10
If a charge termination fault is suspected, return the charger PCB for replacement as it is not
safe to have the batteries continuously charged. There are four different charge termination
circuits and an immediate recharge prevention circuit: do not attempt diagnosis.
USB faults
Use the AC adaptor to power the unit while attempting to diagnose USB problems.
Many USB problems are actually PC configuration issues. The interface device on the charger
PCB is a USB to serial converter: remote control messages are sent to the main system
processor on the Main PCB through an internal serial link. The counter appears as a COM port to
the PC; this is not a “virtual” COM port it is a real one that happens to be connected by a USB
cable. Port properties such as the baud rate must be correctly configured from the PC end of the
link (details are in the User Manual).
The COM port number allocated is chosen automatically during the driver installation. The BIOS
of some older computers prevents proper operation of a USB connected port if the number
allocated is COM3 or COM4; if this happens, use Device Manager to manually configure it to
COM5 or higher. Note also that some old PC software will not communicate with ports above
COM15.
The interface device on the Charger PCB is responsible for the USB enumeration. If the PC
cannot detect the counter as a USB device, then the fault lies here. The switching logic will not
take power from the USB unless the port has been properly enumerated by the host PC.
If the PC can detect the USB device, but functional control of the counter is not possible then
(provided the baud rate etc. are correctly configured) the fault lies with the processor on the Main
PCB, or possibly on the interconnection between.
Note that changing the USB/Charger PCB will change the instrument’s USB serial number,
so it will appear to be a different unit to any PC, which will seek to reinstall the drivers.
Functional Faults
If there is a fault in any aspect of the operation of the A or B inputs, then the Main PCB should be
returned for repair or replacement.
For a TF960, if operation of the A and B inputs is correct, but the C input is faulty, then further
checks may be carried out to determine the location. It may also be worth checking the soldering
on the interconnections.
Switch on the unit and select the C input.
Note:
if the unit has been dismantled and the Main PCB is hanging loose, take care not to
accidentally press one of the keys and change the operating mode while handling the board.
With no signal applied to the C input, short together the two pins of LK1 on the C input PCB. An
unstable count (broadly in the region of 7GHz) should appear on the display.
If a count appears, then the circuits on the Main PCB are functioning correctly and the fault lies
on the C input PCB. It is possible that the signal detector threshold setting is incorrect. If suitable
test equipment is available, attempt the threshold setting procedure below. Otherwise return the
C input PCB for replacement.
If no count appears, then return both PCBs for repair or replacement.