Racal Dana 1992 locks up - Page 1
Forum section: electronics / repair

author: Squiddaddy
author_rank: Regular Contributor
timestamp: February 19, 2018, 06:49:58 pm
content: I have an issue with my Racal Dana 1992 counter.Just recently, it started locking up randomly while taking readings. That seems to have gotten better.It also locks up when going into standby, and will not recover unless power cycling the unit.I haven't used it in a while, and it just started. Bought it about 2 years ago.My garage is not heated unless i'm in there working, so I'm not sure if it was temp related.But it's pretty repeatable now, even with the garage warmed up.I have the service manuals, but I'm not exactly sure where to begin looking. Nothing on the flow charts about lockups.I may try to remove and reseat the CPU and OCXO, in case it's a dirty socket.Power supply voltages look good, and the unit is still very accurate compared to GPSDO.All performance tests in the manual pass.Anyone else ever had this issue, that can point me in the right direction to troubleshoot, so I'm not wandering?Thanks!!

author: perdrix
author_rank: Frequent Contributor
timestamp: February 19, 2018, 07:02:58 pm
content: I don't know how helpful this will be, but a while back I had the most annoying intermittent problem with a 1998, that I eventually traced to an SMD resistor on the underneath of the board that was only soldered on one side. Most of the time it had worked by contact with the pad, but as time wore on ... As it worked as a pull-up (or pull-down - I can't remember), when it didn't make contact, things went to pot.So take a good looksee at the under-board mounted SMDs to see if you have a similar problem.

author: lowimpedance
author_rank: Super Contributor
timestamp: February 19, 2018, 11:16:27 pm
content: Even if the supplies look good I would fully recommend replacing the electrolytic caps, particularly the 680 uF ones. There have been quite a few threads in relation to the 1992 and the 1991 counters here.One other thing to look out for besides the caps drying out is the front panel switches failing which may cause locking up.

author: Squiddaddy
author_rank: Regular Contributor
timestamp: February 20, 2018, 02:17:45 am
content: I have not changed any caps yet. I do have new switches, for when these fail. Are you saying that even though they still work and feel ok, that they can cause issues? Counter worked great last summer when i repaired a Tek 2235 scope.I will order those caps since everyone seems to recommend that.I will also check the ocxo connection, since that runs the cpu.

author: lowimpedance
author_rank: Super Contributor
timestamp: February 20, 2018, 02:21:34 am
content: If the keys feel okay then leave them alone for now. While others have reported switch issues I have not found any such problems with my 1991's , but have certainly had capacitor problems.

author: pigrew
author_rank: Frequent Contributor
timestamp: February 20, 2018, 03:07:35 am
content: I've read that the Racal 1992's CPU is clocked directly from the 10 MHz oscillator. Can you double-check that the oscillator is running (by probing the REF OUT port on the back)?

author: Squiddaddy
author_rank: Regular Contributor
timestamp: February 20, 2018, 04:20:35 pm
content: The oscillator is running. It's option 4E the high stability one. It's very accurate, as I just got a TruePosition GPSDO board and started testing that. Still has the cal sticker over the adjustments. I can check it's connection and make sure it's not loose.I read lowimpedance's thread where he had one that locked up after it sat for months, which is just like I'm seeing.So I guess I need to do the capacitors since it's old, and check for loose connections, since the chips are socketed.I just don't want to damage it, so I wanted to ask if there might be something simple to start with and not go down the wrong path.That's why I haven't done the switches yet, they still feel ok.Thanks for all of the comments guys! I appreciate the help.

author: edpalmer42
author_rank: Super Contributor
timestamp: February 20, 2018, 04:53:30 pm
content: If you have a temperature probe, check the temperature of IC39. It's a custom ASIC that runs hot. I've seen a couple of 1991/1992 counters where that IC failed. I remember that one of them was running at ~90C after it failed. Normal temperature is something like 60C, I think. That IC can't be replaced so, if it fails, the counter is scrap.Ed

author: Squiddaddy
author_rank: Regular Contributor
timestamp: February 20, 2018, 08:47:09 pm
content: I will check that also. And I think I may try to heatsink that chip. Surprised Racal didn't do that.The counter has changed some since I started this post. It hasn't been locking up after power on anymore, but it still gets stuck in standby. If I put it in standby, it no longer responds to the key to wake it up, and I have to power cycle it. But I used it for several hours last night monitoring an OCXO. My concern is if I don't use it for several weeks again, will I end up right back with the same issue?But I will take the advice here and work on the known items like caps, dirty sockets, etc.Excellent comments everybody!!

author: lowimpedance
author_rank: Super Contributor
timestamp: February 20, 2018, 11:11:07 pm
content: Quote from: edpalmer42 on February 20, 2018, 04:53:30 pmGood point about that IC, it most certainly gets toasty !. I have actually made a heat sink arrangement for one of mine that gets used the most. A bit 'Heath Robinson ' but it does the job.See pic. below. Also bonus factory bodge wires. Does your 1992 have those too ?.

author: Squiddaddy
author_rank: Regular Contributor
timestamp: February 21, 2018, 12:29:43 am
content: Looks like a fairly simple heatsink.Mine only has one bodge wire on the back of the display. None on the main board.Running it a while again tonight. No lockups, but once you press standby, you can't get it back out without power cycling.So I may need to investigate the standby circuit.The very large caps are bulging at the top, but that may just be the plastic cap on top warped, as I can press it flat.I'm still going to replace them and the 680's.I removed and reseated all of the socketed chips, the ocxo, and the GPIB board.

author: lowimpedance
author_rank: Super Contributor
timestamp: February 21, 2018, 05:44:30 am
content: Quote from: Squiddaddy on February 21, 2018, 12:29:43 amIt is but seems to work good enough. Also I had the bulging cap tops too but indeed it was just the plastic covering !.

author: Squiddaddy
author_rank: Regular Contributor
timestamp: February 22, 2018, 02:51:22 pm
content: So after a few days of using the counter, it's been powered up continuously now, the only issue I still seem to have is that it won't come back out of standby. I need to fix that to be able to leave the OCXO powered. It did work when I first got the counter, as I tested all of the buttons, since I knew they were prone to issue.The prints in the service manual are not the clearest, so it may be fun to trace that logic out.I will probably need to replace those caps first, in case there is any noise on the rails.Thanks again for all of the help.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: February 23, 2018, 06:26:51 am
content: I have seen seemingly ok buttons cause this fault, they start to disintegrate inside and hold the button on effectively, which locks up the unit, I would be replacing the buttons first, it only takes 1 of the buttons to fail to cause this.I have done a couple of videos on the replacement on my YT channel, I had links to the buttons I used in the description.

author: Squiddaddy
author_rank: Regular Contributor
timestamp: February 23, 2018, 02:24:09 pm
content: Yes, I used your link to order the buttons. I've had them a while just in case he runs out.They just felt good enough to not need replacing, but I can definitely work on that.Been running now almost 48 hours and no lockups, but I haven't tried standby, just left it on, because I'm testing a GPSDO board and checking calibration.Thanks for those good teardown videos too!

author: sundance
author_rank: Regular Contributor
timestamp: May 08, 2018, 11:07:55 am
content: @Squiddaddy:I recently also got a Racal Dana 1992 counter myself. It also has some problems like missing decimal point in the display, displaying random numbers while nothing connected to either input (all of them left open) and occasional lock ups.Is it "normal" for that counter to display rubbish with open inputs?How's your counter now?Have you replaced the capacitors already? Installed kinda heat sink for IC39?All your lockup problems gone?-sundance

author: Squiddaddy
author_rank: Regular Contributor
timestamp: May 09, 2018, 01:27:57 am
content: I haven't had a chance to work on it since i posted, so it's still in the same state.Yes, i sometimes get rubbish with open inputs. It may be the trigger level being set low, and picking up interference.Or it may be those caps.You should check your display chips and possibly reseat them in the sockets and see if it fixes the decimal.There is an led self test in the manual you can try too.I will post back to this when i get a chance to work on it again.

author: sundance
author_rank: Regular Contributor
timestamp: May 15, 2018, 08:48:07 am
content: Missing DP issue:I ran the diagnostics (flashing all segments and LEDs). Surprisingly only one DP works here; it's the rightmost of the 9 counter digits.All the left 8 digits (being 4 x 2 digit display elements) don't show DPs. On closer inspection it seems that these "double digits" have no LED where the DP is located... Maybe they have been replaced with incorrect modules...Lock-ups:Since the counter is switched on daily no more lock-ups occurred. Maybe the old capacitors are to blame here, too.It doesn't hurt replacing them anyway...