Who says technical articles are boring !
Hello vintage kenwood all mode rig fanatics...
This is the mod you all have been waiting for !!!
Are you one of the proud owners of a TR-9500, 9000 or TR9130 ? Is your display erratic and flickering as 95 % of these still existing radios on the planet. Then this is the cure you have been waiting for during the last 25 years.
This mod was created because this phenomenon was getting on my nerves and I was so sad nobody did something about it, we even kept buying their rigs, the TS-930 with the rotten finals, the TS440 with the VCO gum problem, the TM255-455 with the distorted SSB TX audio, the TR2600 with the noisy synthesiser... (yes we all know that kenwood sucks but the're still on the market...) I do like the 2000 however, but the user interface is designed for aliens. So far the commercial break.
Back to basics. Essentially there are three different problems with this rig's processor board. Most units I saw suffered from more than one problem. Here we go...
Please start by downloading the service manual from this site. I will use the original kenwood reference numbers. Don't send me silly mails to ask for foto's showing the component locations. If you are a decent ham, you do know how to read a schematic and trace components on a board. If you're not, stop reading and start watching Oprah on the telly.
The gossip is that the print batch suffered from bad via's, this is what the plated through holes are called. THIS IS NOT THE TRUTH !! The whole problem is purely thermal. Bad design. That's what Kenwood stands for.. (not that the other brands are any better, they just want to get richer using cheaper components all the time)
There are mainly three possible problems:
1. disappearing display segments. Mostly the rigs powers up ok and after some time the christmas tree starts blinking. The causes are bad solder joints at the 7 series resistors (R15-21) of the display leds. If you are good at soldering and have the tools, desolder them, clean the board and resolder them, preferably using silver solder, having a higher meltdown point. Only resoldering will also help but only temporary. It might be a good idea replacing them by 1/2 W resitors, having a bigger body, so better thermal behaviour. Even better is replacing them all by 150R units. This lowers the visibility but decreases the heat. Haven't tried this myself but I suggest it would be even better. Better a faint display than no display at all...
2. disappearing complete digits. Same thermal problem at the 5 driver transistors Q22-26. Resolder using preferably silver solder.
3. resetting processor. Unit jumps to 3.000 or 5.000 during operation. This is caused by unsufficient voltage at the processor. You won't believe this: On the board is a test point TP1 next to Q10. This big test pin is soldered on both sides of the board, but this solid pin behaving as a bad resistor is the reason why the processor doesn't get sufficienty juice. Resolder it on both ends (again using silver solder...this is getting boring) and check the voltage on pin 21 of the processor and pin 16 of both other IC's, this voltage must be over 4.5 Volts. If not ok, also check the soldering of D5.
This should cure most of the problems. There are some other faults I found on some units. I just mention them to get you back up and running if the above tips weren't sufficient:
* defective Q3: 1.5 Volts Vbe and no Ic. Replace by any NPN transistor but observe pinout.
* defective Q9: replace by any 7805 and try to improve cooling, or increase value of R15-21 to 150R.
* defective (open) D1 zener: if you have bad luck your processor is toasted by the 8V but I saw some survive this.
This is it from your favourite Radio-Doctor and Transceiver-Guru.
If this mod was useful for you, please drop me a small mail with your repair adventures. This keeps me motivated to post these funny mod files. If you are really wealthy, your donations are accepted to keep my multiple repeater sites on the air, so I can use my hobby money for my own fun...
Pedro M.J. Wyns
Postpigeon: Moutstraat 7
E-Mail: ON7WP @ pandora.be
The service docs can be found on this great site, thanks Erik !http://www.mods.dk
DISCLAIMER: This article may be printed, copied, published, archived on any medium, recorded, , encoded, broadcasted, uplinked and may even be bodypainted on the corps of the Queen or the butt of Mr. Bush, as long as it is kept original and unmodified including all headers and footers, and as long as credit is given to me, the author.
PS: I hope the Kenwood guys (and the Queen and Mr. Bush) are in for a joke, or I won't get any access to spare parts anymore....