Well, my
After last repair, I noted there were some trouble with the ON AIR indicator, as it sometimes didn't follow the PTT: from time to time it kept lit even in RX and also the opposite (off on TX). I found also some other problems.
Summing up this is what I had found:
Thanks to my friend Mario EB5HRZ, I got on the bench another TS-790 to be able of doing some side-by-side checks.. and, yes, if I swapped CONTROL UNITs from one 790 to the other, the problem followed the CONTROL UNIT. So at least I was sure the fault was on it!
Then I checked signals at the CPU. RESET signal worked exactly the same in both. Oscillators were also the same, starting immediately after power on. But all the I/O activity seemed frozen in the bad unit, until about 5 seconds passed. Checking control lines at the CPU, there was one long delay since first WR signal was generated until the next ones, in the bad CPU, but none in the good one (I mean WR signal was switching fastly on good CPU, since first moment)
I checked voltage rails with oscilloscope, and were perfect.
It seemed there was some problem in the data bus as, what happened when LEDs did weird things is that the command from the main CPU to the display CPU had some error on it so it was interpreted as another commmand. In fact, when for example LOCK LED was lit during tuning, frequency on display remained the same but there was a change in frequency. So I guessed display refresh command was corrupted and the damaged transmission was interpreted as another command.
Next day, I continued with the CONTROL BOARD resoldering I started the day before. It took about 2 hours to get it done completely.
But then, after reassembling it in the rig, it did not power up, even waiting for the 5 seconds it used to take :-(. Well, I was sure there were no soldering bridges in my work (it was done with lots of care and I am soldering since I was 9.. now I am 40 ;-)!) so I thought what happened is that something was now worse than before, reinforcing the idea of a soldering or PCB trace problem.
While I was measuring with the oscilloscope, finding that CPU clock oscillated and there was address and data I/O from the CPU, it suddently came back to life, but with the same old problems (LOCK LED lighted from time to time when rotating dial and such). I powered it off again and then I got a silly idea.. my guessing was that the problem could reside in some input to the CPU which was waiting for something to be ready.. so I carefully touched with my finger around the CPU pins.. and rig came back to life again!
Looking at the schematics they were all signals to and from (!) the fluorescent display (FIP). I fastly reduced the focus to the FIP BY signal (pin 4 of the CPU). It was low on start up and, as soon as it got high, rig started to work. And, yes, placing a 1k pull-up was enough for the rig to power up always immediately :-)!!!
JOSEI recently got a second hand TS-790 with the 1.2 GHz unit installed and after a good cleaning and service I've done, I decided to search the options I have to get the IF from the radio to feed my SDRplay wideband receiver.
There is no doubt that software defined radios are the future.. I thought it would be very nice to have a panoramic view of the bands while using the same antenna.
After search I found the TS-790 service manual and I started to study it. This rig has 2 independent receivers (main and sub) and as a result has also 2 IF's. The IF for the main receiver is 10,695 MHz and the IF for the sub receiver is 10,595 MHz.
I decided to go for the sub band IF because I didn't wanted to mess with the transmit circuits used in the main band. Looking at the block diagram it seems that the signals from all the bands (VHF/UHF/SHF) are going into the XF1 filter and then to Q5 fet amplifier. So the best place to tap for the IF would be the drain of Q5 fet. Respectively, if someone wants to get the IF from the main band should look for the drain of Q56 fet.
At the schematic diagram below you can see the exact tap point. Sorry for the bad quality of the pictures, but the scanned service manual is very bad..
Of course, you can't just solder a simple wire and get the IF. You need to add a suitable buffer amplifier to isolate you from the circuit and that way you don't have losses at your sub receiver.You have to use a good quality RF cable and place the buffer amplifier as close as you can to the tap point.
You will also need to get somewhere the 13,8 volts to give power to the buffer amp. You can build your own buffer or you can buy one, as I did. I chose to buy from G4HUP.
There is a lot of work needed to actually reach the IF tap point. If you feel that you cannot do it, then DON'T TRY IT. You may damage your expensive radio. Ask for help from someone that is more qualified to do this.
I take no responsibility for any damage that this modification may do to your radio. Proceed at your own risk !!!
Remove the bottom cover of your radio. You will see the IF board. Then you have to remove the IF board. To do that you must unscrew first all the screws keeping the board in place and also unplug all the cables. There are many cables !!! It's highly recommended to take a high resolution photo of the board with all the cables attached in case you forget their position.
Then locate the IF tap point. In practice I soldered the cable directly to the L3. I find it's a good place and not very risky to burn the FET or other components. Don't forget the shield of the coax, use as ground the case of L2. Use a good quality RF cable. Secure the cable to the board with some tape. Check my photos below. (G4HUP does not provide the input RF cable, he provides only the output IF cable with a male or female SMA connector). I got the male SMA option to connect direct to the SDRPlay receiver input.
You will also need power for your buffer board. A good and safe place is the pin 7 of the ACC 4 connector. It's at the back side of the board, a little far, but I didn't have any RF problems. This pin provides 13,8 V from the main power switch of the radio. If you search carefully you may find a closer place to get the power. I was in a hurry to test this mod, so I didn't searched more :-)
The buffer board is secured with double side tape on the chassis at the front. For easy installation, the IF output cable is routed on the top of the board, however you can route it from the bottom. Use tireups to secure the cable from moving front and back.
By using the tap point at L3 you will only have a maximum usable bandwidth of about 50 KHz because of the filter on all bands (V/U/S).
If you want to see more bandwidth at your waterfall, you can try a different tap point at L1. This will give you at least 1 MHz (and much more), which in some cases might be more usefull.
If you go up to the top of the page you will see at the IF schematic diagram a GREENpoint. This is L1. Click on the picture below to see in detail my second test with the tap point at L1.
Don't try to get the IF without a buffer amplifier - isolator, or you will loose RX sensitivity and maybe damage your radio. This is NOT recommended and NOT guaranteed.
I think I'll stay with the second solution for maximum bandwidth, it makes more sense to me for my needs and works good. I have tested the VHF band and the results are excellent. Same performance on receive and almost 2 MHz (and much more) of bandwidth at my waterfall. But please have in mind that tapping at L1 will NOT give you more bandwidth at UHF and SHF bands, since the signal coming from the 430 and 1200 RF boards is filtered before. If you want more bandwidth at these bands you have to tap to the RF boards. I didn't do it because I'm mostly interested at VHF band.
So many options and a totally new way to enjoy my radio and hobby..
73, Fanis
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- Kenwood Ts-790 Service Manual Posted on 1/7/2018 by admin Title: Kenwood - TS790 User manual Author: Unknown Subject: Dual band RTX Keywords: Kenwood - TS790 User manual Created Date: 0.
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has given me some more problems.. read on to see how I got through them!After last repair, I noted there were some trouble with the ON AIR indicator, as it sometimes didn't follow the PTT: from time to time it kept lit even in RX and also the opposite (off on TX). I found also some other problems.
Summing up this is what I had found:
- Variable delay to power up display and keypad input from POWER ON: from 2 to about 5 seconds.. and getting worse!
- Inconsistent ON AIR indicator (sometimes it does not follow PTT!)
- LOCK LED lights from time to time while changing frequency (but LOCK is NOT activated)
- DISPLAY refresh fails: frequency changes in the unit but change is not displayed.
Thanks to my friend Mario EB5HRZ, I got on the bench another TS-790 to be able of doing some side-by-side checks.. and, yes, if I swapped CONTROL UNITs from one 790 to the other, the problem followed the CONTROL UNIT. So at least I was sure the fault was on it!
Then I checked signals at the CPU. RESET signal worked exactly the same in both. Oscillators were also the same, starting immediately after power on. But all the I/O activity seemed frozen in the bad unit, until about 5 seconds passed. Checking control lines at the CPU, there was one long delay since first WR signal was generated until the next ones, in the bad CPU, but none in the good one (I mean WR signal was switching fastly on good CPU, since first moment)
I checked voltage rails with oscilloscope, and were perfect.
It seemed there was some problem in the data bus as, what happened when LEDs did weird things is that the command from the main CPU to the display CPU had some error on it so it was interpreted as another commmand. In fact, when for example LOCK LED was lit during tuning, frequency on display remained the same but there was a change in frequency. So I guessed display refresh command was corrupted and the damaged transmission was interpreted as another command.
Next day, I continued with the CONTROL BOARD resoldering I started the day before. It took about 2 hours to get it done completely.
But then, after reassembling it in the rig, it did not power up, even waiting for the 5 seconds it used to take :-(. Well, I was sure there were no soldering bridges in my work (it was done with lots of care and I am soldering since I was 9.. now I am 40 ;-)!) so I thought what happened is that something was now worse than before, reinforcing the idea of a soldering or PCB trace problem.
While I was measuring with the oscilloscope, finding that CPU clock oscillated and there was address and data I/O from the CPU, it suddently came back to life, but with the same old problems (LOCK LED lighted from time to time when rotating dial and such). I powered it off again and then I got a silly idea.. my guessing was that the problem could reside in some input to the CPU which was waiting for something to be ready.. so I carefully touched with my finger around the CPU pins.. and rig came back to life again!
I was able to do this several times and found a zone of about 4-5 pins which consistently started the rig when touched.. suspicious, right ;-)?
Looking at the schematics they were all signals to and from (!) the fluorescent display (FIP). I fastly reduced the focus to the FIP BY signal (pin 4 of the CPU). It was low on start up and, as soon as it got high, rig started to work. And, yes, placing a 1k pull-up was enough for the rig to power up always immediately :-)!!!
Of course, even with the pull-up, rig continued to produce random problems.. but I knew I was close!. So I traced that control line to the connector which go to the DISPLAY BOARD and, yes, there was no continuity :-)!!!. I tried to find the faulty via but as it goes below the CPU itself and the service manual PCB is not clear enough on that zone to follow the trace, I decided to run a tiny wire (wire wrapping kind) from the CPU pin to the connector, fixing it as it was made in the old PC mainboards, with small drops of adhesive spread along the wiring route (tape is only until adhesive cures)
And, YES!!!, rig started AND behaved perfectly on next power-ups.. so it was FIXED!!!
Wow, how great is to find an obscure fault :-)!
Thanks you all for the patience to read all these ramblings. I hope they could help in the future to some other troubled TS-790 users.
Best regards from a very happy camper,
JOSEI recently got a second hand TS-790 with the 1.2 GHz unit installed and after a good cleaning and service I've done, I decided to search the options I have to get the IF from the radio to feed my SDRplay wideband receiver.
There is no doubt that software defined radios are the future.. I thought it would be very nice to have a panoramic view of the bands while using the same antenna.
After search I found the TS-790 service manual and I started to study it. This rig has 2 independent receivers (main and sub) and as a result has also 2 IF's. The IF for the main receiver is 10,695 MHz and the IF for the sub receiver is 10,595 MHz.
I decided to go for the sub band IF because I didn't wanted to mess with the transmit circuits used in the main band. Looking at the block diagram it seems that the signals from all the bands (VHF/UHF/SHF) are going into the XF1 filter and then to Q5 fet amplifier. So the best place to tap for the IF would be the drain of Q5 fet. Respectively, if someone wants to get the IF from the main band should look for the drain of Q56 fet.
Kenwood TS-790 IF Block diagram |
KENWOOD TS-790 Schematic with SUB IF TAP POINT |
Of course, you can't just solder a simple wire and get the IF. You need to add a suitable buffer amplifier to isolate you from the circuit and that way you don't have losses at your sub receiver.You have to use a good quality RF cable and place the buffer amplifier as close as you can to the tap point.
You will also need to get somewhere the 13,8 volts to give power to the buffer amp. You can build your own buffer or you can buy one, as I did. I chose to buy from G4HUP.
There is a lot of work needed to actually reach the IF tap point. If you feel that you cannot do it, then DON'T TRY IT. You may damage your expensive radio. Ask for help from someone that is more qualified to do this.
I take no responsibility for any damage that this modification may do to your radio. Proceed at your own risk !!!
Remove the bottom cover of your radio. You will see the IF board. Then you have to remove the IF board. To do that you must unscrew first all the screws keeping the board in place and also unplug all the cables. There are many cables !!! It's highly recommended to take a high resolution photo of the board with all the cables attached in case you forget their position.
Then locate the IF tap point. In practice I soldered the cable directly to the L3. I find it's a good place and not very risky to burn the FET or other components. Don't forget the shield of the coax, use as ground the case of L2. Use a good quality RF cable. Secure the cable to the board with some tape. Check my photos below. (G4HUP does not provide the input RF cable, he provides only the output IF cable with a male or female SMA connector). I got the male SMA option to connect direct to the SDRPlay receiver input.
IF TAP POINT DIRECTLY TO L3, SHIELD TO L2 |
You will also need power for your buffer board. A good and safe place is the pin 7 of the ACC 4 connector. It's at the back side of the board, a little far, but I didn't have any RF problems. This pin provides 13,8 V from the main power switch of the radio. If you search carefully you may find a closer place to get the power. I was in a hurry to test this mod, so I didn't searched more :-)
13.8 V from power supply |
Buffer board in place |
General view of the IF board with buffer installed |
If you want to see more bandwidth at your waterfall, you can try a different tap point at L1. This will give you at least 1 MHz (and much more), which in some cases might be more usefull.
If you go up to the top of the page you will see at the IF schematic diagram a GREENpoint. This is L1. Click on the picture below to see in detail my second test with the tap point at L1.
Don't try to get the IF without a buffer amplifier - isolator, or you will loose RX sensitivity and maybe damage your radio. This is NOT recommended and NOT guaranteed.
IF tap point before the filter (at L1) for maximum bandwidth |
Kenwood Ts 590s Manual
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My favorite SDR software is HDSDR. It's free and easy to use. Configuration is very easy. Just set the IF frequency to 10.595 MHz and start listening !!!HDSDR IF CONFIGURATION |
Programming Kenwood Tk 790
Of course there some other options needed to be set, but this is out of the scope of this guide. For example you can set the software to control your TS-790, sync frequencies in both directions, etc.. There are many tutorials online, just search them. And there are other software packages available, such as SDR Console, SDR# and others.So many options and a totally new way to enjoy my radio and hobby..
Kenwood Ts 790s
73, Fanis