XTS5000 fast running clock

[MTS2000DES]

No, it's not the biggest problem, one of my XTS5000's (700/800 late 2008 build) has a fast running clock. Meaning, even with the radio turned OFF, the time on the clock is usually 20-25 minutes fast. I've checked the little RTC battery, even replaced it (despite the fact the original showed good voltage under load). Radio does not have a UCM installed, and is 100 percent factory, current HOST/DSP loaded via iButton. I don't have any C/P hacks or anything. It's about as "stock" as can be. My other UHF XTS5000 R1 from 2004 and XTS2500 from 2009 have no problem keeping time, even with the radios turned off for days. The only thing different is the 700/800 is used everyday, for 12 or more hours, mostly RX. The other radios are used once a week or so for a few hours at a time. I just can't figure out why the clock runs fast on my 800. anyone have any ideas or encountered this?

 

[Alpha]

Usually RTC chips have their own crystal separate from any other timebases in the unit, and they make many millions of them and they are low frequency, so they are usually fairly inaccurate. Due to this most clocks have a trimmer capacitor to adjust for these discrepancies. I'm not sure in the ASTRO25 series if they have any sort of trimmer but that's where I'd start looking, check the service manual and the schematics to see if the clock has a trim adjustment. A few of the better digital clocks have auto-adjust for the trim, where if you keep advancing the clock due to error it will speed up and eventually adjust itself, but I don't think these are that smart. If there is no trim adjustment, you may just have to replace the clock crystal - there may not be much more you can do.

 

[Mars]

Buying a watch is probably less expensive than the repair

 

[MTS2000DES]

Buying a watch is probably less expensive than the repair

I haven't worn a watch since I was 16. Seriously though, it's not that big a deal just an annoyance. I just went into CPS and turned the clock feature off.
Just makes me wonder if something is slightly off? CPU overclocked? Who knows. Radio works fine and when I had it on the Aeroflex a couple months ago it was dead on, passed all BER tests with flying colors, spot on freq, etc.

Maybe I'll get a stick on clock from the auto parts store! That will get her done. Trailer park fabulous. On second thought, not.

 

[Alpha]

I already said what the problem is; the timebase (crystal) for the RTC (real-time clock) is a separate crystal from the main radio timebase, they are not related. The clock crystal is typically a 32 kHz tiny tubular crystal, and the main radio timebase is a TCXO, a monolithic temperature-compensated crystal and oscillator module. When you adjust the Frequency Warp in tuning, you are trimming the main TCXO timebase, not the RTC one, so that adjustment makes no difference to the clock.

Adjusting some kind of trimmer capacitor or replacing the RTC crystal is the only way to adjust the clock, AFAIK.

 

[MTS2000DES]

I got that, I'm just not motivated to pull the DSM and find out where the trimmer cap is for the tiny little clock XTAL. I guess I should have asked this before going through the trouble of replacing the RTC battery, since it did test good. The radio works fine otherwise. Just a nuisance. Thanks for your explanation. One day when I get bored, I'll pull it apart and report the results.

 

[cyrus]

We've got $10k DS3 muxes that lose at least 20 minutes every month. Makes it hard to correlate transmission problems.

The vendors response was that the engineers bought a cheap RTC from China and we were stuck with it.