Author Topic: Inside a GWInstek GDM-8251A bench multimeter (Read 13011 times)

BloodyCactus · « **on:** December 06, 2014, 07:32:35 pm »

Got a GW Instek GDM-8251A bench meter for a bargin of < $100, brand new. 12000 count, VF display.

couple of the pics looked good on camera didnt show so good afterward, the markings on the custom chip are

GWINSTEK
DM-82XX-01

Vgkid · « **Reply #1 on:** December 06, 2014, 08:04:17 pm »

That doesn't look bad internally. I wonder what is under the can?

MartyD · « **Reply #2 on:** December 06, 2014, 08:34:22 pm »

Congrats! For <$100 definitely a no-brainer.

Macbeth · « **Reply #3 on:** December 06, 2014, 09:11:24 pm »

Looks great! Brand new for about GBP £60? Blimey, I bet you had to control yourself from biting the sellers arm off and using your best poker face haggling techniques!

saturation · « **Reply #4 on:** December 06, 2014, 10:41:40 pm »

Great catch even if damaged repairing it is still cheaper than new. GW is older and more reputable than Rigol. Was this an Ebay find? That model is still in the active GW catalog.

Ernest G · « **Reply #5 on:** April 05, 2016, 02:22:31 am »

Hello everyone i'm new not only to EEVblog, but to the electronics engineering field as well. I'm on my 3rd semester in collage.
but digress. I'm trying to fix a GDM-8251a from GW Instek. On the main board between the three relays and the face plate there is a resister. Its rather large, A fellow student fried it to a point that it is unrecognizable. if anyone could id this component i would be very thankful. I have tried to find the service schematics for it but i have been unsuccessful. My professor turned it into a repair project. the first person to fix it gets extra credit. thank you in advance if anyone can help me. the location on board is R302. and here is a picture i took.

crispy_tofu · « **Reply #6 on:** April 05, 2016, 03:09:28 am »

It looks like some kind of input protection, maybe a fusible resistor?

BloodyCactus · « **Reply #7 on:** April 05, 2016, 06:11:04 pm »

i can open mine up and see if i can take a pic for you.

BloodyCactus · « **Reply #8 on:** April 06, 2016, 05:32:18 pm »

well it wont help, mine has one of those lasered precision resistors and not a through hole resistor like yours... you can see it in my photos from the first post.

wraper · « **Reply #9 on:** April 06, 2016, 05:36:12 pm »

Quote from: BloodyCactus on April 06, 2016, 05:32:18 pm

well it wont help, mine has one of those lasered precision resistors and not a through hole resistor like yours... you can see it in my photos from the first post.

So what? Its still a resistor of the same value in the same place, just different type.

Macbeth · « **Reply #10 on:** April 07, 2016, 01:11:20 am »

Quote from: wraper on April 06, 2016, 05:36:12 pm

Quote from: BloodyCactus on April 06, 2016, 05:32:18 pm
well it wont help, mine has one of those lasered precision resistors and not a through hole resistor like yours... you can see it in my photos from the first post.
So what? Its still a resistor of the same value in the same place, just different type.

Indeed. It appears the PCB has provision for either in the same space. I guess it's just what type is cheaper that day?

Kleinstein · « **Reply #11 on:** April 07, 2016, 06:00:33 pm »

Having the option for two form factors is not that unusual: it could be to have the option to choose a different manufacturer / type for lower price, better performance or just availability in the future.
So this might indicate the resistor is not a just normal one. So it could be a PTC ar fusible resistor.

The input section is usually not that complicated - so reverse engineering might be an option. It's also a good hint from what ranges are not working and how is got burned. The fun part comes when more parts are damaged.

Ernest G · « **Reply #12 on:** May 02, 2016, 07:49:21 pm »

hello everyone i have fixed the problem since my last post . it was a 2w 5 ohm resister.
and i do thank everyone for there help.

Ernie

vladsol · « **Reply #13 on:** May 12, 2019, 01:42:12 pm »

I'm trying to repair a GDM-8255A that i purchased on e-bay. Found that someone was already tried to repair this multimeter.
I need help with identifying some of missing, de-soldered by previous owner, burned, components. Will be grateful for the help.

Missing parts:
R301A, R301B (under the current shunt R301).

U309 (i guess, there was ADG411BR), R319, Q305, Q304

vladsol · « **Reply #14 on:** May 13, 2019, 04:12:51 am »

Found on the photos above:

R301A, R302A = 0 Ohm fusible resistors.
R319 = 22R1
U309 = ADG411BR

Q305, Q304 = PSOT05C dual TVS diode?

innkeeper · « **Reply #15 on:** May 13, 2019, 05:44:31 am »

I've got the same meter, I love it.

what firmware version does it have?

vladsol · « **Reply #16 on:** May 14, 2019, 08:30:07 am »

The latest FW ver for 8251 and 8253 is 2.30

Thomas · « **Reply #17 on:** May 14, 2019, 08:56:49 am »

But what does the OUTPUT ON/OFF button do?

vladsol · « **Reply #18 on:** May 14, 2019, 09:11:19 am »

Quote from: Thomas on May 14, 2019, 08:56:49 am

But what does the OUTPUT ON/OFF button do?

Just on/off the VFD

JXL · « **Reply #19 on:** May 14, 2019, 07:08:41 pm »

FYI, the firmware detects the part number as ADuC845 V2.1.7

vladsol · « **Reply #20 on:** May 14, 2019, 07:34:24 pm »

Quote from: vladsol on May 12, 2019, 01:42:12 pm

I'm trying to repair a GDM-8255A that i purchased on e-bay.

Unfortunately, several outputs of (bigger) Lattice CPLD, that driving ADG411 switches, was burned

The update file contains no CPLD firmware\bitstream, so... No luck, DMM is unrepairable.

vladsol · « **Reply #21 on:** May 20, 2019, 11:32:59 am »

Can someone check the voltages on pins 1,8, 9, 16 of IC's U304, U309, U303? When DCV range 100mV or 1V selected.


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Author Topic: Inside a GWInstek GDM-8251A bench multimeter (Read 13011 times)

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