06-04-2016, 11:29 PM
First step - remove battery cover/tilting bail, and then the holster (easier said than done!):
Inside, a single PCB. Quite reasonable at a glance:
Undo 4 screws to remove the PCB:
A closer look at the top and the bottom of the PCB:
So we have ceramic fuses - albeit rated to 250V. The meter is supposed to be CAT II 600V, but that rating only applies to the voltage input - the current connections are labelled as "250V max" on the front.
No isolation slots routed in the PCB, no shields between the naff terminals - what one expects at this price point. The mode switch is also as expected - no gold plating at this end of the market! There are the usual ball bearings and springs to provide the detents. Note the covering of silicon grease around the switch contacts.
An even closer look at the PCB:
Looking at the input circuitry, we can see that a spark gap is missing, despite being mentioned at least twice in the manual. There is a pair of PTC thermistors for protection (not sure how useful they'd be, given the size of them and how long they'd take to warm up). At first glance, the spacing on the PCB looks reasonable, but there is a massive howler on there - look for R1A and R1B. These MELF resistors are 5M each, and are in series to give 10M - and the other end of this goes straight into the IC. The lower ends (green bands) are only separated by about 2mm, so if a spark jumps this, the energy will blow up the IC. Fail.
Moving to the right, we can clearly see the current shunts (R49, R48, etc). Note that VR4 calibrates the 10A range.
Moving up, look at the 2 SO-8 packages. These are doing the frequency measurements. There is a TL062 dual op-amp and a 7555 timer! The circuit is a F to V converter, calibrated by VR3. Explains why the frequency measurements are so poor...
Looking at the top half of the PCB:
Top-left we have a bunch of unpopulated components. I'd bet that most of these are for the contactless voltage detection.
The main IC is an FS9952 in COB form:
FS9952 Datasheet.pdf (Size: 453.34 KB / Downloads: 11)
The crystal is 4MHz. Not sure what U2 is, but guessing it's a voltage regulator - the chip runs on 3V. The MELF resistors (R2-5) are range-switching, working with the 10M seen earlier. Note the poor hand soldering on the tact switches and wires. Note also the flux residue. I did scrape some of it away around the +Ve input socket.
From a look at the PCB and the datasheet, it appears that VR1 adjusts the voltage reference in the IC and VR2 adjusts the AC calibration. D1 is part of the rectifier, which makes use of 2 op-amps inside the IC.
So, not as bad as feared based on previous experiences at this end of the market, though I reserve the right to change my mind once I've used it for a bit! I'm not sure I'd use it on the mains - and definitely not in my consumer unit - and I'd also be cautious with HT, given the problem with R1A/B.
It'll be really interesting to get hold of one of those RS meters - unfortunately out of stock until July now. Apart from the different LCD panel and the different positions of the range switch, these look to be almost identical - I bet it uses the same IC and basic design. I note the RS version has a range button, and temperature rather than the pointless frequency option. Incidentally, if you can find it, the ADM02 also has temperature rather than frequency.
Hope this is of interest,
Mark
Inside, a single PCB. Quite reasonable at a glance:
Undo 4 screws to remove the PCB:
A closer look at the top and the bottom of the PCB:
So we have ceramic fuses - albeit rated to 250V. The meter is supposed to be CAT II 600V, but that rating only applies to the voltage input - the current connections are labelled as "250V max" on the front.
No isolation slots routed in the PCB, no shields between the naff terminals - what one expects at this price point. The mode switch is also as expected - no gold plating at this end of the market! There are the usual ball bearings and springs to provide the detents. Note the covering of silicon grease around the switch contacts.
An even closer look at the PCB:
Looking at the input circuitry, we can see that a spark gap is missing, despite being mentioned at least twice in the manual. There is a pair of PTC thermistors for protection (not sure how useful they'd be, given the size of them and how long they'd take to warm up). At first glance, the spacing on the PCB looks reasonable, but there is a massive howler on there - look for R1A and R1B. These MELF resistors are 5M each, and are in series to give 10M - and the other end of this goes straight into the IC. The lower ends (green bands) are only separated by about 2mm, so if a spark jumps this, the energy will blow up the IC. Fail.
Moving to the right, we can clearly see the current shunts (R49, R48, etc). Note that VR4 calibrates the 10A range.
Moving up, look at the 2 SO-8 packages. These are doing the frequency measurements. There is a TL062 dual op-amp and a 7555 timer! The circuit is a F to V converter, calibrated by VR3. Explains why the frequency measurements are so poor...
Looking at the top half of the PCB:
Top-left we have a bunch of unpopulated components. I'd bet that most of these are for the contactless voltage detection.
The main IC is an FS9952 in COB form:
FS9952 Datasheet.pdf (Size: 453.34 KB / Downloads: 11)
The crystal is 4MHz. Not sure what U2 is, but guessing it's a voltage regulator - the chip runs on 3V. The MELF resistors (R2-5) are range-switching, working with the 10M seen earlier. Note the poor hand soldering on the tact switches and wires. Note also the flux residue. I did scrape some of it away around the +Ve input socket.
From a look at the PCB and the datasheet, it appears that VR1 adjusts the voltage reference in the IC and VR2 adjusts the AC calibration. D1 is part of the rectifier, which makes use of 2 op-amps inside the IC.
So, not as bad as feared based on previous experiences at this end of the market, though I reserve the right to change my mind once I've used it for a bit! I'm not sure I'd use it on the mains - and definitely not in my consumer unit - and I'd also be cautious with HT, given the problem with R1A/B.
It'll be really interesting to get hold of one of those RS meters - unfortunately out of stock until July now. Apart from the different LCD panel and the different positions of the range switch, these look to be almost identical - I bet it uses the same IC and basic design. I note the RS version has a range button, and temperature rather than the pointless frequency option. Incidentally, if you can find it, the ADM02 also has temperature rather than frequency.
Hope this is of interest,
Mark
