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Old 9th Feb 2019, 4:06 am   #1
G8UWM-MildMartin
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Default Kenwood TS-520SE Transceiver overhaul notes Pt1

I recently obtained a Kenwood TS-520SE HF Transceiver.
I nearly had kittens on receipt of a parcel of dimensions similar to the published size of the equipment!
On unpacking, the only damage was to the underside of the case, which was easy enough to hammer back into shape.
Whilst the case was off, I noticed it had the optional CW filter
I decided to check the HT electrolytics. They were not charged, and showed good for capacitance and ESR, with parallel resistance into the megohms.
Strange, as they have 470-K bleeders!
They were O/C, as were the ones across the rectifiers and another one across some other electrolytics.
They were carbon composition 0.5-W. Not ideal for having 450V across them for nearly 4 decades!
I replaced them with: RS Stock No. 683-5290 Vishay Part No. VR37000004703JA100 rated at 3.5kV 0.5W.
The VFO tuning drive was lumpy, so I removed the VFO and cleaned and lubricated it, replaced the (all) dead lamps with new (eBay item 253857115964, removing supplied leads and joining to existing wires with heat-shrink) and cleaned the front panel and knobs while they were removed.
It is now fully functional on receive, and the quiescent current and HT voltage on transmit are correct.

Part 2 may follow once I have a suitable dummy load.
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Old 9th Feb 2019, 6:51 pm   #2
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Default Re: Kenwood TS-520SE Transceiver overhaul notes Pt1

Sounding good so far.
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Old 9th Feb 2019, 7:06 pm   #3
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Default Re: Kenwood TS-520SE Transceiver overhaul notes Pt1

Interesting! I have a 530, so lessons learned could well apply there.

For a while, I was tempted to let it go, but it's one of last "proper radios" with knobs instead of buttons, and I've decided to keep it.

Best of luck with your 520.

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Old 9th Feb 2019, 7:39 pm   #4
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Default Re: Kenwood TS-520SE Transceiver overhaul notes Pt1

I would keep it and use it.
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Old 9th Feb 2019, 8:59 pm   #5
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Default Re: Kenwood TS-520SE Transceiver overhaul notes Pt1

Yes, thinking about it, it hasn't been powered up for a while. I'll dig it of its cupboard and hook it to the Variac .

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Old 9th Feb 2019, 9:54 pm   #6
G8UWM-MildMartin
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Default Re: Kenwood TS-520SE Transceiver overhaul notes Pt1

Thanks.
A quick look at the TS-530S service manual online has a photo showing the same type of resistors across the big electrolytics, and possibly on the rectifier PCB, but obscured by wires.
Since these are equalising resistors across the capacitors and diodes, failure of one would subject its component to overvoltage. As carbon composition resistors are notorious for failing even when unused, I'd definitely suggest checking them before powering up!
I trust your 530 has survived even better than my 520.
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Old 9th Feb 2019, 10:22 pm   #7
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Default Re: Kenwood TS-520SE Transceiver overhaul notes Pt1

Thanks for that info, but I'd actually powered it up before seeing your post (at least as far as the Rx and Heaters, so that would have put the HT on also). But, it did power up OK and seems to be working on the Rx side, though some Servisol might be beneficial.

I'll add checking (replacing) those resistors on the "To Do List".

I cannot remember when I bought it (many years ago), but it was secondhand from one of the big ham radio dealers. Seemed fairly good and had what looked like brand new GE 6146's in the PA, which tested very well indeed.

I see there's a Yahoo group for the 520/30 and 820/30, so I've just subscribed to that.

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Old 9th Feb 2019, 10:34 pm   #8
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Default Re: Kenwood TS-520SE Transceiver overhaul notes Pt1

Thanks for info. on the Yahoo group. I've just applied to join.
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Old 9th Feb 2019, 10:59 pm   #9
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Default Re: Kenwood TS-520SE Transceiver overhaul notes Pt1

I just looked at the circuit diagram for those 6 off 470k resistors. Considering that the very nice Vishay resistors you've suggested are ~1p each, that looks like a very wise move; keep them coming .

Re the VFO, is that a simple air-spaced cap that does the tuning? I notice that the digital readout dropped out a couple of times at certain specific locations in the tuning range, hence the Servisol comment. That's happened since its been in storage.

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Old 10th Feb 2019, 3:14 am   #10
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Default Re: Kenwood TS-520SE Transceiver overhaul notes Pt1

Yes, it's a proper air-spaced capacitor with ceramic ends (in the 520, anyway).
The VFO isn't *very* easy to remove, needing the front panel and the PCBs behind and in front and a couple of "freezer bag ties" on the harness to be loosened and moved (at which stage the lamps are accessible) but it's OK, working methodically with the service manual, and there are some Youtube videos that give an overview ("Kenwood TS520" and "Kenwood VFO")( https://www.google.com/url?sa=t&rct=...9nAyIcQk0RPdVi, https://www.google.com/url?sa=t&rct=...c1SN3kjn--ePH8 although I don't necessarily agree with the rough treatment in the one that de-soldered the back wiper...
And another covered dismantling the gearbox, risking removing his fingers with an electric drill, then omitting how to re-tension the split (anti-backlash) gears on re-assembly.
They do mention the grease on the ball-bearings on the capacitor and the planetary drive hardening with age, though.
And they're very useful complements to the service manual, nonetheless.

Last edited by G8UWM-MildMartin; 10th Feb 2019 at 3:19 am.
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Old 10th Feb 2019, 7:19 pm   #11
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Default Re: Kenwood TS-520SE Transceiver overhaul notes Pt1

Thanks for that info. My VFO feels fine when tuned, but looks like there may be contact problems when the VC is close to either end of the range. Wonder what lube you used on it?

Back to the Rectifier Brd, part X43-1370-02 for the 530, coming off the 800V line is a line designated as 'HV' with R5,6&7 in direct series, each one being a 680k resistor. I haven't managed to find those in the parts list . I wonder if they too are composite resistors which may warrant attention?

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Old 11th Feb 2019, 1:29 am   #12
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Default Re: Kenwood TS-520SE Transceiver overhaul notes Pt1

I used the usual Servisol Super 10 for the contact spring, also to loosen and flush out the grease, then lithium-based grease for the rear ball bearing, front balls and epicyclic drive balls and shaft.
The 680-K (your R5,6&7, my R2,3,4) appeared to be carbon film, but the associated 100K was carbon composition. I de-soldered one end of R6 to measure them all: they were all just high of their 5% tolerance, but within 10%. Work had stock of suitable 0.75-W 1% resistors, not used on any current product, so I changed them while the board was loose and the desoldering machine was on. It made no noticeable difference to the meter reading on "HV" in TX, so I didn't mention it earlier.
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