JUMA Amateur Radio Forum

Hi folks.
I've just completed my first serious SMD construction project. My TX-500 powers up OK, and shows the correct S/W version etc (V1.04), but when I press "Oper", the alarms sounds , and it flashes "SWR".
Any suggestions?
Many thanks, es vy 73
John EI7BA

Hello John
SWR alarm means that the control board microcontroller measure some voltage in the REW-PWR analog input. Please see the schematic diagrams and start fault finding by measuring the voltage in the main board REV signal (J3 pin 2). Continue to the control board. Signal same is changed to REW-PWR yet J3 pin 2. REW-PWR signal is pin #33 in the micro controller. Next pin #32 is VDD/+5V. So most probable fault you have is short circuit between pins #33 and 32.

73 Juha oh2nlt

Hi Juha.
Thanks for the info. I checked the REW-PWR line as you said, and indeed there is a problem there. However, the problem is not a short circuit to VDD. I measured about 1.5V on the REW-PWR line, and also on the FWD-PWR line beside it . If I disconnect pins 1 and 2 of J3, it rises to 2.5 V. I was puzzled as to where this voltage was coming from, and after a chat with my friend Ed EI9GQ, I have found the problem... It is the solder flux that I was using. I cleaned the PIC pins with flux remover, and have succeeded in bringing the voltage down to about .5V. I could not get it down to zero volts, so I have put two 15kOhm "pull down" resistors between ground, and pins 1 & 2 of J3.
At last, the buzzer is quiet, and "SWR" no longer flashes. Everything now appears to work as regards control. The keyer works etc, and it goes to TX mode, but there is no RF out. So I have another fault to trace.
Anyway, progress is being made, and I'm learning as I go. One thing I've learnt.. Don't use the telecom linesman's flux..It is conductive!
Many thanks, es vy 73
John EI7BA