HP8116A manual problem

[wiss]

Hi
I'm trying to adjust the frequency of a HP8116A, when I got to the 1 MHz to 9.9 MHz I read this in the manual:

18. Set the HP 8116A frequency to 9.99 MHz.
19. Adjust A1C204 until the measured frequency is 9.99 MHz +-0.5 MHz.
20. Set the HP 8116A frequency to 1.00 MHz.
21. Adjust A1C204 until the measured frequency is 1.00 MHz +-0.05 MHz.
22. Repeat the previous 4 steps until both specifications are achieved.

Step 21 must be a typo! But what trimmer to adjust in that step?
Anyone got a manual without that typo?

[MarkL]

I have an original printed version of the manual and it says the same thing.

If you look on page 9-22 at the adjustment locations, A1C204 is labeled as 1 - 9.99MHz.  So, they may be asking you to find the best position for C204 that satisfies both frequencies (and hope that it's possible).

If you can't get them to converge, I would probably start looking at the "Range Switching" section, see schematic 10.3-9.

My 8116A is due for a cal, and I haven't run through the procedure yet myself.

[wiss]

Thanks!
I figured out that maybe, the accuracy is so low so it's just about getting best fit...
1 MHz is 0.995 to 1.05 MHz and 9.99 is 9.49 to 10.49 MHz...
My instrument is well within spec (and I'm rather unimpressed by the spec...)
But then it is rather stable for a RC-oscillator. I think I did optical pumping of Rubidium with this unit as the RF-generator!

[MarkL]

Well, I finally had a little bit of spare time to do the cal on my 8116A.  The performance check showed the offsets were too high in some cases.

What a pain!  I'm into day 2 and I'm still not done!  Most of the adjustments have too much range and it makes them extremely sensitive, so I don't have a lot of confidence it's going to stay calibrated.

I didn't have a problem finding a compromise for A1C204.

I spent a lot of time on A1R221, A1R224, and A1R130 in the "High Frequency and Flatness (10MHz - 50MHz)" section.  They all interact with eachother and there's a lot of cal conditions to meet.  I found it particularly difficult to get under 43.5MHz when it was set to 42MHz.  I eventually got it, but not by much (step 46).  Did you try this section?

I had a power supply adjustment and the manual says you need to re-cal everything if you adjust any voltages there.  It wasn't off by much, so NEXT time I'm going to re-do the performance check first to see if I threw anything off BEFORE I go diving into a 20-page adjustment procedure.  Sheesh.

[wiss]

No, I only did the frequency part, I will not bother to cal it, will verify settings with oscope instead...

[tautech]

What a pain!  I'm into day 2 and I'm still not done!  Most of the adjustments have too much range and it makes them extremely sensitive,
I had a power supply adjustment and the manual says you need to re-cal everything if you adjust any voltages there.  It wasn't off by much, so NEXT time I'm going to re-do the performance check first to see if I threw anything off BEFORE I go diving into a 20-page adjustment procedure.  Sheesh.

You have to love the "Self Cal" button on a modern DSO.
Exactly why i have no CRT scopes now.

[MarkL]

You have to love the "Self Cal" button on a modern DSO.
Exactly why i have no CRT scopes now.

I have a mix of old and new, but have a renewed appreciation for self cal.

All praise the Self Cal button!

[wiss]

Another thing with the 8116:
There's an accumulator powering the RAM!
My acc had gone really bad and started growing white fungus over the board...
It has been amputated now, but how much current does the RAM take? Can a super-cap to the job? (for, say, a week?)

[MarkL]

The RAM is only used to store the settings when powered off, so you're not losing any cal settings.

The max standby current on the RAM is 1uA @ 25C.  A super-cap has leakage on the order of a magnitude greater, about 10uA for a pretty good 1F one.  So accounting for a couple of Schottky diode drops to build a super-cap circuit, and assuming a 1F super-cap, it should be something around 3 days [(5.0Vsup - 2*0.2Vdiode - 2.0Vterm)*1F / 10uA].  That's not accounting for other leakage through U29C, Q1, diodes, etc., so it's going to be somewhat less time.  More farads could get you more time, but there's also more leakage so you'd have to compare datasheets.

5V super-caps are not cheap.  Why not just replace the battery?  It's a Panasonic BR-2/3 with tabs.  Here's a place that has it for USD$10:

  http://store.batteryspecialists.com/br23atabs.html

There's also a bunch of sellers on ebay for considerably less, if you can believe their date codes.

And if the battery went bad, I would 1) make sure you get ALL the gunk off the board, and 2) check the current draw out of the battery (or temporary supply) when the unit is off.  Maybe there's a reason why the battery died besides old age.

[wiss]

What! It's a lithium?!?! Was way to mushy to read anything from it...
I thought it was some NiCd that was recharged...
Thought CR8 was a zener, but it is CR6 and its a schottky.. ok...
1200 mAh at 1 uA => 1.2 Mh = 50 kday = 137 years, well, that might be enough 

[MarkL]

Yep - it's a lithium.  I'm surprised it was so far gone you couldn't even read it.

[EDIT: See later post.  Some units have nicad and some have lithium.]

Below is a shot of it before I close up the covers on mine.

I'm done the cal and it's better than it's ever been, but I'll never do that again.  There were a lot of adjustments that heavily impact the 2nd harmonic spec (mostly symmetry).  Some of the cal steps don't bother to mention that, and you don't find out until the very end that it's messed up.  The trick is to check it on almost every step and optimize it right then and there.  It's much more sensitive than adjusting the duty cycle or, my favorite, "adjust until it looks linear".

The cal instructions also end before doing anything with A1R413.  They have you set up a carrier and point out what a good and bad offset looks like, and then... nothing.  A1R413 seems to adjust the modulation offset, so that's what I did with it.  There doesn't appear to be any missing pages.

I think I'll weld the covers shut so I'm not tempted to tweak anything.

[wiss]

Here we go!
 

[MarkL]

Yikes!  I've seen leaky batteries before but nothing like that!

You're lucky it doesn't appear to have attacked any exposed traces or pins.

I can make out 13AA-GT1, but that's about it.  Maybe a Nicad or NiMH someone threw in there?

[Seicam]

Hello, long time watcher of the EEVBlog, but first time poster. I just got one of these FG's through ebay yesterday knowing the risk and feeling confident I can handle the repair. Mine has the same battery problem as wiss though it leaked more of an aqua color than white. lol Anyway I removed the old battery and started cleaning up the trouble spots. It was a little GE NiCad (K02A113AA GT1 8211) and I'm planning on getting the replacement Mark suggested. Again it was all very localized, but the chip to the north of the battery in wiss's photo did get a speck or two of aqua on it's pins facing the battery. It's by no means covered and the contacts look intact so I'm hoping it can just brush off and be fine. Does this sound valid or is even a speck of acid fatal in this situation? I can get a good picture of it tomorrow and post it up if it makes evaluating easier.

Thanks,

Cam

[MarkL]

I thought it was strange there are now two cases with the battery as a nicad.  My unit has a lithium battery in it.

I checked the service manual and there is indeed a design change from nicad to lithium.  See change #61 in the backdating section, page B-43.  It says nicad batteries exist in instruments with serial number 2520G06295 and lower (2816A05450 and lower).

*** IF YOU HAVE A NICAD, DON'T SIMPLY REPLACE IT WITH A LITHIUM. ***

There is a circuit that charges the nicad and you don't want to be charging a non-rechargeable lithium cell.

To answer your other question, though, certainly brush off any corrosion but I would also gently wipe the area down with IPA.  If it's being stubborn use a toothbrush but be careful not to dislodge any traces if they appear loose or lifted. 

A "speck" of acid on a couple of nearby pins is not fatal as long as the metal is still intact, but I wouldn't let it sit there.  Clean it all.

[idpromnut]

Hmm, methinks I will be doing some exploratory surgery on my 8116 after all of this battery shenanigans. 

[wiss]

I checked the service manual and there is indeed a design change from nicad to lithium.  See change #61 in the backdating section, page B-43.  It says nicad batteries exist in instruments with serial number 2520G06295 and lower (2816A05450 and lower).

*** IF YOU HAVE A NICAD, DON'T SIMPLY REPLACE IT WITH A LITHIUM. ***

 Ohh, I'll have to check that, still hasn't exploded...

[Seicam]

Thanks Mark I'll get right on that. No I'm a bit concerned about the replacement battery. The last thing I want is for something to explode because the model isn't designed for a lithium battery. Looks like I fall in the category of 2816A05450 and lower since mine's 2124G00687. I looked up the part# in the pdf manual I have and I get (panasonic part #BR-2/3AT2P). When I enter this into a search I get results for basically the same Lithium you suggested before. If I need to get one can you recommend a good NiCad from somewhere?

Thanks again for the quick replies everyone. When you see a thread that's been silent for a while you never know if you'll get a response.

[MarkL]

...
If I need to get one can you recommend a good NiCad from somewhere?
...

The service manual backdating section that I referenced shows the old nicad part number to be HP 1420-0251.  The part description from Agilent's web site is:

  Battery 2.5V .1A-HR Ni-Cd Solder-Tab

It's obsolete and not sold by them anymore.  No surprise there.

There a couple of cross-references I can find:

  Saft America 405313-100
  Energizer K02A113AASD1
  Energizer K02A113AAGT1

Check the specs on the these cross references before buying.  It looks the following site has it for $25, but since you have the original you'll need to compare and make the final determination:

  http://www.energexbatteries.com/search.php?search_query=405313-100&x=8&y=11

[edavid]

Isn't it trivial to disable the charging circuit?

Is there room for a 3xAAA or 3xAA holder?

[MarkL]

You can disable the charging circuit but there a couple of other components, like a blocking diode, that would have to be added.  The service manual has the specific parts and schematic changes between the nicad and lithium versions.

My personal take would be to keep the unit as it was designed and replace the nicad.  It's not worth the amount of time and board hacking to save $25.

[edavid]

You can disable the charging circuit but there a couple of other components, like a blocking diode, that would have to be added.  The service manual has the specific parts and schematic changes between the nicad and lithium versions.

If you add a blocking diode (which can be in the wire that goes to the new battery, so no board hacking), you don't have to disable the charging circuit.

My personal take would be to keep the unit as it was designed and replace the nicad.  It's not worth the amount of time and board hacking to save $25.

I've been having a hard time finding good NiCd packs.  I'm not sure they're really in production any more, and availability is only going to get worse.  So, might as well deal with the problem now.

[Seicam]

I'll have to weigh my options carefully then. I'd lean more towards a NiCad replacement though since that's how this version is designed and I don't want to muck around jerry rigging a special circuit into their high precision setup. If it were something simpler though I'd be right on it. The only thing I'm considering changing is to add some terminals so I no longer have to solder in a new battery should this ever happen again. The unit I've got uses a brass clip to hold the battery in place instead of a zip-tie so it's already held in pretty strong.

Now the good news. I spent several sessions this afternoon cleaning the trouble spots with vinegar and lightly scrubbing with a brush, then finally rinsing it off with  pure alcohol and drying with a blower set to cool. There's no longer any trace of goo on the board. I've gone back to test the continuity from the top of the IC pins where they enter the package to where I can see they connect to elsewhere on the board and they all give a nice clear beep!  Looks like one less thing to worry about. Now I just wait for the battery to get in and can hopefully post a final report that all is well.