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Aging Issues With Past Century Kenwood Equipment

from Pedro M.J. Wyns ON7WP, AA9HX, C5WP on January 26, 2017
View comments about this article!

Aging Issues With Past Century Kenwood Equipment
by Pedro M.J. Wyns BE(T)

Being a ham for 35 years now, licensed at the age of 15, I am building up a collection of radios I loved to have in my novice era, because at that time I did not have the money to buy them, so it is kind of catching up behavior buying these beauties.

It is not only about collecting the radios to put them up on a stand, but it is about having them fully operational and with the intention of using them at regular intervals.

To keep everything within budget, and because it is kind of fun to me to repair radios (I see defective radios as kind of a puzzle), I often buy them on second hand sites and Hamfests, or silent key sales.

One can see funny things happening: did you know that on eBay a radio advertised as 'defective' or 'tech-special' as they call broken radios in the US gets a lot more bids and often a higher end price than a similar radio in 'good working condition?'

In this article I want to share some observations and mention some cures on often found issues with these older radios, in particular based on a practical example of a Kenwood TS-780 VHF-UHF flagship of the eighties. (1982 upwards). I bought the radio for 50, something like 75$ since Trump got elected :-) in a brand new exterior state, and never opened, so ideal to start faultfinding. Observations were no power output, receiver operational at some frequencies and virtually no output (micro watts).

I started by trying to decode why the receiver worked at some frequencies and not at others. After testing I found out it worked at the high end of each 20 kHz window. My first guess was a PLL loop adjustment issue with one of the synthesizer loops, as the circuit is built around two nested loops. This is a common problem in older radios. As VCO's tend to be 'immunized' against microphonics with kind of candle grease, this grease tends to attack components so resonant frequencies can move. Especially the TS-440 suffered from this problem. Apart from that, the colored plastic type of trimmer capacitor used often has issues with bad rotor contacts, resulting in aurora-like sounds or no lock at all. A lot of Icom radios of the eighties have this issue.

Always check first PLL voltages in the middle of the tuning range to start with. This TS-780 baby showed some deviation from the values announced in the service manual but never went out of lock (if you measure 0V or the supply voltage) at one of the ends of the dial tuning range. So I had to dig in deeper. To keep a long story short, and as this was a very difficult problem to trace, the culprit were the two ceramic 10.19 MHz filters used in one of the mixing loop amplifiers. I was aware of the famous filter pandemic in the Yaesu FT857-FT897 series that affected the Murata 455 kHz filters due to electro-mitigation based on a design issue that left DC on the filter ports, but I never experienced any issues with the capacitor-shaped Toko 3 pin IF filters.

Enclosed some pictures of the filters when swept in my network analyzer. At the low end of the 20 kHz PLL range the filter attenuated more than 20 dB so the loop did not work properly any more. The cure? Impossible to find new replacement 10.19 MHz filters, I guess they were custom made for this radio, so I needed another approach. Looking at the design I decided the filters were not really needed for this application so I replaced them by 100 nF capacitors (!). Maybe spectral purity suffered a bit but there was no other option left... And yes, the loop came back alive, radio operational on all frequencies. First problem solved, now I had a deaf radio that worked at all frequencies with no output, what a progress :-)

The next step was to determine why the radio had virtually no output. I spent a few afternoons checking all active devices in the TX path but none of them appeared to be defective. I also read horror stories about 2SC460 devices that had their Hfe degraded from 100 to 3, so I took no chances and de-soldered a few at random to check them in my Chinese component tester but all appeared OK. -- Dead end, but still no power. Then I remembered a curious case with a TS930 HF radio that had almost no output as well, due to a IF transformer with a purple core that was completely off spec. (Afterwards after publishing this repair mod document I got several mails from people all over the world that had the very same issue). So I started tracing the IF SSB generator path with my spectrum analyzer and soon found similar IF transformers with green and black cores that were completely off spec. After readjusting these cores the radio was back at normal power output and normal sensitivity.

The only issue left after some thorough testing was a slightly off spec SSB balanced modulator, with carrier leakage and some audio bandwidth issues. The fault a lot of people do to fix this is to readjust the carrier crystal oscillators to the value as specified in the service manual: wrong, o so wrong...

Not only the carrier crystals drift, also the SSB filter itself (based on similar crystals) is subjected to aging!

The only correct way to readjust the SSB modulator of an old radio is by using a dual tone generator, using 300 and 2500 Hz tones. The carrier crystals are then aligned in such a way that both tones have similar amplitudes when the radio's output signal is observed on a spectrum analyzer. This is repeated for both USB and LSB. (Poor man solution is alternatively apply each tone and observe watt meter readings using an audio drive signal below ALC action.)

When servicing old radios, always check the big electrolytic capacitors used in the power supply. Check the ripple or better test them with a (Chinese) ESR tester. Check also the capacitors on the supply lines of the power modules, often these die also and generator LF oscillations.

Also check the transformer primary settings. They were often sold in 220V era and now used on grids that are more close to 240V. Changing the transformer tap to 240V reliefs the load on the PSU and reduces the heat in the radio, often the cause of other failures. (110V to 120V for US based readers).

Last but not least to fix are the light bulbs used to illuminate the dial and meters. The best way to fix these is to replace these by LED-SMD chips that are physically hold in position by two serial current limiting resistors. Such solid state bulb replacement is due to live forever.

Summary: Not all malfunctions in radios are caused by defective active components. This is a clear case of a defective radio based on failures of two passive components: ceramic IF filters and ferrite core material in IF transformers.

I hope above tips encourage people to keep old radios operational, or motivate people to take another look at that defective radio in the basement. You can express your appreciation for this article by sending me some feedback email, or better use DHL to send me a crate of wine :-)





Pedro M.J. Wyns ON7WP, AA9HX, C5WP pedro.wyns @ gmail.com
Broadcast Consultant - Telecom Expert Radio Guru
Mechelsesteenweg 14
B-2220 Heist-op-den-Berg
Belgium - Europe

Member Comments:
Add A Comment
 
Aging Issues With Past Century Kenwood Equipment Reply
by N2UJN on January 27, 2017 Mail this to a friend!
Pedro,
Excellent article! Thank you for good analytical summary and the humorous and informative writing.

Regarding your noted preferred feedback - As they say here in the states: The case of wine is in the mail!

Mike
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by W8QZ on January 27, 2017 Mail this to a friend!
Nice bit of detective work, tracking that all down. Not all of us have the skills, tools, or time to do such, however. At least you didn't run into a show-stopper issue of a failed custom-to-Kenwood unobtainable IC - that has turned many modern radios into 'parts donors'.
 
Aging Issues With Past Century Kenwood Equipment Reply
by ON4AA on January 27, 2017 Mail this to a friend!
Proficiat met dit prachtig artikel!

73 de Serge, ON4AA
http://hamwaves.com/propagation/en/index.html
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by K9MHZ on January 27, 2017 Mail this to a friend!
Good work, Pedro. Glad you didn't have to dig through any wax on the tops of those cores.
 
Aging Issues With Past Century Kenwood Equipment Reply
by AB9TA on January 27, 2017 Mail this to a friend!
Excellent Article,
I wish we had a few more like this on the esteemed eHam website!

73!
Bill AB9TA
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by K6AER on January 27, 2017 Mail this to a friend!
I looked into the IC-7300 last week and it had four LSI microprocessors with over 160 connections. These chips were about 2 inches square. No pots or IF cans that you would see in older radios. Everything is software in the alignment and tuning. Only the RF amplifier and low pass filter board looked like it could be worked on.

Nice article and thanks for sharing.
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by K3EY on January 28, 2017 Mail this to a friend!
K6AER welcome to the new world of throw away, like points in cars are long gone so is everything we used to fix with a screw driver. I like my IC7300 even knowing you're so right. I liked my TS520S & TS830S too but that was yesterday.
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by KB6QXM on January 28, 2017 Mail this to a friend!
I like "classic" radios, but I simply do not have the time to spend time troubleshooting them if anything goes wrong. My time is too valuable. I would rather give them to someone who has all of the test equipment. Call me when the radio is done. Ham radio is for people that have copious spare time. If you are retired, then take up the pursuit. Here in the Silicon Valley, spare time is a rare commodity.

73
 
Aging Issues With Past Century Kenwood Equipment Reply
by VE7VJ on January 29, 2017 Mail this to a friend!
Also check for back up batteries. I have a TS450 which has a button cell (CR2032) on the front board behind the controls. They can die or leak and damage the boards. I bought a button battery holder and soldered long leads so I could position it inside on top where it is easier to get to.

Larry N
VE7VJ (have to update my call-sign)

 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by K9MHZ on January 30, 2017 Mail this to a friend!
"I looked into the IC-7300 last week and it had four LSI microprocessors with over 160 connections. These chips were about 2 inches square. No pots or IF cans that you would see in older radios. Everything is software in the alignment and tuning. Only the RF amplifier and low pass filter board looked like it could be worked on."

Yeah, a day will soon arrive where one of the biggest things differentiating one rig's quality over another with be its algorithms. At least the traditionally failing devices like electrolytics will be at a minimum. Like you wrote, cans, pots, etc....adios.

 
Aging Issues With Past Century Kenwood Equipment Reply
by W0CBF on January 30, 2017 Mail this to a friend!
Great article. I really enjoyed reading it and agree with you. I work on a lot of Heathkit equipment and still enjoy that endeavor.

73's W0CBF
http://kcham.com
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by GM1FLQ on January 30, 2017 Mail this to a friend!
"Here in the Silicon Valley, spare time is a rare commodity."


Funny thing is though......when you wake up dead one day (one of life's certainties for us all) Silicon Valley will carry on just the same.
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by K9MHZ on January 31, 2017 Mail this to a friend!
I don't think that ^^^^ post was necessary, do you? Maybe his passion is his work and that's what he really enjoys.
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by GM1FLQ on February 3, 2017 Mail this to a friend!
About your ^^^^^ post - kind of typical from you and that's fine, but I prefer to take advice from those whose opinions are less ill-conceived.

I am sure the seeming liberal outlook you are keen to portray will allow you to understand/accommodate that different viewpoint.
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by K9MHZ on February 3, 2017 Mail this to a friend!
"Liberal"? Eh, you lost me, OM. That's OK.

BTW, your callsign doesn't come up on the eHam-QRZ link or the QRZ page directly. Just to let you know, because sometimes unlicensed wannabes show up here and post.

Best.

 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by GM1FLQ on February 4, 2017 Mail this to a friend!
It's ok, irony is often lost on those that like to display the so called "live and let live" mantra.

As for QRZ - seemingly run by PC huggy fluff liberals also of the live and let live ilk and whom banished me from their kingdom because they didn't like my views very much.
Yes the old live and let live, so long as you live aligned with their view, strikes again.

I instructed them to remove my details as have others - this is why many jump to wrong conclusions when a call doesn't appear on QRZ.
You see, contrary to what they would like everyone to believe (and many poor souls do), they are not the panacea of call look-ups - their database is not complete and most probably far from it.
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by GM1FLQ on February 4, 2017 Mail this to a friend!
http://www.eham.net/ehamforum/smf/index.php/topic,112932.0.html
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by N8FVJ on February 4, 2017 Mail this to a friend!
With crystal IF filters aging, it is nice to have Collins radios with the mechanical filters.
 
Aging Issues With Past Century Kenwood Equipment Reply
by K5UJ on February 5, 2017 Mail this to a friend!
<<<My time is too valuable. I would rather give them to someone who has all of the test equipment. Call me when the radio is done. Ham radio is for people that have copious spare time. If you are retired, then take up the pursuit.>>>

Let us know how we can compensate you for all the valuable time you wasted, posting a lament that added nothing to the topic at hand. I am very sorry to take up your valuable time with this message.
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by K9MHZ on February 5, 2017 Mail this to a friend!
Pedro, your bench looks great. What a setup!
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by GM1FLQ on February 6, 2017 Mail this to a friend!
"Let us know how we can compensate you for all the valuable time you wasted, posting a lament that added nothing to the topic at hand. I am very sorry to take up your valuable time with this message."

.....nicely put K5UJ.

Until I read the last sentence of his post I was starting to think that '6QXM was maybe the POTUS.
 
Aging Issues With Past Century Kenwood Equipment Reply
by KD7RDZI2 on February 7, 2017 Mail this to a friend!
I recently got a TS811 and was a bit worried about it but works quite well. Also the TS811s seem to be prone to the ageing issue at the IF cores which are used for both the receive and transmit. And if you don't get TX full output you will have likely an issue in RX sensitivity. I was told it is because of ageing, 30 years! But still, why 50years Drakes have not these issues?
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by ON7WP on February 8, 2017 Mail this to a friend!
thanks for the comments on my work bench. You should see my shack table, a lot worse... More weight, more levels, more depth...
 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by ON7WP on February 8, 2017 Mail this to a friend!
50 year old Drakes were built with components that were designed to last. 10-20 years later they started optimizing the production for more profit. Component quality went down. Same with cars. recent generation is all throw away. No sensible soul would repair a IC7300. I discovered a bug in my IC7000 that was from the first production runs. A wrong value of resistor in the mike amp caused overmodulation even at the lowest mic settings. I found the wrong part but could not fis it as it was too small....

 
RE: Aging Issues With Past Century Kenwood Equipment Reply
by KF4HR on February 10, 2017 Mail this to a friend!
As the inventory of specialized components such as certain IC's, digital and CRT Displays, etc, dry up the only option for repair on some of this older equipment will be by salvaging parts from another piece of broken equipment, and even this salvaging method will meet its eventually end. There are already radios from the 70's, 80's and even 90's that fall into the salvage repair only category.

I would imagine tube rigs from the 50's and 60's will still be repairable long after more modern vintage rigs become door stops.
 
Aging Issues With Past Century Kenwood Equipment Reply
by KC8MWG on February 11, 2017 Mail this to a friend!
Something else to be aware of is bad solder joints. I don't know about any other models, but apparently the nearly 40-year-old TS-120S is notorious for developing bad solder joints because the flux wasn't "cooked" out of the solder when the radio was assembled.
 
Aging Issues With Past Century Kenwood Equipment Reply
by KB2DHG on February 20, 2017 Mail this to a friend!
I have an old ICOM 745 that I think the trim capacitors are going bad, the radio will be operating fine then just drop out. I cannot do this repair myself but would like to know if there is a good reputable honest person out there that can do this repair for me?
 
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