Electronics > RF, Microwave, Ham Radio

project ts-820s with hearing problems

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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!

The shorted xmfr may indicate lightning.
I would check the RF amplifier transistor first.

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!

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

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.


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