Author Topic: HP 3478 (Read 8910 times)

xyloeye · « **on:** January 07, 2013, 10:50:48 pm »

I have an HP 3478 that I just changed the battery in and after powering back up, I got a message saying Error 1 (rom calibration). I sort of expected that, but the message flashed and then the display went dead. The power supply is working and I've tried the calibration dip switch on the back. No matter what I do now, no display. Any ideas what might be happening? I was really careful not to short anything, etc. when I soldered the new battery in.

free_electron · « **Reply #1 on:** January 07, 2013, 11:22:20 pm »

ouch ... i hop e you had the machine powered while swapping the battery .... Battery changes must be done with the machine under power, or with a power supply hooked up to the cathode of CR500. or you loose the calibration constants...

to recover :
Turn machine off :
flick calibration switch to ON ,
hold down the blue button + the SGL/TRIG button ,
power up ( with the buttons held down )
short the inputs of the machine (volts to black terminal )
push SGL/TRIG you should get a reading
push Blue button and then LOCAL
press SGL/TRIG ONCE !!!!
display will say calibrating

apply 3 volts to input (remove short and inject 3 volts DC )
press Blue LOCAL
press SGL/TRIG ONCE !
it will say calibrating and then calibration finished ( takes 5 to 6 seconds )

flick the cal enable switch back to protected.

your machine should now work. it will be off on all ranges until you do a full calibration.

xyloeye · « **Reply #2 on:** January 08, 2013, 12:31:56 am »

Oops... It wasn't powered. I did know to keep the 3 volts paralleled on the battery terminals while I changed it. Thanks so much for your quick reply. I'm kind of freaked out about it as I use it all the time. I can recalibrate as I have an EDC voltage/current calibrator. I'll try what you told asap and post the results.

free_electron · « **Reply #3 on:** January 08, 2013, 04:54:07 am »

on some machines it is critical. especially the generators like the 8904.. loose the sram contents and you may loose half the functionality of the machine as it holds the unlock keys ... if you don;t have the unlock code stickers insde the case ... kiss it goodbye.

other machines are non critical. the 8116 will reinitialize. so will a 34970a. others are recoverable like the 3478. just a matter of reinitilizing the ram to default. to trick there is to flick the calibration switch. the 3478 stores a checksum in the ram. if it doesn't match the cpu will attempt re-init but to get write access to the ram it needs the cal switch to be in the right position. the shift/trig button on powerup forces a ram init.

nothing to be spooked about. normal behavior for these machines.

xyloeye · « **Reply #4 on:** January 08, 2013, 06:06:13 am »

Well, I just got done with the procedure. I tried three times and still nothing on the lcd. I think she may be a goner. I wish I could understand what happened. I've blown plenty of stuff up being careless (stupid), but I don't think I did anything to deserve this. Thanks again for your help. Could static have killed the display or its driver?

saturation · « **Reply #5 on:** January 08, 2013, 03:53:40 pm »

Sorry to read. I avoid owning devices from the era that use battery backed up RAM for mission critical data; if you lose it, you could lose the device completely. Getting replacement firmware could be unobtanium or even if the cal constants can be restored to factory defaults to get the meter working, getting it properly recal'd could cost more than the device is worth.

mianchen · « **Reply #6 on:** January 08, 2013, 10:29:19 pm »

I've got one of these meters, at what point should I replace the battery? Will it alert you before the battery dies?

alm · « **Reply #7 on:** January 08, 2013, 10:43:32 pm »

Nope. The discharge curve of a lithium primary cell is also very flat, so the voltage will stay almost constant until it dies. The batteries will usually have an expiration date on them, which I believe is about 10 years after manufacturing. Preventive replacement every ten years is the safest solution, although batteries usually last substantially longer than that.

free_electron · « **Reply #8 on:** January 08, 2013, 11:01:41 pm »

ok , try this :

Power off you r machine.
Desolder the battery - terminal ( the battery has 2+ terminals and one 1 - terminal i believe. if not : desolder the other one.
install a simple switch in that line ( could be a simply jumper : 2 pins where you can plug in a jumper )

leave the machine off with battery disconnecte overnight.
in th emorning :
turn the calibrate switch to calibrate ,
power up the machine holding the blue key only.

see what happens.
attmept to do a calibration for the 3 volts.
when done : DO NOT POWER OFF !!! install the jumper or close the switch first , then turn the calibrate switch to OFF .

probably what is ging on is that the ram is so corrupted the firmware can't recover. letting the machine sit for a few hours powerless should completely erase the ram.

if the ram is a 6116 : when the machine is oof and you are waiting for discharge ; short pin 24 to pin 12 of the chip... if the ram is a 62256 short pin 28 to pin 14 ( if its a 24 pin ram you need pin 24 and pin 12 , if its a 28 pin ram you need pin 28 and 14... that will sort any caps that are there t ohold the ram alive. most likely the ram is a 43256 or smoe other low power variation. those things can survive on as low as 1.8 volts ...

xyloeye · « **Reply #9 on:** January 09, 2013, 12:18:43 am »

OK, I'll let it sit tonight and try that. Thanks again. BTW, how can you know that much about these? There are a few parts in there I don't even recognize!

SeanB · « **Reply #10 on:** January 09, 2013, 05:42:42 am »

He has worked with a lot of them.......

poodyp · « **Reply #11 on:** January 09, 2013, 07:00:33 am »

So I thought my meters were good, but I didn't realize the discharge curves were so cliff-like for these batteries.

free_electron · « **Reply #12 on:** January 09, 2013, 07:18:16 am »

Having access to a real lab kitted out with all kinds of equipment has its advantages... A typical benchsetup in my lab can have 20 pr 30 machines on it. A collegua of mine does nothing but characterise switching regulators. He got two scopes, a dynamic signal analyzer , programmable multichannel load, multichannel sourcemeter, at least six 34401 , four power supplies , a bunch a special current probes and amplifiers. A noise generator , a power amplifier and some other esoteric stuff. And its all powered up and connected when 'torturing' a design. Input voltage, input current, output voltage, output current switch current, inductor current, boostpump voltage and many other things are all monitors simultaneously and plotted on a pc screen. The whole thing is gpib controlled. He can program stepped loads and study the regulation behavior of the loop. He'll make really dynamic loads using the noise generator and power amp. He can do slow variations of input voltage to check if the brownout works correctly and if the regulator starts under strange conditions... Like a very slow starting input voltage. Many switchers have problems with that. Meanwhile the part sits in a climate chamber or it can be shoved under a microscope with lasercutter and micromanipulators so we can probe the silicon... And thats just for a switching regulator... You need machinery if you really want to test a design. Being able to watch all parameters simultaneously is the way to go. Prodding around with only a single voltmeter gets you nowhere..

Another advantage of having such a large machinepark is that you don't send stuff out for calibration... You let the calibrators come to you.... We used Voscal service from hp agilent for years. Big truck arrives, unloads some large 19 inch racks in flight cases that get powered up over the weekend and left alone for 48 hours. Then the agilent technicians come in and start doing the calibration. They stay on site for two to three weeks to do all labs in the building. As i had most room i always made sure to volunteer to host them. That way i could talk to these guys.if they found an out of spec machine they attempted adjustment or even repair. Talking to these guys teaches you a lot about machines and their common problems. Most of those guys are electronics freaks as well. Take em out to lunch and the floodgates open wide. It's a matter of keeping you ears and eyes open. Casually walking by when they have a machine open can teach you a lot. Combine that with access to schematics and using any spare moment to study them and you are set....
Agilent used to have so called bench briefs and a monthly magazine. There is a site on the internet that has all of them. Many articles explained techniques used in their new instruments. Go read all of em. You will be amazed at the kind of stuff you can learn...

SeanB · « **Reply #13 on:** January 09, 2013, 12:20:40 pm »

Thanks Vincent, now I have a month of PDF's to read.

saturation · « **Reply #14 on:** January 09, 2013, 05:04:10 pm »

You couldn't have a better guide to EE and gear than freee-

http://circuitcellar.com/featured/a-prolific-engineers-two-bench-workspace-in-silicon-valley/

Quote from: xyloeye on January 09, 2013, 12:18:43 am

OK, I'll let it sit tonight and try that. Thanks again. BTW, how can you know that much about these? There are a few parts in there I don't even recognize!

xyloeye · « **Reply #15 on:** January 09, 2013, 05:06:41 pm »

Wow. My "lab" is significantly less well equipped. Of course, even with all that equipment, you have to be smart enough to understand what you're looking at, which seems to be the limiting factor in my case. Anyway, I did try what you suggested about disconnecting the battery and leaving it overnight. I got the same result - nothing on the display. There is voltage on the board. Power supply is working, etc., but still nothing overall.

I really appreciate the time you've taken to help. If nothing else, I've learned a lot. I'll keep plugging along on it but I hate for you to spend more of your time chasing this thing from afar.

Thanks again,

Ken
Anacortes, WA

xyloeye · « **Reply #16 on:** January 20, 2013, 04:57:08 am »

Solved! After measuring all the supply voltages and realizing that one side of the power supply was very low, I started looking around with my magnifiers. Long story short, a tiny piece of solder (from the battery change) was shorting two pins of one of the regulators. I couldn't see it the first ten times I looked because it was hidden under the heat sink.

Anyway, thanks for all the help and suggestions everyone took the time to make. All I have to do is calibrate it now.

Ken

saturation · « **Reply #17 on:** January 20, 2013, 01:02:47 pm »

I'm happy for you, persistence pays, I know the feeling very well!

ivan747 · « **Reply #18 on:** January 20, 2013, 01:35:30 pm »

That was a very hard to solve problem wasnt it? Next time use solderwick!

mountaindude · « **Reply #19 on:** January 05, 2014, 11:29:42 pm »

Not sure anyone will notice this old thread, worth a try though..

Could I just place 2x1.5V AA batteries + a diode in parallel with the existing battery (with mains power OFF), remove the old battery, solder in the new battery, remove the temp 2xAA battery?
That would keep the RAM powered at all times, or?

free_electron · « **Reply #20 on:** January 05, 2014, 11:36:04 pm »

yep , that will work.
i beielve there is actually a testpoint to clip on an external battery.

Dave · « **Reply #21 on:** January 06, 2014, 02:03:21 am »

Quote from: mountaindude on January 05, 2014, 11:29:42 pm

Not sure anyone will notice this old thread, worth a try though..

Could I just place 2x1.5V AA batteries + a diode in parallel with the existing battery (with mains power OFF), remove the old battery, solder in the new battery, remove the temp 2xAA battery?
That would keep the RAM powered at all times, or?

Yes, I replaced two batteries just like that. Just don't be a moron like me and forget to put the battery into the holder after you solder your circuit onto the PCB.


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Author Topic: HP 3478 (Read 8910 times)

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