That 232 chip should run at near as damnit ambient so I'd say it's highly likely to be dead.
Replacement should be a doddle On 25 Mar 2016 19:02, "Ryan Stasel" <[email protected]> wrote: > 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. > _______________________________________________ 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.
