Problems and Modifications
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after a short or long time, sometimes 3-30 mins, some other times after several hours
(or days !), all digits of display are "turned-OFF", except the 2 decimal points.
Even if without frequency-display the radio working
normally (on TX & RX).
Remove the upper cover. Now you are looking for the "Control Unit" which leaves behind of Front-panel (see my photos).By using a long & bent terminal for your Volt-meter, check the Voltage on pins 3,4,5 of 74LS247N (Q11,TTL BCD
to 7 segments).
If you measure a LOW logic Voltage, below of 2.5-3 Volts on these 3 pins, the problem
is here from some "cold" solder into PCB.
The correct Voltage on these Pins it must be 4.8 - 5 Volts, in other words just the same with
Pin 16 (+ VCC) of 74LS247.
Be carefull during Voltage measurement, any accident here (ie short-circuit with terminal) should be probably the source for a serious malfunction !
Easy solution: solder a "by-pass" short cable from +5V TP (Test Point) with these Pins, on the upper-side
of PCB. Thus you will save time and hard work, which is necessary to de-assembling the Radio,
in order to be able to remove the "Control Board".
Unfortunately, this PCB is a real garbage! It is not just the very-very bad quality of PCB, but the main problem it's the dozens of passes (holes) between Upper & Down side of double-side PCB, as these "passes" are without "Plated-holes". Thus, the good connectivity from the upper to down tracks depend on the solder. These solder-points through the holes, after several years of operation they seem to be not good enough, especially into the holes which it goes through high enough current, like the +5V TTL feeding voltage.
 Control-Unit Board of TR-9500 (removed) |
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On Rear-panel of TR-9500 you will find the Jack for CW-Key. Even if you connect here a CW-key, the radio is ..denied to transmit on CW ! You need also to connect another Mini-Jack on the 2nd hole of Rear-Panel that is named ST.BY (Stand By). In other words, firstly it should be connected in ST.BY Jack a switch and when that is ON, then it will be lit the "ON AIR" Led on Front-Panel! After that your CW-KEY is ready for transmittion! If you have the original Kenwood's Base for TR-9500 (and TR-9000), this unit including the "SEND" switch precisely for this operation.
Because you... havn't this Base-unit (it's very rare), it's necessary to put on ST.BY a small external Switch. Every time you need the CW-Key in order to send "dashes" & "dots", this switch it must be closed.
Keep in mind that, when the ST.BY switch is closed, the receiver is de-activated and as above mentioned the "ON AIR" Led on Front panel is being lit (see picture below). Under this condition the transmitter is ready, but without Carrier's emission. Carrier on the air you have just when the CW-Key is pushed-down.
If you need an automatic activation of ST.BY, that is possible by using a Timer (ie 555 timer) that it could be activated from CW-Key and it will keep the ST.BY "closed" through a small relay (or switching-transistor) for a short time, ie 0.1-3 Seconds. Thus you will have the well known "Delay", a very common & useful ability on other transceivers.
But if you want a QSK (Full Break-in) operation for CW, it's much simpler. In this case you don't need any SEND switch or Timer. Just connect your CW-Key to... ST.BY Jack (Yes, directly to ST.BY and NOT to the KEY-Jack !). Thus, every time where your Key is pushed-down, you have Carrier "On the Air" ! (..but the internal Relay inside of TR-9500 seems to feel not very comfortable, especially if you are a super fast CW-operator ! As you know under QSK-mode the internal Relay is following your Key, step-by-step ! Bad-news for Relay's health !)
73, Mak SV1BSX
Read also ON4WP's article:
Fixing TR-9000-9130-9500 display boards
Who says technical articles are boring !
There are mainly three possible problems:
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 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
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.... |
see also:
Auto-Doppler Correction for Satellites by using the TR-9500 
to be continued with more Hints & Tips....
