EB5AGV's Kenwood TS-930S page

Kenwood TS-930SAT Kenwood TS-930SAT

Welcome to the Kenwood TS-930SAT 'On-line restoration' page. Initially I planned to update this page as my restoration advanced. But I have been lucky enough to repair the rig in short time so you will get the full picture already. Anyway, if you want to contribute anything, please, feel free to send me a message. Thanks!

TS-930SAT Repair Notes


All of this started when I saw a message in the uk.radio.amateur newsgroup about somebody selling a TS-930SAT for 'repair/parts'. I am always looking for gear to fix, so I found this could be my next 'winter project'. I offered a reasonable amount for it and the deal was made. Preliminary information about the set revealed it had some trouble with the power supply section. As I fastly found, the power supply is not one of the best thing Kenwood did in the 930. It is, in fact, a poor design, lacking protection and convenient heat dissipation. More on this later.

Rig was offered along a hand microphone (MC-43S), User's Manual and a very interesting spare digital board. This last is really nice to have as another flacky point of this set is the through hole vias in the digital board which, when fail, produce a full array of troubles. Owner bought the spare board thinking the fault was there but he swapped it and found it did not help. The rig came also with an optional AM filter (Kenwood 6kHz) but no extra CW filters.

It was a 504xxxxxx serial number (so made in April 1984). At least it was not a first series model, which seems had more troubles.


After some days, the rig finally arrived to Valencia. I went to pick it up and found a very nice packaging job (thanks, Tony!) and everything as promised in a large box, which contained another one where the rig was. It included also an interesting 'Technical Information' booklet (about 40 pages long), depicting the most important features and circuits of the one time 'top of the line' Kenwood. It is a technical report, very interesting to read. I have put it online here: TS-930S Technical Information

Here you have the cover of this document:

So I rushed to my shack and put the rig on the workbench. I had been told that it was not working and only the dial light worked... so I connected it and, yes, anything else worked. Front panel multimeter indicated about 15% deflection. Of course, no display nor any signal on the speaker. So I had a winter project!

I got to the power supply unit, not an easy task, as you need to move the power supply transformer, fan cage and some brackets and all is connected with heavy gauge wire along some tiny connectors. In this picture you can see the power supply unit and its location in the rig:

As you can see, power supply unit is in a crowded zone:

But well, I could reach the PS unit and found some hint of what could happen to the rig: there were signs of bad soldering joints in the rectifier diodes, which had lead to some burning in the printed circuit board. I also found a dead transistor in the same board and I guessed it died because of the intermitent contact in the diodes. This last transistor controls a 22VDC supply to a zeners / resistors array which in turn generate unregulated 16 and 8 VDC to the digital unit. As the transistor was faulty, the digital unit would not work so the rig was dead. Dial lamps lighted and 28VDC main voltage was present, so the power transformer seemed to be in good shape.

So I replaced the offending transistor (2SC2235) with an european BC639, as characteristics were close enough. Everything else checked right in the PS Unit and also in the associated circuits. So I applied power and got the rig working!!!. Display lighted, all keypad functions and knobs worked, the rig received signals... I was really surprised for the easy repair. I had partially dismantled the rig to get to the power supply circuit so I put it back to place. I found some screws which were loose, so I tightened them. Then I powered the rig again.. and nothing!. Display was dark. Only the S-meter lamps glown. I thought about the digital board not reseting. So I unpowered the rig and powered it back. And then I got the common noise you get when something burns. Dismantling again the power supply circuit I found the recently changed transistor was dead. And also the 24V zener diode it had associated. Although it passed the diode test, it seems power transistor (2SD843) was gone. And, as I discovered later, also zeners in the fan cage were gone. Well, not bad at all... dial lights still lighted ;-)

So I needed to rework the power supply. And had some questions:

Of course, there was a chance I had damaged something else with the 22VDC going 28VDC. I was afraid I did. So I left everything prepared for next day and went bed thinking about what I had done wrong...


To fully understand this message I am afraid you will need the TS-930S Power Supply Unit schematics (for rigs with S/N bigger than 309xxxx). So I have put it here in case you need it:

Download Power Supply Unit Schematic

I replaced the 2SC2235 (Q6) transistor with a BC639 (a bit lower voltage rating but similar parameters otherwise), the 2SD843 (Q3) with a BU807 (it is a darlington in TO220 capsule, 8A nominal Ic max, diode protected output). I also replaced surrounding 2SC2235 components (24V zener, 22uF capacitor). Zener diodes in the fan cage were also replaced with 8V2/1.3W zeners (I had not 7V8 zeners available). A preliminary unpowered check was good so I powered the rig with the digital board power connector disabled. Voltages came fine enough: about 22V from the BU807 collector and good zener regulated voltages. So I powered down the transceiver, plugged the digital board power connector and checked again. Again, all was fine. Display did not light, as I expected (too much luck is not good for winter projects ;-) )

Disconnecting connector J9 in the digital board, which carries the UL (UnLock) signal from the PLL board to the digital board produced the result I was looking for: dial lighted, showed info and tuning and rit knobs worked. Band change buttons were also operative. No audio from speaker, as PLL was not working. Some functions, as attenuator, did not work (relays were not heard).

Up to this point, it seemed 7818 regulator in Signal Unit had opened. Reason for this should be the momentary 28V in the 22V line, when the 2SD843 shorted. Good thing is that GOOD 78xx regulators use to die that way; they get open. Beware with this, as there are not so good 78xx regulators in the market. In the company I work for we got a batch of them some time ago...

So I powered down the rig and had a dinner :-). Then I came back, put the DVM in the BU807 output, powered the set... and got only 4V!. Checking again PS board I found BC639 was dead. It seems the poor designed 24V mini-supply failed on startup. I then thought about adding a collector resistor (about 20-50 Ohm) to limit the power surge on startup.

So the rig was not working yet, but I got interesting results, which I summarize below:


As the PS Unit was faulty again, I replaced all faulty or suspicious components in the 22V supply: rectifier diodes (I put a pair of 1N5408 replacing the U05Bs), control transistor (2SC2235; I replaced it with a BC639), power transistor (2SD843 replaced by a BU807) and zener diodes (7V8 replaced with 8V2)

Preliminary checkings showed it was working fine. But still no signals heard and I should disconnect J9 in digital board (so disconnecting PLL Unlock) to get the display lighted, as before last PS fault. Something was wrong at the Signal Unit.

So I put back power transformer and PS circuit in order to be able to put the rig on its side and to look at the bottom side, where the Signal Unit is located. I checked the input to the 7818 18V regulator to find 22.5V at about 900mA. So the regulator was not opened, as I first thought... Time to get out signal unit!. About a zillion screws later ;-) I got it hanging on some wires... and then I located the culprit of all my troubles!. It seems previous owner, trying to get the rig working, dismantled lot of covers and assemblies. I know this because there were lots of screws which were not tight. Well, he had put a long screw (the ones used to fix the digital board) instead of a shorter one to fix a cover in the upper side... so the screw was shortcircuiting one pin in the signal unit (pin 14 of IC11; just the power input to the chip!). I thought this short could have ruined some parts. But once the offending screw was removed, I put back all pieces and powered the rig, to find it was working fine in all of its functions, transmission and automatic tuner included. Hooray :-)!

Summing up, now the rig worked fine and was able to do my first contact with it.

So I took all the knobs and carefully cleaned them. Here you have the rig without any knob... curious, isn't it?

Once the knobs were again in place, I checked sensitivity in several bands using my trusty HP-8640B generator. I got lower than usual readings in all bands... So I suspected about a common switch element (sometimes I get good ideas)... and found that cleaning the rear panel 'RX ANT SWITCH' completely cured the problem. It was as sensitive as my fully aligned Collins KWM-2A.


I have only added one component, a 47 Ohm resistor in the 2SC2235 (a BC639 in my case) collector (opening the trace from J7 pin 1 to R23 and inserting it there), to protect the transistor from power surges and dangerous V*I products. And have done also a simple change in the PS circuit, puting the PS fan always on, connected to the unregulated 8V supply. This way it runs slower than with nominal 12V, but it prevents components temperature cycling as it happens with original thermistor controlled circuit. I have thought about adding a 7812 in the fan cage and allowing selection of 'standard' and 'low' fan speed by means of a switch. Next time I need to open the rig, I will probably install this mod.

Here you have a picture of the rig working, still without covers.

By now, this is the end of the story... I will add more information if I work more on the rig. Thanks for reading!

Go back to Main Page