TK790H not powering up

[LostInHertz]

I’m installing a used TK790H in my vehicle for ham radio use, and I’m having problems with getting it to power up fully. I know just enough about radios to be dangerous, which means I know more than an average person about radios but I’m definitely not a professional radio tech.

The setup:
-An eBay purchased TK790H with single remote control head. The radio included a mic, KCH11 control head, control head cable, wires, brackets, mount, and external speaker. The included wires did not have an ignition sense power wire, but had everything else.

-Based on everything being included, my assumption was that it was a singular radio unit at some point in the past. I’ve since sent a message to the seller to see if that’s correct or not.

-The install included using two positive leads with 15 amp fuses on each direction to the battery, plus two negative leads tied into chassis ground. I don’t believe inadequate power is my issue (especially because I can’t even transmit yet).


The problem and my troubleshooting so far:
-It seems like the radio main unit is partially powering on but the display isn’t. Nothing happens with the display when the power button is pressed, nor does the speaker make the Kenwood beep when powering up, nor does any buttons do anything obvious. However, the speaker makes a faint pop when the radio power button is pressed to power down. The radio is drawing current as well judging by the little spark when I installed the initial fuse, but I haven’t measured how much current it’s using.

-I attempted to read the radio programming to see if it could be a programming issue (like being programmed for a basic control unit instead of the KCH11). The software will download 129 out of 180-something units, then it gives an error and won’t continue. That confirmed my suspicion that the radio has to be somewhat active even though the display isn’t working. If it matters, the software I’m using is KPG-44D, version 2.10. The cable is a Kenwood KPG-43U. I’ve confirmed the cable is running on the correct com port.

-Online research indicates that a common problem for similar problems to mine is the F502 fuse being blown. I checked that fuse with a multimeter and it has continuity. While in there, I checked the other fuse (F501?), confirmed the resisters are setup for a single control head, and confirmed the ignition sense resisters had not been changed from stock (meaning the resisters are still bridging R504 and R742). If my research is right, I shouldn’t need an ignition power wire (although I’ll return to this later in this post).

-The display keypad has an emergency button but there is not a scrambler chip or ANI chip inside the radio. I thought this was an interesting find because I thought the emergency button needed an ANI chip. I confirmed the resister jumpers are not in place for those chips either per the service manual info (edit: after re-reading this post and if my memory is right, there are resister jumpers in my radio and those chips require the removal of the resisters; either way I found that it was not set up for the scrambler or ANI chips when I was following along with the manual). This makes me wonder if a hack attempted to use this radio adyers its professional life was over and swapped button inserts or was inside of it.


I’m planning on trying a switched ignition source power wire tomorrow just in case that’s my issue. I am a little confused though on which terminal it goes into. I keep reading terminal 1 of the 9 pin connector, but I’m not sure if that’s right or left as I’m looking at the back of the radio. Can someone clarify that for me?

If that’s not my issue, does anyone have any suggestions for what else to try? Is it possible the F502 fuse is bad even though it has continuity? Is there a way to test the control head in case that’s my problem?

My final question is how can I tell for sure if this is a CalFire model or not? The seller was from the east coast, so my assumption was that it’s likely not a CalFire model. If it turns out to be a CalFire model, is there anything special that it requires?

I’ll sincerely appreciate any help that you can provide.

 

[tlemke940]

first thing i would do is check your control cables if those are tight i would remove the remote kit from question and connect the head directly to the deck like it would be if it was a dash mount. if that still don't work it may be bad firmware or a component failure.


for it to be a cal fire radio it needs one of 2 firmware versions i will need to look them up to tell. also you need fire service software. also added note fire service software works on a regular 790h if all you want is the 256ch capability

 

[LostInHertz]

Appreciate the suggestion. I’ll give that a try later today.

 

[LostInHertz]

Things I’ve tried today (but not necessarily in order):

-Applied 12v power to ignition sense feeds on the control head and radio.

-Installed the control head directly on the radio, bypassing the control head cable.

-Confirmed there is 12v on both sides of the F502 fuse.

-Confirmed there is 12v being sent to the control head.

-Confirmed the control head and radio body has ground.

-Checked the various reverse polarity protection diodes on the control board inside the radio.


I still can’t get the radio to fully power up. When it’s off, the is minimal power being sent to the control head (1 to 2 volts). When the power button is pressed, all 12 volts are sent to the control head and elsewhere. Again, that indicates to me that the radio is partially powered on, but the display does nothing.

I know this is wishful thinking, but is there a bench test that I can do on the control head to see if that’s the problem instead of the radio?

Finally, I’m not sure how to test the D7 reverse polarity protection diode where the power comes into the radio, nor am I sure that I’m even looking at the right diode. Would I still get 12 volts to the control head if that diode is faulty?

 

[tlemke940]

if the radio is powering up at all i would not think it is d7 if that was bad you would be blowing main fuses. if it still is not powering up it may be a bad chip. are you able to send photos of the deck and head and the connections between them? the only other thing i can think of is swapping heads with a known working one but i don't think you have another one by what i have read so far. can you get into any power on modes (power on radio well holding button 1 next to ch knob {tuning Mode} or hold button 2 next to ch knob{FW Programing Mode}

 

[LostInHertz]

As an update, I sent an email to Blue Mountain Radios this evening as he’s been making some pretty good YouTube videos and I thought he’d be worth a shot at a budget friendly repair if it was a component issue. He immediately spotted an issue with my setup. I thought I had a KCH-11 control head and I assumed the items in my eBay purchase had been a working radio unit at some point in the past. Turns out I that have a KCH-14 (or is it KCH-15?) control head for a TK5710 or TK5810 radio, which isn’t compatible with the TKx90 series. He mentioned that it’s a mistake he’s seen before. For future people reading this, the subtle difference is the KCH11 power button is completely black while the KCH14 and KCH15 control heads have a white half circle emblem on the power button.

The info he provided makes perfect sense for why the radio has no evidence of having a scrambler board or ANI board yet the control head has the emergency button. It was a curiosity that I spotted in the beginning. It’s because it’s the wrong control head for the radio.

I’ll be ordering a KCH11 control head and trying that. I’m hopeful at this point because everything internally on my TK790 seems to be good from all of my testing. I’ll post an update either way after I get a KCH11 so this info is here for future reference for others.

 

[tlemke940]

yep that would do it that's why i was asking for photos but seems like you were already able to find the problem. thanks for the update

 

[mrweather]

eBay strikes again! I swear, these sellers just go in, buy surplus gear and flip them out again without a thought.

The x90 series of mobile radios are built like tanks and will last. Good on ya OP for figuring out the issue.

 

[mmckenna]

eBay strikes again! I swear, these sellers just go in, buy surplus gear and flip them out again without a thought.

No shortage of them showing up here after buying a few pallets of radios and wanting us to tell them what they are and what they are worth. I'm really surprised this doesn't happen more often.