problem: racal 1995 waits several hours before it starts gating - Page 1
Forum section: electronics / general

author: dzhenry
author_rank: Newbie
timestamp: January 24, 2013, 12:23:48 pm
content: I have a 1995 that works well, and I like it, except that from power up to when it starts gating (and counting), can take hours; even if it's been in standby for days. Occasionally I give up when it won't work even after several hours. I always leave it in standby.So if I run a "check" to display the time base, there are no digits in the display, and the "gate" light is on solid when it's failing. Other indicators and controls are OK. Changing resolution does nothing. The "trigger" lights flash normally, and the self test that runs after holding the check button for 5 seconds always passes. Then the counter display blanks. Other measurements seem to work OK.Do these machines have a "typical" failure that can cause this? Any ideas?Thanks, Doug

author: andyb
author_rank: Regular Contributor
timestamp: January 24, 2013, 02:04:59 pm
content: I have a Racal 1992 which has similar symptoms - though not nearly as long. It takes sometimes 30 sec to a min to start from cold power-on, standby start is typically shorter. I've been told that the processor is clocked from the crystal (in my case an OCXO), and I suspect the slow start time is from the crystal not being warmed up yet. I'm also told that even if you use an external frequency reference, the unit boots from the internal crystal. Good luck!

author: saturation
author_rank: Super Contributor
timestamp: January 24, 2013, 02:31:10 pm
content: No inputs work? A, B and I forget, does 1995 have a C too?For some unexplained reason my 1996 Input C began counting strangely then erroneously then wouldn't start for hours; it sounds similar to your, but Inputs A&B were fine. Doing a thorough systems check including a tear down and a PCB go-through found nothing. So I presumed the C prescaler board died.I connected the 10 MHz OUT to the input C to do a cal check and it immediately started and its been fine ever since. It appears like a firmware glitch causing some latch up. Could it be so simple?

author: andyb
author_rank: Regular Contributor
timestamp: January 24, 2013, 02:54:15 pm
content: Hrm, I wonder if this could be a sign of the EEPROM starting to go.

author: lowimpedance
author_rank: Super Contributor
timestamp: January 25, 2013, 12:03:17 am
content: Curious symptoms indeed, thermal issue perhaps.Maybe when it starts working remove the covers and selectsome likely areas to apply some freezer and see if you canlock it up. then let it warm up again (or use a hair dryer) to seeif it restarts. etc.That's if your game to get in there with all the unobtainium andfreezergood luckLowZ

author: grumpydoc
author_rank: Super Contributor
timestamp: January 25, 2013, 01:41:31 pm
content: QuoteThis is certainly true, though when they boot they flash their model number and firmware date code on the display so it would be odd for it to do that, then not count for 30 mins.

author: muvideo
author_rank: Frequent Contributor
timestamp: January 25, 2013, 02:44:28 pm
content: I'd start checking the internal reference output on the rear,if you have another counter or a scope check if the internalreference is alive when the counter is locked. If you have another10MHz source you could connect it to ext reference inputand check if the counter still locks up.You can also check the internal oscillator opening the case,it should have only 3 wires: Vcc,GND and signal.I'd check also the psu voltages and ripple, maybe it'ssimply some capacitor gone, and let's hope it's not oneof these ASICshere the service manual:http://www.ko4bb.com/Manuals/Racal/Racal_1995_1996_Operation_and_Service.pdfFabio.

author: dzhenry
author_rank: Newbie
timestamp: January 26, 2013, 11:19:57 pm
content: Very good ideas and experiences.I will try applying heat and cold to see what I can find.I checked the ref oscillator, and it starts immediately (10MHz output on rear panel), even when the gate isn't happening.Doug