Racal Dana 1992 teardown - Page 1
Forum section: electronics / general

author: muvideo
author_rank: Frequent Contributor
timestamp: February 14, 2012, 10:39:24 pm
content: Hello,recently I won the auction on two Rb frequency standards, no real need of them,I just bought these because I was curious and the cost was very low.Too many times I burn money on things that I don't really need, worse usually thesethings need repair or cleaning and I burn an huge amount of time trying to find use forthem, repairing etc..., and usually these things need other things and so on...(edit: this time I was very happy with the results, more to follow)Anyway I started thinking how to use these clocks, and started searching for a decentlow cost frequency counter. My purpose was to use the Rb clocks as timebase for thecounter, so my only need was a decent resolution.And here is it, the Racal Dana 1992, it arrived in "as is" state, the seller only assured methat the counter would power on, no mention of options, not able to test it.When It arrived, I changed the voltage setting for european voltage, attached a powercord and started the thing, being careful to not touch with bare hands the metal case,you never know...It came to life showing model number, some other things and after random numbers.The first thing I noticed was that part, almost half, of buttons were not responsive.I had read about these faulty switches previously, so I started to tear down this equipment.The first thing I noticed after opening the case was the beauty of construction, all metal,very simple and rational, a pleasure to see, so I started taking pictures.More to follow...

author: muvideo
author_rank: Frequent Contributor
timestamp: February 14, 2012, 11:01:46 pm
content: Ok let's open it...

author: muvideo
author_rank: Frequent Contributor
timestamp: February 14, 2012, 11:10:28 pm
content: Now the problematic part: the switches, first the board dismantled,after a closeup of switch dissected.Seems that the usual conductive rubber fails, the switches measurefew kohms closed.

author: muvideo
author_rank: Frequent Contributor
timestamp: February 14, 2012, 11:21:15 pm
content: A local seller has the usual cheap pushbuttons, I'm thinking to modify themas follow, if someone knows a better way let me know.

author: muvideo
author_rank: Frequent Contributor
timestamp: February 14, 2012, 11:26:51 pm
content: And now the interesting part, if I understand correctly I was lucky to find ina OCXO, The racal dana 9462 oscillator is a 5MHz high stability ovenized,doubled to 10MHz.Should be equivalent to option 04E, if someone knows more please shareinfo.Edit: stupid I am, it was written on a big label on the side of the instrument:1992/02M/04EHere is it...

author: tinhead
author_rank: Super Contributor
timestamp: February 14, 2012, 11:40:43 pm
content: you will find here user/service manual/schematics and option descritionshttp://www.ko4bb.com/manuals/index.php?dir=RacalBtw, when you have a chance make a dump of the EPROM and upload to ko4bb.com incoming,this might help other ppl to repair their old gear.

author: muvideo
author_rank: Frequent Contributor
timestamp: February 15, 2012, 06:26:50 pm
content: After some hours of work, I swapped all the switches,tested the basic self tests and all passed. I connectedone of the Rb clocks to input and it readsthe 10MHz frequency with less than 0.2Hz difference,so there is a high probability that the OCXO is fine.Now I have to build the psu for the rb clocks andmount them in a suitable box.More photo to follow.Quote from: tinhead on February 14, 2012, 11:40:43 pmThank you tinhead for the links, now I don't have an eprom reader, when I'll have thepossibility I'll extract and upload the firmware.Fabio.

author: IanJ
author_rank: Unknown
timestamp: February 15, 2012, 08:55:28 pm
content: Hi,Wow!....a Racal Dana 1992.... I used to use one of these back in the late 80's.....really great to see one again.Thanks for posting.Ian.

author: muvideo
author_rank: Frequent Contributor
timestamp: February 25, 2012, 01:19:44 pm
content: Quote from: IanJ on February 15, 2012, 08:55:28 pmI'm happy you liked it, it seems a fine instrument for it's age,later i'll upload some photos of it measuring a pair of Rb oscillators.Fabio.

author: muvideo
author_rank: Frequent Contributor
timestamp: February 25, 2012, 01:52:07 pm
content: A little update:for the last 10 days I left it powered, in the mean timeI found an home for the two FE5680A Rb oscillators I boughton the bay.When I shoot these photos the Rb oscillator were powered froma pair of days, the measurements are with 10 seconds timebase,the display shows the last 9 digits, the first two digits "10"are on the left not shown by the display. The least significantdigit shows mHz of the 10MHz signal.The first photo is the highest frequency Rb measured using theslowest one as timebase, the difference is 15mHz.Other two photos show the frequency of the two Rbstandards measured using the internal oscillator.The last 3 photos show the highest Rb standard measuredfrom different positions of the meter, is the earth magneticfield or the gravity?Edit: -------reading around, the internal oscillator that is quartz basedis acceleration-sensitive, the Rb Standards should be moresusceptible to magnetic fields, and less influenced by acceleration.So the frequency shift should be from gravity acceleration.--------------Not bad from a (more than) 20 years old instrument, I was impressedby the small frequency difference, I don't know the absolute error from true10MHz , but I suspect that all 3 are very close to the real frequency.Fabio.Edit: I had previously indirectly measured the frequency difference of the2 Rb oscillators using a dso: one on the frist channel and the other on thesecond, it took about 60seconds for the two waveforms to return to the same phase.

author: SeanB
author_rank: Super Contributor
timestamp: February 25, 2012, 02:50:11 pm
content: Nice unit, looks like it was made in 1989.I used to use an older Racal Dana 6 digit multimeter, was made in the 70's, had a 7 segment filament display. Slow conversion rate ( 1 per second) and loud autoranging relays, but it just worked.

author: im_a_human
author_rank: Regular Contributor
timestamp: February 25, 2012, 07:38:45 pm
content: I had one of these Frequency counters up to about 3 years ago. I bought it second hand back in 1993. I had to replace all the switches as they had a habbit of packing up after a few years.

author: T4P
author_rank: Super Contributor
timestamp: February 26, 2012, 05:53:28 am
content: Quote from: SeanB on February 25, 2012, 02:50:11 pmYou mean nixie tube displays don't you ?

author: muvideo
author_rank: Frequent Contributor
timestamp: February 26, 2012, 07:35:11 am
content: Quote from: Dave.S on February 26, 2012, 05:53:28 amI don't know the racal multimeters but I have somewere in the "strange things bin" some 7 segments incandescent displays.Fabio.

author: lowimpedance
author_rank: Super Contributor
timestamp: February 28, 2012, 12:33:49 am
content: Racal made some nice test gear particularly when they acquired Dana (thus Racal Dana).Generally not sought after on the second hand market, so can be picked up cheap.Besides the switches you should check C52 and 59 both 680uF electro's they have a tendency to dry out.A give away is a display of the rectified mains frequency with no input (100hz or 120hz for those on 60hz).Also check the 50 ohm (100ohm//100ohm) on each input to make sure someone has not connected a transmitterand toasted them!!.I have a couple of the 1991 counters, and the oven oscillator was rare, most likely a 10Mhz TCO.Worked for them early eighties.cheersJohn

author: muvideo
author_rank: Frequent Contributor
timestamp: February 28, 2012, 09:39:05 am
content: Quote from: lowimpedance on February 28, 2012, 12:33:49 amThank you very much John, I'll check these components.So you worked for Racal?Reading around seems that these 1992/02M are from (large?) military contract,and are all with this 04E oven oscillator.Fabio.Edit, for the record if anybody need them, I uploaded the ROMS onhttp://www.ko4bb.com/manuals/as of 16/may/2012 they are in recents directory, in few days they will be checked and putprobably under ROM directory.

author: slburris
author_rank: Frequent Contributor
timestamp: September 10, 2012, 04:06:42 am
content: What switches did you use to replace the failing ones? I haveA Racal Dana 1998 counter and many of its switches havebecome mushy and don't spring back anymore. Looking atthe service manual it's the same switch as one the 1992.I can't seem to find any 2pin switches of the proper type.Scott

author: muvideo
author_rank: Frequent Contributor
timestamp: September 10, 2012, 07:16:09 am
content: Quote from: slburris on September 10, 2012, 04:06:42 amHello Scott, I used normal 4 pin 6mm square tactile switches,size like these ones ebay #180909689661.Just cut away two pins, they will fit in the holes.They are working ok, the only small defect is that are a little"bouncy".Here you can see what I've done:Fabio.

author: grumpydoc
author_rank: Super Contributor
timestamp: September 10, 2012, 12:49:01 pm
content: Or something likethese switchesfrom Farnell/Element 14I needed to do just one on a 1998 which is working perfectly now. I think muvideo cut the actuator into a cross to fit the switch - I drilled out the switch to fit the actuator.

author: muvideo
author_rank: Frequent Contributor
timestamp: September 10, 2012, 02:00:30 pm
content: Quote from: grumpydoc on September 10, 2012, 12:49:01 pmYes I used a brass plate with a cross cut, insterted it into a soldering iron and used it as "hot die",after some regulation found the right temp to do the work.Tried drilling the switch caps but didnt like the result.Fabio.

author: grumpydoc
author_rank: Super Contributor
timestamp: September 10, 2012, 03:13:36 pm
content: Undoubtably the best approach - after all if you destroy one of the new switches it's no great problem. the switch caps themselves are rather less replaceable.I tried this but found the actuator too small and fiddly to cut and wouldn't be able to reproduce a hot die at all so didn't have much choice.

author: free_electron
author_rank: Super Contributor
timestamp: September 10, 2012, 09:45:09 pm
content: holy moly, that's a bucket of unobtainium parts ....I see an asic from AMCC ... a hybrid module next to it and a custom botch from Plessey nonetheless...7218 for display scaning an a 74922 for the keypad scanning...

author: slburris
author_rank: Frequent Contributor
timestamp: September 11, 2012, 03:22:11 am
content: I ran across a reference to someone using this Panasonic switch, which isP12227SCT-ND at Digikey. Looks promising, although you still have to cutthe shaft to fit the keycaps.I'm not sure how best to fabricate the cross cut. Maybe it's possible todo a passable job with a dremel and some silicone adhesive in the keycap?It just makes me really mad that such useful counters are rendered uselessby such a stupid problem. I had hoped that the 1998 counter would not havethe same problems as the 1992.Scott

author: slburris
author_rank: Frequent Contributor
timestamp: September 11, 2012, 03:35:13 am
content: I picked up this little beauty on Ebay a few months ago.It's a 5Mhz OCXO with a doubler board to make 10Mhz.I think it was a pull from a 1992 counter, but it drops rightinto my 1998 counter, replacing the standard TCXO.Normally, I don't care too much about the internal oscillator, sinceI use a Trimble Thunderbolt to generate a house 10Mhz standardand run that to all my test equipment which can take anexternal reference. But since this is my go-to counter, Iwanted to be as accurate as possible when I take it with mesomewhere.I've got an HP5328A, but it's such a noisy beast, I almost neveruse it (until now, since my 1998 developed its switch problem).Scott

author: grumpydoc
author_rank: Super Contributor
timestamp: September 11, 2012, 07:22:03 pm
content: Hmmm, I think I spotted that one - wish I'd had my Crystal Ball working though because I didn't buy it and I've now just acquired a 1992 that locked up after a few minutes use - turned out to be a faulty TCXO.Odd that I should have two pieces of equipment have oscillator modules which failed in the same way (stopped when "warm") within a couple of weeks of each other. C'est la vie, I suppose!

author: slburris
author_rank: Frequent Contributor
timestamp: October 06, 2012, 05:09:35 pm
content: And now I've acquired a 1992 to go with my 1998.The seller said powers on unable to test. Which we all knowIs code for "I powered it up and something's wrong with it"I expected to get a counter with a bunch of bad switches but thatdoesn't appear to be the case here. It does seem to have issues though.I applied the output of a signal generator to the A input and oddlythe trigger lights for both A & B flash. The counter displaysThe correct frequency. But I can't seem switch the mode of the counterAnd none of the freq/period/total/phase etc LEDs are lit. The resolutionbuttons work fine.So it's sort of working. Do these symptoms sound familiar to anyone?I may see if there's an EPROM image out there to check if I have bit rot.Otherwise time to break open the service manual.Scott

author: grumpydoc
author_rank: Super Contributor
timestamp: October 06, 2012, 05:15:43 pm
content: The B channel trigger LED flashing with a signal applied to the A channel seems to be normal - with no input the AGC is wound to max gain and it's either noise or possibly coupling from the A channel.Not being able to change the mode is probably bad tactile switches on the two buttons in question, have you tried all the other buttons.Where are you located?

author: slburris
author_rank: Frequent Contributor
timestamp: October 06, 2012, 05:41:25 pm
content: I'd expect the FREQ A LED to be lit at power on, at least based on experience with my 1998 counter.I pressed all of the buttons. None seem to have the squishy feel of failed buttons but I suppose it could be another kind of switch failure other than the rubber dome problem.I'm in the US.Scott

author: muvideo
author_rank: Frequent Contributor
timestamp: October 06, 2012, 05:44:32 pm
content: Can be noise, and there is also the COM A button that connects B input to A input,maybe that is engaged in some way? Also I would check the buttons with a dmm,maybe some is stuck closed.My roms are here:http://www.ko4bb.com/manuals/index.php?dir=04)_ROM_Images_and_DriversFabio.

author: slburris
author_rank: Frequent Contributor
timestamp: October 07, 2012, 12:36:41 am
content: Well this is most peculiar. After power cycling a few times all of the issues seem to have magically cleared up. I hate it when problems mysteriously go away. Maybe some marginal electrolytic capacitors inside?Still I wasn't expecting a working unit for $100. I connected the output of a Trimble Thunderbolt to it and after warming up for 30 minutes it reads 10MHz +- 2 digits.I have an OCXO in my 1998. I think I'll move it to the 1992 ( and look for any bulging caps while I'm at it).Scott

author: Smokey
author_rank: Super Contributor
timestamp: August 30, 2024, 05:02:55 am
content: I made a silly ebay "make an offer" on a 1992 and the dude accepted it. Didn't expect thatAfter replacing all the switches I noticed the reference was surprisingly good. Turns out it's a "04E High-Stability" oven. Cool.Option 04E High Stability Ovened OscillatorFrequency: 10 MHzAging Rate: ≤ 5 x 10^-10/day at shipment averaged over 10 daysTemperature Stability: ≤ 7 x 10^-9 over the range 0°C to 50°CLine Voltage Stability: ≤ 5 x 10^-10 two minutes after a 10% line voltage changeHow good is that relative to modern references?