Adventures in Radio Repair - Kenwood TS-480SAT Will Not Turn On

Discussion in 'General Technical Questions and Answers' started by KG4MSR, Apr 20, 2017.

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  1. KG4MSR

    KG4MSR Ham Member QRZ Page

    Greetings folks. I thought I would share with you a short story and a repair tip for the Kenwood TS-480SAT.

    The radio originally belonged to one of my Elmers (I’m lucky, I have many to whom I am grateful for) and developed trouble - the radio would not power on. KC0JGF, now SK, attempted to fix the radio, and even posted back in May of 2012 in this forum to ask for troubleshooting help. The radio was then sent to Kenwood but was returned unrepaired. My Elmer received the radio back from KC0JGF and thought I might like to try my hand at it. Since KC0JGF’s original forum topic ended with no resolution, I thought I’d start this post to provide some closure.

    Problem: Radio would not turn on. When pushing the power button there were no lights, nothing on the LCD, no fans, and no apparent signs that the radio was doing anything except a slight current draw (under 100 milliamps if memory serves me right) noticeable for several seconds and then no current draw.

    Troubleshooting: The voltage coming into the radio and through various regulators tested good. The control cable tested good. The firmware flash switch was in the proper position for radio operation. All screws and connectors were tightened and reseated. The microprocessors in the RF deck and control head appeared to be operating as per service manual voltage tables with no reset functions (no over voltage conditions, faults, etc.) being enabled. A month or more passed with the radio on my bench, as I would poke around for an hour or so one night and then the next. My Elmer, the original owner of the radio, told me I could keep the radio - even if I fixed it. I think he thought repairing the radio was futile. I thought the same but figured I must go on with the troubleshooting - I just had to figure out what was wrong with the radio. Maybe the radio just needed a good ole’ firmware reflash? My computer would not recognize the radio for computer control or firmware upgrade. The programming cable was a known good cable.

    Solution: My computer would not recognize the radio… this was the “ah ha” moment after many head scratching hours at the workbench. This prompted me to work from the RS-232 port back to the microprocessors in the RF deck. The VCC for IC203, a level converter, was correct but the outputs CS1 (pin 12) and RD1 (pin 9) were under a volt (supposed to be more than that). These lines were traced to IC207, a buffer. The VCC to IC207 was under 2 volts (supposed to be 3.29 volts). VCC was correct on the other side of R341 (so VCC to IC207 was good, as well as R341). C234 tested good (no short to ground or significant resistance to pull the voltage down). I reasoned that something had caused either of the two ICs to go bad… and which one went first, I don’t know, but knew they were both bad. Perhaps a bad programming cable caused the problems? I’m still scratching my head on this.

    I’ll admit that my surface mount skills are just… ehh. I hate disclaimers but should say that I don’t recommend you try any of the following at home unless you are intimately familiar with SM components and have the proper tools for removing/installing SM components. I do not have the proper tools, nor am I intimately familiar (although I did successfully complete a Softrock transceiver kit), so needless to say, removing the ICs (they are those real small surface mount ICs, about the size of a dear tick) was a real challenge and took a little luck. After removing all the solder from the pins the darn things still wouldn't come off the board until I carefully cut them in half with miniature wire cutters (yes, I know, doom on me, I’m evil). Thankfully I did not destroy any of the solder pads on the circuit board.

    Replacement parts were ordered (under $30, including shipping) and then installed. Installation required a good magnifying glass and a steady hand but the hard work paid off… The radio was fixed! I was so excited once I saw the LEDs light and the LCD say ‘Hello’ I could have done cheetah flips! Receive and on-air tests on both SSB and CW proved the radio was again a very nice functioning transceiver. Once I realized what a nice radio I now had in my possession, I offered the radio back to my Elmer. To my surprise he told me to keep it. I couldn’t abide taking such a nice radio but we agreed that I would owe the rest of my Elmers future repair work. Deal.

    So that is my adventure I thought I’d share with you this evening. I hope you have enjoyed it and may it aid in your own radio repairs. 72
    KC8VWM and K5URU like this.
  2. KA0GKT

    KA0GKT Ham Member QRZ Page

    Good Job!
  3. KL5A

    KL5A Ham Member QRZ Page

    Chip Quik is your friend for removing SMD's. It's a strange solder like substance that mixes with solder and reduces the melting temperature so the solder stays open longer. A quick wipe and the chip comes right off.
  4. KG4MSR

    KG4MSR Ham Member QRZ Page

    Thanks for the tip, KL5A. That stuff will be on my next parts order. Much appreciated. 72
  5. KL5A

    KL5A Ham Member QRZ Page

    I still can't hardly fix them but at least I can get the bad chips off!
  6. KV6O

    KV6O Ham Member QRZ Page

    Great! It's an excellent feeling of satisfaction when you see something power up from the dead. Congrats!

    I have a hot air SMD tool that takes some practice, but works great.

  7. W9GB

    W9GB Ham Member QRZ Page

    ESD Events or Operator Error (Cable wiring errors) via RS-232 (or USB) port is common.
    Reverse DC Polarity seems to be common problem with "Non-Tech" amateurs.
    Easy to prevent with standardization of Radio Shack wiring.
    The First Lesson in Troubleshooting is that the External World is not safe for Electronics.
    While component failures can occur .... the I/O (power, interface) to the Appliance/Box/Radio is the door that "terror" enters.
    ** In your instance, the problem entered through the Radio's RS-232 serial port. Fortunately, the RS-232 level converter and buffer "took the hit" and not the radio's multi-pin microprocessor **
  8. KG4MSR

    KG4MSR Ham Member QRZ Page

    Thank you Steve,

    I reckon a hot air station should be on my future purchase list... I came close to buying one when I was given an old laptop to play with that had the dreaded 'no video' problem due to the graphics processor unsoldering itself from the motherboard. I opted for baking the motherboard in our countertop toaster oven (wife wanted a new one anyhow and I really wanted to try it!). Now I have a working old laptop! 72
  9. KG4MSR

    KG4MSR Ham Member QRZ Page

    W9GB - That's what I figured might have happened - bad cable of some sorts. Your insight assures my troubleshooting logic was on the right track. And yes, the world can be a very cruel place for electronics. 72

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