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Lafayette DMB-SMD tweezer-type component meter - Rewiew and Teardown

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ciccio:
Some time ago somebody (me) mixed SMD capacitors (the common unmarked multilayer ceramics) and a set of prototype boards was not working. I had to check the components value.
Time to buy a tweezers-type component tester, but  budget was low, and the Smart Tweezers  were out-of-reach.
I got this Lafayette DMB-SMB from one of my local distributors, at the very low  price of 24 euros + VAT (list price is 34.13 euros + VAT)
http://www.marcucci.it/english/prodotti/schede/scheda.asp?ID=13876

Actually the Lafayette brand (once a famous USA brand, specializing in C.B. radios)  is used by it's former Italian distributor Marcucci  for a lot of products, mostly OEM from China.

The same instrument is sold with the METRIX brand (model TCX-01 that was offered to me at 51 euros + VAT) http://www.chauvin-arnoux.com/Produit/Famille_detail.asp?idFam=2112&idPole=1

and I believe is the same that EXTECH sells as model  RC 100 (not the RC 200 that nearly killed Dave on EEVblog episode 94) http://www.extech.com/instruments/product.asp?catid=56&prodid=350


 the  AXIO model 103  and others you can find on the Net.
The instrument is boxed in a nice cardboard box, with Italian and English descriptions. and is supplied with an 3-page manual written only in Italian.
It can measure:
- resistance (auto-ranging from 400 ohm to 40 Mohm)  with 0.1 ohm resolution on the lower range,  and an accuracy of  1.2% plus-minus 3 digits)
- capacitance (auto-ranging from 4 nF to 200 uF) with 1 pF resolution on the lower range, and an accuracy of  3 % plus –minus 5 digits)
-diode voltage drop

Power comes from two 1.5 V button cells , type AG13.

Two buttons :
- FUNCtion to switch on/off and to change measurement function.
-RELative  to change from absolute measurement mode to relative mode.
This function is totally un-documented, but  I found that, by pressing the button when measuring a component, you shift the measurement zero by the actual value, setting the display to zero and subtracting the previous reading from the following readings.
That means: measure a 8k2 resistor, the display reads 08.20 kohm, pushing  REL the display reads 00.00 koms, measure a 15k0 resistor, the display reads 06.80 koms (15.0 – 8.2). I don't see any utility in this, but it does not harm :)

The display is good quality, very readable. Character height is 13 mm.

I've tested the meter with various components,  both soldered on the board and  free on the bench top.
The auto-ranging speed is about 3 to 4 seconds for a  stable reading, except for big capacitors, requiring a very long time for a stable measured value.
Measurements seemed accurate (I've not checked the accuracy).
Resistors were measured accurately and with the above speed both when naked and when soldered on the board.
Capacitors where measured accurately only when naked: capacitors on the board were difficult to measure, sometimes it was not possible to get a "credible" reading.
I must admit that I did not investigate too much… this was the first dislike.
The output voltage when measuring diodes is about 1.6 volts, insufficient for testing LEDs.
This was the second dislike.
The third dislike was the bigger one: the tweezers are too "rigid" and require too much effort for a reliable contact.
The tips are too large,  a reliable contact with the component's pins is difficult to achieve.
When testing naked components, placed on the bench surface, many times the component was lost in the lab, "flying away" because of the bad tweezers tips (see photo at the end of the post) that launched it in the air.

The lack of a reliable contact made the actual use of the instrument  very difficult, and very soon it went back into the box….
It's a pity, because the electronics are reasonably well made, and they work "not so badly",  so when I'll find the time and some suitable material, I'll try to modify the tweezers into something similar to the "Smart Tweezers"design.

Taking apart the instrument is easy: remove the battery cover and the batteries, undo 4 self tapping screws,  remove the back cover and you have access to the rear side of the circuit board.  Notice: there are no input protections (or I did not find any).
The manual and the rear panel  text  clearly advise that the maximum input voltage is 50 V dc.

With some easy effort the PCB is released from the 4 latches that keep it in place, and the other side of the board is accessible.  The display is connected to the PCB with "zebra strips". I did not remove it because, looking from the sides, I've seen that the only component under the display is the meter IC, but it’s a COB (chip on board), and  there nothing of interesting in a "black blob"..

Summing things up: this meter is cheap (at 24 euro),  the electronics are not-so-badly designed (but they should be improved), the mechanics are so lousy that actual use of the meter is really difficult. Thumbs down.

Bored@Work:
Yes, this tweezer is quite making the rounds. I think the ODM is Shanghai Yihua V&A Instruments Co. Ltd. and [edit] it is originally called VA503 http://www.mastech.com.cn/html/en/products-va503.htm and a later version VA505 http://www.mastech.com.cn/html/en/products-va505.htm  Note how they use Mastech name in their domain name, although I don't think they are related to Mastech (aka Precision Mastech http://www.p-mastech.com/).

ciccio:
I think you are right.
The PCB (see board1.jpg) is clearly marked VA 503.

Fraser:
I own one of these 'Tweezer Meters' as well and it's been pretty useful. I agree regarding the backpressure when squeezing the tweezers closed on a device but I will forgive it that fault as it's not a main line tool for me.

I also purchased some Tweezer Probes for my meter for GBP2 delivered to UK from China  :). They work well and I have used them on my LCR meter to good effect. Searching ebay for "meter tweezer" brings up many adverts for them at varying costs.

Mechatrommer:
thanx for posting those pictures ciccio

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