Meterman 33XR multimeter service manual?

[Axtman]

Does anyone happen to have a service manual for a Meterman 33XR (Amprobe 33XR-A) multimeter?

I need to calibrate the meter by adjusting the small pots inside, but don't know what pots do what.

Thanks!

[BILLPOD]

Good Morning Axtman, Which functions are off, and by how much?   What references do you have to compare your readings to? 

[J-R]

Be aware that this is just a basic 3,999 count DMM with 0.7% DC accuracy, so even when working "correctly" it can be pretty far off.  24V could be between 24.18V and 23.82V for example and still be within specifications, and it goes downhill from there with the other functions.

If it's further out than that, then it's probably faulty, rather than needing adjustment.

[Axtman]

I understand that the meter is a pretty basic averaging manual ranging multimeter. I got it "as is" at an electronic recycling store for $35 USD so my expectations were low.

I cleaned it up and found the 0.315A 1000V fuse was blown (but not the 10A fuse). One of the leads to the beeper was cut. So I repaired the lead and installed a temporary fuse.

I ran measurements at different values and compared them to my Fluke 87V. To my surprise the Meterman was pretty close to the Fluke. The Meterman beat the Fluke at high frequency measurements. The Fluke went up to about 400k Hz where the Meterman went to about 4M Hz. The Fluke was faster with readings and continuiity check beep.

One of these days, I still would like to find a service manual for the Meterman.

[J-R]

Picked up my 33XR-A back in 2018 for $36.35 from Amazon Warehouse.  I also bought it because it was a good deal.
Beeper leads were cut most likely because it's very loud?
Fuse might be blown because this DMM uses the mA/uA jack for capacitance measurements, although it's easy to blow a mA fuse when measuring current too.
Continuity function is shared with diode, so it's glacial in my opinion. (Capacitance is slow too, IMHO.)
Also, while it can count higher frequencies, the voltage/current measurement specifications are only rated from 45Hz to 500Hz.

Annoyingly, there are at least a handful of different permutations of this thing floating around.  1MHz, 4MHz and 40MHz frequency ability, Wavetek/Meterman/Amprobe branding, and 33XR or 33XR-A, and various labels for the frequency dial position.  Mine is Amprobe 33XR-A branded, 4MHz but the dial simply says "Hz".

[floobydust]

One can figure out the calibration trimpots from tracing out the PC board. You can post pics if you want to figure it out. I've done this for a few products.

Wavetek/Meterman multimeters were also sold under the Amprobe brand name. Sometimes their OEM is GW Instek.
Try ask them (Amprobe) for the service manual/cal information. I did that and once and it went OK.

[J-R]

Yes, I've received calibration manuals for other Amprobe products when I've asked.  I did ask for the 33XR-A but I think due to the holidays I've not received a response yet, yea or nay.

[J-R]

I realized I never actually tested above 4MHz on my unit.  It does also have the 40MHz range.  The included manual oddly states (sic): "Range: 4 k, 40 k, 400 k, 4 M, 1 MHz"

But it's a bit of a niche feature.  You have to push the voltage up at the higher frequencies for it to detect anything.  So no chance of detecting higher clock signals for example.  I used a coax to BNC adapter, BTW.

[J-R]

Amprobe says no help for this model.

[floobydust]

Then PCB pics and ID'ing the chip used would make it easier to ID the trimpot's function.
Example 4,000 count of this era was like FS9721-LP3 usually with trimpot for the ref voltage, ACV and some DMM's had a Capacitance cal trimpot too.

[Axtman]

Here is the meter. I will open it up and get a gut shot later.

You will notice this is the 40M Hz version.