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Author Topic: TS-930/TS-940 Power Supply "Crowbar" addition to protect final unit?  (Read 4611 times)
N6QWP
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Posts: 263




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« Reply #15 on: November 19, 2017, 05:10:10 PM »

So.....as to a "serious power supply upgrade", is the ONLY tried and tested one available the "A5LX Mod" Huh  Can you reference other published upgrades that you consider "fail safe" Huh  What would you recommend as the "minimum upgrade".....that would negate the need for a crowbar Huh

Please remember, we are looking for some sense of security....as to the prevalent and impending catastrophic failures that destroy expensive and hard to get (and difficult to replace and realign) parts.  

I would love to "move on"......if I were to feel that the requested mods were not necessary.  Several other owner-contributors seem to feel otherwise.  What upgrades did you do to feel comfortable?

It is easy to dismiss the concerns of others--if it is all theoretical.....not so much so, if it relates to your primary rigs and the investment of time and money required to rebuild them in the event of a failure (that might be prevented-with the proper mods).  
 
« Last Edit: November 19, 2017, 05:30:28 PM by N6QWP » Logged
KM1H
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« Reply #16 on: November 20, 2017, 02:56:16 PM »

I did all my work long before there was an active ham hobby Internet and havent had a need to look at what has transpired since then since nothing failed.
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N6QWP
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« Reply #17 on: November 20, 2017, 05:03:23 PM »

Thanx, but that does NOT help any of us who are presently seeking solutions to the documented weaknesses of the TS-930 OR TS-940.

This thread is ONLY seeking PUBLISHED (online) MODS to overcome the known deficiencies that might very well subject our radios to failures that we would rather avoid.  Life experiences that can NOT pass along actual PRACTICAL mods--THAT WE CAN FOLLOW AND IMPLEMENT, do NOT help us to protect these old radios in the present.

I am sure that there are many, many hams that have not experienced failures in these radios.  That is not what we are wanting to know.  We are glad that you all have not had any catastrophic events.  We are posting this thread (once again) for the benefit of those who have acquired and are PRESENTLY using these venerable rigs.....and are looking FOR MODS to preserve them.....as best we can.
« Last Edit: November 20, 2017, 05:25:03 PM by N6QWP » Logged
N6QWP
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Posts: 263




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« Reply #18 on: November 20, 2017, 05:49:59 PM »

For clarification....I am talking about TS-930 and TS-940 radios that are presently working and have-as yet-NOT BEEN MODIFIED.  

The task at hand is to gain the MOST UPDATED AND PROVEN modifications that can help to prevent the well known problems associated with the failure of the power supplies.....and the resulting damage to the final unit and the AVR board.....and of course, whatever else could be "downstream" and susceptible to the resulting over-voltages.  

These rigs are getting older and are more likely to experience failures than in the past due to the aging parts.  By publishing these posts, I am attempting to elicit practical knowledge from the experienced old timers and the more technically proficient that can be utilized by those of us who are less so.....but still dedicated to.....and invested in upgrading and keeping these old radios alive.
« Last Edit: November 20, 2017, 06:08:22 PM by N6QWP » Logged
VE7DQ
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« Reply #19 on: November 20, 2017, 09:41:13 PM »

Flickering S-meter lamps while in receive mode are an indication that the pass transistors are failing and about to short!  

That's important enough to emphasize as I've been fortunate enough to catch the failure in a few cases before it went catastrophic, unlike the one and only that burst into smoke and flames on the bench in front of the owner!

It's my opinion that pass transistor failure causes all the downstream damage, not the other way around.

There were two series of TS-930s that I am aware of, before S/N 310XXXX and after.  At 310XXXX there were changes to the signal board and the power supply layout, among others.  My preference is the later radio, although I have one of each, early and late.  I've read on the internet that there may have been a third revision and schematic, but I've not seen it and remain skeptical of its existence.  In any case, the '930's serial numbers don't seem to matter when it comes to PS failure.

I would replace R4 and R5 on the AVR board with flameproof resistors without hesitation.  Pass transistors should be replaced with 2N5886s, from a reputable source; they have better specs than the '5885s.  Most '930s came with a silicone sheet between the pass transistors and the heat sink.  In replacing the pass transistors I would normally exchange those silicone sheets for mica insulators with a thin smear of thermal compound on each side just because I'm old-school.

There is no realignment involved, other than resetting the idle current to the new drivers... and the finals, only since one is already there.

Some very early '930s (S/N 208XXXX and somewhat up) had the final unit fan blowing hot air into the chassis.  There was a service bulletin and kit to improve the airflow characteristics.  One modification I did on several '930s was to add a small-value resistor across Q6, emitter-to-collector, under the AVR board so the power supply fan would run at reduced speed continuously.  This had the effect of cooling the whole radio.  I don't recall the value, but it can be determined experimentally.  The cooling fans, however, aren't very robust and trend toward becoming mechanically noisy as they age.  There used to be a springy thingy available from Kenwood that would bear against the fan's shaft to help quiet the rattle.  Don't bother looking for one; they're long gone.

Most of Kenwood's service bulletins for the '930 are still available on line and there is one listed for transient suppression.  I've never done this mod, but it may have some merit.

I don't recall ever having to do power supply fixes twice on the same radio.  Most '930s (and '940s) chug along for years without any kind of repair; reference KM1H.  

Having typed that... here are a few links for reference:  

http://www.onsemi.com/pub/Collateral/MC3423-D.PDF

https://forums.qrz.com/index.php?threads/mc3423-alternate.254483/

http://www.wa4nve.com/page5.html

http://w3afc.com/uploads/3/5/9/3/35934954/a_compendium_of_information_on_repairing_your_own_kenwood_ts-930s_rev_7a.pdf

VK4AMZ had a modified AVR board that used an MC723 voltage regulator, I believe, but his site does not appear to be on the web any more.  The board may be still available from 'FAR Circuits', so it might be worth a look there.  I have no experience at this time with this mod.

Regarding crowbar overvoltage protection in general, there's an article in the May 2017 issue of QST on page 32-33 that may be of value, particularly figure 1, which shows a simple generic circuit albeit without component values.  Unfortunately, the article is not available for download or viewing even by ARRL members (?!) so you must find a hard copy if you choose to explore this direction.

OVP is not in Kenwood's lexicon, and remember: the fast-acting protection fuse is often protected by the faster-acting transistor.    Shocked

Six hours: I'm done.
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KM1H
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« Reply #20 on: November 21, 2017, 07:27:35 AM »

Quote
This thread is ONLY seeking PUBLISHED (online) MODS to overcome the known deficiencies that might very well subject our radios to failures that we would rather avoid.  Life experiences that can NOT pass along actual PRACTICAL mods--THAT WE CAN FOLLOW AND IMPLEMENT, do NOT help us to protect these old radios in the present.

What is already documented is all you need for long term reliability. Continuous harping on OVP is wasting time, update the radio and use it.
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N6QWP
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« Reply #21 on: November 21, 2017, 07:58:52 AM »

Thanx for all that valuable information.  Seems like, except for a crowbar addition, the mod by A5LX appears to be the one of choice-at this point.  Combining that with the info from VE7DQ and confirmation by KM1H, we probably have enough to proceed.  

***Too bad that we can not access the mod by VK4AMZ.  If anyone has a copy of that, we'd love to get the info!***

Still waiting for updates from ZS5WC on his mods.....but will start with what we have at the moment.  Thanx again, one and all.  Sometimes, it is like pulling teeth, to get enough of a consensus of ideas to feel confident enough to go forward when attempting the unknown.

We couldn't do it without the unselfish contributions and time of those willing to Elmer us in these searches.  I hope that we have gathered enough practical information to help any other owner-users of these fine old TS-930/TS-940 radios.......to keep them from imploding, so that they can provide many more years of service.  Thanx and 73



« Last Edit: November 21, 2017, 08:12:17 AM by N6QWP » Logged
N6QWP
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Posts: 263




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« Reply #22 on: November 21, 2017, 08:35:07 AM »

*****UPDATE!!!*****

The mod by VK4AMZ IS AVAILABLE ONLINE!!!  IT IS FOR A REPLACEMENT AVR BOARD FOR THE TS-930.

 While never completed (due to health issues), the breadboarded prototype and circuit are to be found online.

FARCIRCUITS SUPPOSEDLY HAS THE CIRCUIT BOARD FOR $7-JUST ORDERED ONE?Huh  

Waiting to see if this is still available?

*****Would love to hear from anyone who has tried this modification on their TS-930.*****
« Last Edit: November 21, 2017, 08:53:18 AM by N6QWP » Logged
N6QWP
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Posts: 263




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« Reply #23 on: November 22, 2017, 03:02:20 PM »

VE7DQ has kindly provided the best links and info above for several modifications to the TS-930-that appear to be the answers to any problems with the original power supply.  Both seem viable....just wanted to point that out in case anyone else inadvertently skipped over those links.

As of now, until other mods....that are hopefully coming after the Holidays, the mod by A5LX appears (to me) to be the only illustrated, step by step update that I can find for the TS-940's power supply's problems.

The circuit board from Far Circuits is available for the 930 mod by VK4AMZ for $7 plus $3.50 S&H.  Until I research the availability of the required parts for this mod.....I am undecided between it and replacing the original with the switching power supply.

I still have a question about which of these might work best for the pre or post 3 million serial numbered 930's (without changes) Huh

Anyone else who tries-or has tried-either of these mods for the TS-930 or for the TS-940, please come back and let us all know how it works (or worked) out.
« Last Edit: November 22, 2017, 03:17:21 PM by N6QWP » Logged
KB1MIQ
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« Reply #24 on: November 24, 2017, 06:57:19 AM »

Ah !  You're talking to me !  I hope this comment proves helpful.
 When it comes to radios, I'm dumb as a box of rubber nails.  Electrically that is.  The original TS-9330/940 power supply is junk after all this time.  Mine was putting out 36V. at the taps. My TX power was about 3 watts.  W3AFC  has step by step instructions, for power supply replacement.  So I replaced mine.  I assume this vimeo hasn't escaped notice by the 940 guys:

https://vimeo.com/239531940

I elected to modify my AVR board, but there's plenty of information about the dc/dc step down boards from china that can be had for just a dollar or three. ( if you want the fancy one that has the LED readout of the voltages going through it. )  They are on ebay.

www.W3AFC.com

My finals are good in my 930, while my AVR board was bad, the rest of the radio seems OK.  I don't know yet.  I don't have a dummy load, have no antenna, yet.  I will come back in a week or two and up date all this.  Tools for the job ?  Ohm meter, solder gun.  I had to buy a solder gun.  So you can imagine my level of skill.
  There are really good folks out there, that really know what they are talking about.  I guess not all of them would agree with the fix John has documented.  His fix is focused on the 930 but the 930 and 940 have a lot in common with the power supply. He does address both pre and post 31XXXXX serial number radios.
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N6QWP
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« Reply #25 on: November 24, 2017, 11:06:46 AM »

BINGO!!!!

Great information.  The videos and pictures that we now have available are indispensable.

Anxious to hear back from you as to your final results.  Thanx!

Anyone who is following these threads now has a pretty complete set of options for redesigning and fixing the inherent weaknesses of the power supplies and AVR boards in both the TS-930 and the TS-940.

The task at hand, is to decide which mods to follow.  The decision will depend on parts availability, price and difficulty of completing the mods.
« Last Edit: November 24, 2017, 11:23:22 AM by N6QWP » Logged
WA1RNE
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« Reply #26 on: November 28, 2017, 09:48:11 AM »

 Besides what I've already posted concerning the crowbar circuit design, I've finally had access to some decent photos and videos from AL5X and Jeff Hillard's Vimeo page and came away with a probably cause for less than stellar reliability of the 28.5 volt PA supply:

 The heat sink appears to be woefully under-designed, even with that paltry fan mounted in the middle. I don't have the exact dimensions of the heat sink but scaled to the IEC Ac line connector, I'd say it's approx. 3" x 5 3/8" overall with (16) 3/4 x 3 inch fins.

 The PA input requirements are ~250 watts and at high line, the pass transistors are seeing ~13.3 volts and 9 amperes fully loaded or 119.7 watts, plus 7-10 watts for the bridge rectifier and another 5-7 watts for the 3 terminal regulators, or approximately 134 watts.

The available surface area of this heat sink is approx 64 sq".

 The general rule of thumb for a heat sink is 1 sq" per watt of dissipation, so as you can see, I have no idea what the fan's CFM rating is but it even with the little fan this heat sink is very undersized.

 I would concentrate on the following modifications:

  - Increasing the heat sink surface area using a similar overall size but with longer fins and a better fan;

  - Adding emitter ballast resistors (0.1 ohm, 5 watt each) in series with each pass transistor to increase sharing and decrease the chance of thermal runaway;
 
  - Get the crowbar circuit straightened out - add a gate to cathode resistor and a ceramic bypass capacitor in parallel with it to guard against false tripping.

 ...WA1RNE

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WA1RNE
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« Reply #27 on: November 29, 2017, 10:10:17 AM »


 I'd like to add a few more suggestions. My last post was cut short because of some internet connectivity issues:

 
Quote
The heat sink appears to be woefully under-designed, even with that paltry fan mounted in the middle. I don't have the exact dimensions of the heat sink but scaled to the IEC Ac line connector, I'd say it's approx. 3" x 5 3/8" overall with (16) 3/4 x 3 inch fins.

 The dimensions are approximate and someone should verify them.

 To verify my analysis, it would be very helpful if someone with a working 930 or 940 could take some transistor case and heat sink temperature measurements at the 2N5885/5886 using a good quality IR thermometer.  I use a DeWalt DCT414B which has settings for emissivity for various materials. I would try your thermometer on some samples of smooth aluminum and painted aluminum to make sure you are obtaining accurate measurements.

 - Case temperature should be made on the device flange, but away from the mounting screws and not on the metal cover.

 - Heat sink temperature should be made on the transistor mounting flange between the 2 devices.


 The test conditions for the measurements should be as follows:  all tests at 60-70 degrees F ambient

 1) Baseline ambient measurement:  Radio off for at least 2 hours, measure case and heat sink temps.

 2) Transmitter keyed, 20 meter band, CW mode, full power into a 50 ohm load, measurement after 30 seconds.

 3) Transmitter keyed, 20 meter band, CW mode, full power into a 50 ohm load, measurement after 300 seconds

 
Depending on the results, longer key-down times might be needed an some other potential improvements that might be worth considering are better thermal insulators, larger heat sink fins, better airflow, etc.

 ...WA1RNE
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KM1H
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« Reply #28 on: November 29, 2017, 04:46:13 PM »

Since I ran a pair of TS-930's and then 940's for over a decade of heavy CW and SSB contesting, which meant 44-48 hours in a 48 hour contest with nary a problem after repairing/upgrading the AVR board I see no reason to go overboard.
I did lube the fans yearly and increased the speed of the fan on that more than adequate heat sink.That fan mod came out in the 80's.

After over 30 years operating the 940's Id say Kenwood got it almost right in the PS and finals area.

Carl
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N6QWP
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« Reply #29 on: November 30, 2017, 07:57:59 AM »

Thanx RNE!

Thanx Carl--Care to share with us all, exactly what you did to upgrade and repair the 940 and 930 AVR boards (in detail, please)?  

Since there were/are, obviously, so many problems......(and "mods"!).....that have been/are still being experienced (especially since these radios are getting so much older), we'd love to get the "exact" actual work that you did=that you found so reliable.

Are you still using these radios and taxing them to the same degree....or was this in the past-when they were not quite so old and subject to the ravages of time?

"Inquiring minds would like to know"
« Last Edit: November 30, 2017, 08:18:49 AM by N6QWP » Logged
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