[time-nuts] Trimble Thunderbolt GPSDO Troubleshooting

Robert LaJeunesse lajeunesse at mail.com
Sun Mar 27 11:53:25 EDT 2016


Ryan,

The cap across 1-3 is the one that boosts +5V to +10V, with pin 2 being the +10V result. Thus the pins on this "flying" cap swing 5V p-p (pin 3 is 0 to 5, pin 1 is 5 to 10). The cap across 4-5 is the one that inverts +10V to -10V, with pin 6 being the -10V result. Pin 6 should NOT be at ground. The pins on this second flying cap swing 10V p-p (pin 4 is 10 to 0, pin 5 is 0 to -10). 

Inputs to the transmitter stages (10 & 11) should be at valid logic levels, for the ICL232 these are standard TTL levels. Be aware that other part types that do this same function may not have the same logic levels (Vih and Vil) so be careful when substituting.

I did not mean to suggest lifting pins 10 or 11, although you might consider that last, but pins 7 and 14 should idle near -10V since the transmitter inputs have pullups and the drivers invert. What I was suggesting is to make sure pins 8 & 13 were disconnected [just pull off any RS-232 cable] and look for pins 9 and 12 to be at a good high level, say above 4V or so.

FWIW it's just as difficult to get -12V from +12V via an inverter chip as it is to simply use the ICL232 (or MAX232 or similar) part. Add to that the fact that older high-voltage RS-232 parts tend to be power hungry, and require separate packages for transmitter and receiver. Why use 3 parts when 1 works?

Good luck with scoping out the real problem.

Bob LaJeunesse

> Sent: Friday, March 25, 2016 at 5:33 PM
> From: "Ryan Stasel" <rstasel at uoregon.edu>
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> Subject: Re: [time-nuts] Trimble Thunderbolt GPSDO Troubleshooting
>
> Hi Bob, 
> 
> I think I’m going to take a look, since I couldn’t find a spare, so I’ve got a couple on order (and a few days to wait). 
> 
> So, looking at the datasheet (http://www.intersil.com/content/dam/Intersil/documents/icl2/icl232.pdf), you’re saying check the two caps across pins 1 and 3, and 4 and 5, and make sure they’re swinging. And also check to see if Pin 6 is at “ground” (basically). +V should be at around 10V? Likewise, I’d assume the input to that stage (wherever it comes from) should be a nice logic level input. 
> 
> And then lastly, you’re saying lift/cut pins 10 (and/or 11, depending), and then look at 7 or 14 and see if they’re sitting at 5V (they wouldn’t sit at +10V)? It’s actually kind of funny that they used this chip, since it’s whole point is to eliminate the need for ±12V… except this board specifically has ±12V! =P
> 
> Anyway, I’ll check all this as best I can, or just get frustrated lifting pins, and remove the whole darn thing (like Clint suggested). =P 
> 
> Thanks all! 
> 
> -Ryan Stasel
> 
> > On Mar 25, 2016, at 12:52 , Robert LaJeunesse <lajeunesse at mail.com> wrote:
> > 
> > Personally I'd take a few minutes to look closer at the '232 chip with the scope. Are the charge pump caps swinging 5V p-p and 10V p-p? if not swinging at all, trash the chip. Is -V pin voltage about equal to the negative of the +V pin? If so, that's OK. If not might have an output shorted, or a bad chip. Is the +V pin about +10V?  If so, that's OK. If not might have an output shorted, or a bad chip. With no RS232 driving source connected does the receiver output look like a valid 5V logic high level? If not, look for a short on this line. If all these pass and the chip gets hot, replace the chip.   
> > 
> > Bob LaJeunesse
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