All, I recently got an (obviously used) Trimble Thunderbolt (case says Rev B). Hooking it up to my bench PS, I got the unit fired up, and the OCXO relatively rapidly settled down to just over 26hz over 10Mhz (According to my Racal-Dana 1992, which I’ve found to be EXTREMELY accurate compared to an Rb and other GPSDO). I thought that meant the PLL had locked, but I’ve since reconsidered since it didn’t take that long (looks like it takes quite a bit longer than that for the GPS to do a survey). Sadly, I couldn’t check the serial connection because I left my adapter at work, so I left it for the night.
Next day, I hooked a serial connection up, and got nothing at all. Checking the TX pin of the unit with my scope, I could see bursts of data, but with less than 1V deviation from the idle voltage level. So, I opened the unit up, and a quick inspection showed me pints 78 and 79 (according to data sheet, those are TDO and +5V) on the Xilinx XC5202 were bridged with solder. That’s odd. Also had obviously been reworked at some point due to the heavy amounts of flux residue around. After finally finding a good image of this area online (http://www.thegleam.com/ke5fx/tbolt/conns.gif), I determined that they shouldn’t be bridged, and fixed that. Powered the unit back up, and still nothing. Also noting that the 5V rail was drawing over 600mA. Finger testing around the board quickly found the RS232 chip (232IBE, now called an ICL232) to be HOT! That it gets so almost immediately after power on. Checking the pins, the +5V and GND for that chip show about 54ohms resistance. I checked the support tantalums and ceramic caps around it, but they all show higher resistance (Keithley 6.5digit meter for the win). So, my questions to all: pull the IC and see if there’s any data showing up on pin 11 or 10 (haven’t traced out which is being used), just replace the chip (I _MIGHT_ have an extra (ICL232, MAX232, etc) in a drawer somewhere), or should I look somewhere else for an issue (shorted Tantalum, etc)? Guess just pulling the chip and seeing if the power draw on the 5V goes down might not be a bad bet either (I do have a hot air rework “gun”). Or just clip/lift it’s 5V pin and see if that resolves the issue. The unit should still lock eventually without that chip. Anything else I might want to check? Thanks all, and thanks Tom Van Baak for the encouragement to test more before posting to the list. =) -Ryan Stasel _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
