Racal-Dana 1992

[staze]

Just got a Racal-Dana off Fleabay, and surprisingly, it works great other than the mushy buttons.

One nice thing is it came with the OCXO, which according to the manual, is stable to 3x10^-9/day (averaged over 10 days, 3 months continuous use), and ±3x10^-9/°C.

This seems, to me, pretty favorable vs. the Gerry Sweeney OCXO hack using this: http://www.isotemp.com/wp-content/uploads/2011/03/OCXO-131.pdf

Though, it does seem that it's nearly an order of magnitude better to use the Isotemp OCXO (0.5ppb vs 3ppb for the OCXO the unit came with). Though, not sure that matters that much for me. Am I missing something?

Other question is, I'd like to fix the mushy buttons. I've seen several posts on it, and it seems the common fix is to use something like these: P12227SCT-ND, then either mod them to have the cross tops, or to mod the buttons (cutting out the fins so they fit on the round actuators). I'd rather do the first option, but I guess Racal-Dana had a fire-sale on buttons when they designed this thing, as it has over 30 of them! Anyone have a good/easy way to do the mod? Someone mentioned heat molding... or use a Dremel. Downside of the former is materials, and the latter is I think the actuator rotates, so cutting it becomes... tricky I would think.

Anyone done either? Have tips?

Oh, unit also came with the battery option (which added a good 2.5kg to the shipping weight, easy). The battery dates to the mid-late 80's... think there's any chance at all it's still usable? I don't overly care, and I've pulled it at this point, but I'd be curious. It's 6 cells, so it's basically a "flattened" car battery. Guess I could just try charging it and monitor the voltage...

[rexxar]

The battery is almost certainly dead beyond any hope. IIRC, aren't they just C size NiCads? You should be able to find replacements easily.

To me, cutting a cross into new switches really isn't worth the trouble. If you're determined to not drill out the original buttons, I guess you could 3D print a cross shape to fit the buttons, and glue that onto a switch with a shorter actuator. Or maybe you could dremel off the actuator from the original switches and glue that on?

I like keeping equipment original as much as the next guy, but that seems like a whole lot of trouble for something as small as buttons. I'd just drill them out, to be honest. 

[staze]

The battery is almost certainly dead beyond any hope. IIRC, aren't they just C size NiCads? You should be able to find replacements easily.

To me, cutting a cross into new switches really isn't worth the trouble. If you're determined to not drill out the original buttons, I guess you could 3D print a cross shape to fit the buttons, and glue that onto a switch with a shorter actuator. Or maybe you could dremel off the actuator from the original switches and glue that on?

I like keeping equipment original as much as the next guy, but that seems like a whole lot of trouble for something as small as buttons. I'd just drill them out, to be honest. 

The battery is lead acid... it's pretty burly.

Cutting off the old actuator and gluing it isn't a bad idea actually. Or if I could find some buttons with really thin actuators, I could just hot-glue (or silicone) the buttons onto those... I just hate destroying the buttons... but yeah, if there's no other good option... not like I'm likely to resell this thing to a collector. I just buy older gear because it's A. inexpensive, B. (usually) easy to repair, and C. Often just as accurate as modern gear for my needs (which are pretty minor).

[lowimpedance]

 I have three 1991's which luckily have good switches, so I have not had a need to do any mods but if I had to I would probably just modify the buttons,.
Make sure you take your time don't rush (not like you will have any spares!).
 One more thing to check when the cover is off and thats the electrolytics - particularly the two 680uF ones as they tend to dry out and the capacitance drops with the result that you will get a frequency reading of the ripple on the display with no input connections!.
 I like Racal counters, underestimated and over looked so good deals to be had for counters every bit as good as HP etal.

[staze]

I have three 1991's which luckily have good switches, so I have not had a need to do any mods but if I had to I would probably just modify the buttons,.
Make sure you take your time don't rush (not like you will have any spares!).
 One more thing to check when the cover is off and thats the electrolytics - particularly the two 680uF ones as they tend to dry out and the capacitance drops with the result that you will get a frequency reading of the ripple on the display with no input connections!.
 I like Racal counters, underestimated and over looked so good deals to be had for counters every bit as good as HP etal.

Yeah, guessing I'd use a scalpel or maybe a dremel very carefully. Just the panasonic switches I guess?

I believe the two 680uF caps were already replaced by a previous owner, as they look like more modern nichicons, vs the wopping 10000uF and 4700uF caps that both appear to be stock from the 80's (have the plastic "cover" over the vent). Always amazed to see things like 10000uF caps in something like this. I think I have some spare 25v 680uF caps I could swap in there just to be on the safe side. They appear (logically) to be the primary filter caps for the ±11.2V rails, with the 10000uF and 4700uF for the ±5V rails.

I do like the counter. Seems very well made (all metal casing), very well laid out, if a bit complex from the front panel. And it's got a nice, readable, bright LED display. No silly VFD or LCD that either wear out, or are unreadable in dim conditions.

Am I better off just leaving it in standby all the time (seems like this keeps the OXCO oven warm)? Almost wish my multimeters had a similar function to keep their references warm, while using minimal power.

Also wish there were better scans of the schematics... whoever scanned them missed the left edge, so they all are missing a bit on the left. But whatever, at least the quality is good (very readable).

[staze]

which height of switches have people used?

[lowimpedance]

Am I better off just leaving it in standby all the time (seems like this keeps the OXCO oven warm)?

If you use the counter on a regular basis you would most certainly leave it in standby as it does keep the oven powered.
But if you only use it occasionally then don't bother, just power it up a day or so before you intend to use it.

One other thing, also be mindful of those smaller local bypass electro's may also be dodgy which can cause instability etc.
Also check under the front end shield to see if the 50 ohm input resistors have been burned by excessive power been applied,
(one of mine had this damage!), and lastly beeee verrrrry careful around those ceramic hybrids break those and its goodnight 1992.
Unfortunately all I have is the operators manual, no service info, but the online version is much more usable than the Keithley 196!!.
LowZ

[staze]

Am I better off just leaving it in standby all the time (seems like this keeps the OXCO oven warm)?

If you use the counter on a regular basis you would most certainly leave it in standby as it does keep the oven powered.
But if you only use it occasionally then don't bother, just power it up a day or so before you intend to use it.

One other thing, also be mindful of those smaller local bypass electro's may also be dodgy which can cause instability etc.
Also check under the front end shield to see if the 50 ohm input resistors have been burned by excessive power been applied,
(one of mine had this damage!), and lastly beeee verrrrry careful around those ceramic hybrids break those and its goodnight 1992.
Unfortunately all I have is the operators manual, no service info, but the online version is much more usable than the Keithley 196!!.
LowZ

All and all, it seems VERY stable, but I haven't left it powered for more than a couple hours at this point. I doubt I'll use it regularly, so I'll just power when needed (well, power a day or so before hand). I largely got it because A. It looked cool, and B. it's a piece of test gear I didn't have. The counter on the Rigol 2000 series is only accurate to 3 decimals that I can see. =/

Just need to do the buttons at this point I guess. =)

[saturation]

The 1992 is a very popular counter and well respected.  To find more about it search the archives for any in the series, 1991, 1992, 1994, 1996, 1998 and 1999.

I have the 1996 and may have a thread on it with many photos.

They key differences are the capabilities of each model year and the 1 GHz option.

The most cost effective Racal Dana 199x series have the OCXO, as the eBay price is on par with none ovens but ovens are tons more accurate.  Beyond an oven, the next leap in accuracy is a surplus Rb oscillator placed on the external port and finally, GPS disciplined, so any in the 199x series will do if you wish an external oscillator.  There is a detailed study comparing oscillator types in the archives, if you need to rationale behind those modalities.

BTW, don't try to adjust the oven oscillator on your Racal unless you have a lot of patience [ days to weeks of time working on it] and a stable Rb oscillator as a standard.

https://www.eevblog.com/forum/testgear/racal-dana-1996-frequency-counter/30/

[g0rsq]

You can find a complete service manual for the 1992 at http://www.ko4bb.com/manuals/index.php?dir=Racal

I also have a scan of a later manual (1987) which is also complete if you are interested.



Regards

Peter

[staze]

still wondering... which height of switches are people using when they do the replacement? Looks like the panasonics are either 9.5mm, or 13mm.