Service manual
KB2LJJ Radio Mods Database and Manuals
After having a look at the SERVICE MANUAL i discovered that the audiosignal from the G3RUH should at least be 2 Volts PEP.
This information is not in the original manual delivered with the TM733E.
Txdelay starts at 200mS and combination nr 9 (strap settings G3RUH) seems to be the best to get minimum errors ...
Hoping to set some off you on the right track now...
73 de Jan ON1BJC @ ON4ABG
TTM733 & 9K6
Well John, i'm sorry i have to say this but the Kenwood TM733 is definitely NOT suited for 9600bd operation. It has several serious design
bugs.
● PLL modulation, thereby giving very bad Bit Error Rate figures because of the bad lf response of the modulation circuits. At 64 Hz,
there is a 4.5 dB rise.
● Slow tx<>rx switching. The TM733 needs 100-150 milliseconds to turn around. If your opponent (satellite or earth station) is faster
with replying you keep on missing his first packet.
These problems are very common in the current generation "9600bd ready" transceivers. The Icom IC281/481, Yeasu 5100 and many others
suffer from these problems.
The Kenwood TM733 has another design bug :
● If you try to make more than about 2.5 KHz deviation via the data port, the modulation gets very distorded. This is not easy noticable,
since 9k6 modulation sounds like noise, and distorded 9k6 also sounds as noise.. This problem is seen at more than one TM733,
throughout Europe.
I sure hope you can send this thing back and get your money back, John.
TM-733E MOD 9k6 English
After I bought a Kenwood TM-733E transceiver for packet radio I was very disappointed about the bad modulation in the 9600 baud packet
mode on the 430 mc band. For many digipeaters the tranceiver produced insufficient fm deviation. If you increase the modulation voltage you
will get a strong distortion of your signal. The german Kenwood office was unable or unwilling to fix this problem.
After some experiments I found the following solution for my transceiver:
Increase the internal packet radio modulation signal for the 70cm band by reducing the value of a SMD resistor. The resistor lives on the TX-
RX Unit/Control board (X57-436X-XX)(C/4). The resistor is named R536 and it has a value of 56 kOhm. I reduced itïs value by soldering an
additional SMD resistor of 30 kOhm on itïs top.
The two resistors form a new value of 19 kOhm. This will increase the modulation voltage for the PLL unit and you need less input signal on
the data input at the socket J402. My tranceiver makes now a deviation of 3.5 kHz with 1V/pp instead of 2.2 kHz with 2V/pp before.
There is less distortion than before. Concerning 9k6 packet radio the TM-733E has a bad frequency characteristic. It can be fixed with a
suitable selection of the modem transmission filter. The following selection was the best for my TNC2H:
0 0 1 1 (switches 5 to 8, 1 = up, 0 = down).
Please note:
I am not responsible for your modifications.
You will do it at your own risk!
You need:
15 to 20 minutes time, a magnifying glass a screw driver (X), a needle type soldering iron and a SMD resistor of round about 30 kOhm
1. Remove the top cover ( 4 screws )
2. Remove the bottom cover ( 4 screws )
3. Remove the front panel ( no screws! )
4. Remove the plastic front cover ( 6 plastic snappers )
5. Disconnect the two flat cables on the front board ( shift the bolts )
6. Remove the front board ( 2 screws )
7. Find the SMD resistor named R536 ( the print on the resistor reads 563, it is located on the back side of the front board between the
two flat cable sockets, use a magnifying glass! )
8. Solder the 30 KOhm SMD resistor on top of the R536
9. Reassemble the other way round ( good luck ! )
When the modification is done you have to setup your modem (modulation voltage and filter selection) again.
Concerning Kenwoods bad support in germany my next packet radio tranceiver will be from a different manufacturer.
http://www.kb2ljj.com/data/kenwood/TM-733.htm (2 di 9)30/08/2009 18.42.07