive had no effect either. There is output at the antenna jack from the radio when it is switched to send (with dummy load attached) as indicated on my scope, albeit weak. Output at antenna jack was correct frequency for selected band.

I also removed both relays and cleaned them thoroughly. I figured it was worth a shot at dumb luck.

At this point I am calling the tubes into question, as the neutralization seemed to accomplish absolutely nothing. Going to the local radio club tomorrow to seek the wisdom of the elmers.

Another thing that occurred to me is that the cracked bandswitch coupler may be aggravating this problem. It is currently psudo-working, but it needs replaced badly. I am worried it may have slipped on the shaft on the side that is cracked, which goes to a rotary switch inside the final cage.

TL:DR; New problems:  ALC no indication, plate tuning indicator misaligned, band switch inside final cage likely misaligned, and Im probably doing something incorrectly during neutralization
 

Offline AF6LJ

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Re: project ts-820s with hearing problems
« Reply #9 on: May 21, 2016, 03:49:15 am »
The bandswitch misalignment will be easy to spot. For ten meters the last tap on the PA tank coil must be selected. A new shaft coupling is available and might be in order before going further.
Your 12BY7 (Driver tube) should be able to deliver at least 70V P to P to the grids of the 6146Bs on 3.5MHZ. And that much on 28MHZ minimum.

In those radios the weakness is the 12BY7 driver tube. Even though Kenwood exceeds the rated plate voltage on the 6146Bs they are hard to ruin.

The good news is you are most of the way there.  :-+ :-+
Sue AF6LJ
 
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Offline KE0ITRTopic starter

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Re: project ts-820s with hearing problems
« Reply #10 on: May 21, 2016, 11:24:44 pm »
Thanks for the advice Sue, but I have a silly question for ya. For 10 meters, is the last tap on the PA tank coil the top or bottom tap?

Thanks!
 

Offline AF6LJ

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Re: project ts-820s with hearing problems
« Reply #11 on: May 22, 2016, 02:17:56 pm »
Thanks for the advice Sue, but I have a silly question for ya. For 10 meters, is the last tap on the PA tank coil the top or bottom tap?

Thanks!


Going from memory it should be top tap...
Sue AF6LJ
 

Offline KE0ITRTopic starter

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Re: project ts-820s with hearing problems
« Reply #12 on: May 22, 2016, 07:42:35 pm »
Thanks again for the all the advice sue!

I figured out the neutralization of the finals. I do not currently have a watt meter to put in line with the dummy load. Dipping and loading is a new experience to me, but I am getting faster at it. The pointer for the plate adjustment is now properly lined up.

was able to see the output on my spectrum analyzer, correct frequency. I was able to verify output further by hooking up my antenna and flipping send on 28.300 mhz, a local ham about 20 miles from me was able to hear the cw. (improper antenna, under terrible band conditions)

The radio still needs a proper alignment. Still waiting on my new Boonton 92B to arrive.
 

Offline AF6LJ

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Re: project ts-820s with hearing problems
« Reply #13 on: May 22, 2016, 07:53:00 pm »
Good deal...
Always glad to help out.
Sue AF6LJ
 


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