Agilent U1242B repair

[Erik]

Hello everybody,

I've bought an Agilent U1242B about a year ago and a couple of days ago I was doing some measurements and I accidentally dropped my meter from around 7 feet high onto a concrete floor with some thin carpet on it(ouch) . The meter looked allright, no damage to the case at all, not even a scratch and it was actually functioning fine untill I shut the meter off and noticed the buzzer didn't work anymore when I turned the meter on.

I've taken it apart to see if I could find any internal damage but it looked fine at first sight. I've also tested the buzzer but it was ok so it has to be the board itself. As it fell on a concrete floor and after some reading on the forum about Agilent meters and crappy soldering I was thinking of some cracked solder joints and I tried to follow the traces from the buzzer but the board is pretty packed with parts and traces go under parts aswell so it's not easy to do. As I couldn't find any schematic and don't have a spare meter lying around(I bought this one after my previous el cheapo meter pretty much broke down) I think i'm left with a couple of options:

Make high res pictures and try to find a cracked solder joint or just reflow the whole board to be sure it doesn't have any
Hope for the best and send it in for warranty
Send the meter to a repairshop(which will probably be just as expensive as buying a new meter)

Any thoughts/suggestions on this?

Thanks

[VK5RC]

In continuity mode does the display work properly? It may give you a bit of a clue as to how far away the crack is.

[cncjerry]

Check the operators manual and make sure that you didn't turn of the buzzer by mistake. Also, that looks like a crystal in the picture.  Are you thinking it is cracked as well?

[tautech]

In a very quiet room, flex the PCB back and forth, twist etc while listening for a tell-tale click of a cracked solder joint. Hold the PCB close to your ear while flexing.  Don't dismiss a cracked component either.
Good light and magnification may help you find any cracks.
A full detailed study of the PCB might take an hour.
Good luck.

[Erik]

@VK5RC
The display works just as usual, no problems found there.

@cncjerry
I already checked the setup for the buzzer settings but it wasn't switched off  . My first thought was also that the crystal could have a crack but my guess is that the crystal(2.4576mhz) is used for the processor and because the meter itself works just as usual I doubt the crystal is damaged.

@tautech
Thanks for the flexing tip. I will try to do that tomorrow and I will also make some proper macro's of the pcb. If anyone is interested I will post the high res pictures online.

[macboy]

If it is covered under warranty, send it in. They don't fix these, they replace them, so you will likely get a brand new one in return.

[xygor]

I just acquired one of these and the buzzer did not work.  L1 was open.  Its leads were corroded.  Perhaps this is the OP's problem too.   I fished out the wire from the worst of the two terminals, but could not get continuity in order to make a repair or at least measure the inductance.  Does anyone know what the value of L1 is?

[xygor]

I got the beeper to a usable level by temporarily installing a 820-ohm resistor at L1.  I calculate that L1 should be around 68 mH, but I see 47 mH is quoted in general.

[Erik]

Hi Xygor,

Thank you for responding! I didn't expect a solution anymore after a year but you were absolutely correct. My L1 wasn't corroded but I measured it and it was broken. Same as you I installed a 820ohm resistor and it is beeping again! 

Now I only have to order a suitable replacement. I couldn't find the exact component but after taking some measurements I think something like the SLF6028T-470MR59-PF from TDK or perhaps the SRN6045-470M from Bourns would fit although I doubt if there is enough space left solder it. Perhaps a little bit smaller package would make it easier to solder.

Did you leave the resistor in or did you replace it with an inductor? And if you did replace it which inductor did you use?

Thanks again!

[xygor]

Erik,
I am glad this worked for you too and thanks for telling me.  I suspect that this is a common problem.  Mine was working before it was mailed to me, and before it was mine, but the beeper function didn't survive the trip apparently.
Co6aka measured one for me and found approximately 56 mH.  The two parts you cited are both 47 uH.  That's ~1000x too low!

I left the resistor in until I can find a replacement inductor.  I have not found one that small, but there are some at least about the same height.  The original's body is about 0.200" dia. by 0.140 H (5mm x 3.6mm).  I feel no urgency to replace it since it works well enough for now.
Do you recall it being any louder when the inductor worked?  With the resistor, 3746 Hz and 1200 Hz are loudest, the others are not.

[Erik]

Oops, it was indeed the wrong value. Didn't noticed it unill you said so. 47mH-68mH is a lot harder to find in a small package.

But tbh the beeper was never very loud to begin with but it was louder then it is now with the resistor.

After searching for a while I found a 50mH one from Panasonic that will do the job I think:

ELT3KN028C
https://industrial.panasonic.com/cdbs/www-data/pdf/AGI0000/AGI0000CE1.pdf

It's sold in a couple of places like Mouser, Farnell/Element14.

Edit: it's smaller then the original, perhaps even a bit too small.