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Tenma 72-10405 DMM Teardown

Tenma DMM
Tenma DMM

Well it’s time for a new DMM. After the last pair of eBay El-Cheapo Chinese meters just didn’t last very well, I decided a proper meter was required. This one is a Tenma 72-10405, stocked by Farnell for under £60. Not quite as many festures as the cheapo Chinese meters, but I expect this one to be a bit more reliable.

PCB Rear
PCB Rear

Since I can’t have anything without seeing how it’s put together, here’s the inside of the DMM. (Fuse access is only possible by taking the back cover off as well. The 9v PP3 battery has a seperate cover).

PCB Rear Bottom
PCB Rear Bottom

He’s the input section of the meter, with the 10A HRC fuse & current shunt for the high-amps range. The other fuse above is for the mA/µA ranges. The back cover has a wide lip around the edge, that slots into a recess in the front cover, presumably for blast protection if the meter should meet a sticky end. The HRC fuses are a definite improvement over the cheap DMMs, they only have 15mm glass fuses, and no blast protection built into the casing.
There are some MOVs for input protection on the volts/ohms jack, the jacks themselves are nothing more than stampings though.

PCB Rear Top
PCB Rear Top

Not much at the other side of the board, there’s the IR LED for the RS232 interface & the beeper.

PCB Front
PCB Front

Most of the other components are on the other side of the PCB under the LCD display. The range switch is in the centre, while the main chipset is on the left.

DMM Chipset
DMM Chipset

The chipset of this meter is a FS9922-DMM3 from Fortune Semiconductor, this is a dedicated DMM chipset with built in ADCs & microcontroller.

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Cisco 2G Fibre Channel SFP Module

2G Fibre Tranciever
2G Fibre Transceiver

Here is a 2Gbit Fibre Channel transceiver from Cisco Systems in SFP module format.

Shield Removed
Shield Removed

 

 

 

 

 

 

Here the shield has been removed from the bottom of the module (it just clips off). The bottom of the PCB can be seen, with the copper interface on the left & the rubber boots over the photodiode & 850 nm laser on the right.

PCB Bottom
PCB Bottom

Here the PCB has been completely removed from the frame, the fibre ends slide into the rubber tubes on the right.

PCB Top
PCB Top

 

 

 

 

 

Top of the PCB, showing the chipset. There are a pair of adjustment pots under some glue, next to the chipset, presumably for adjusting laser power & receive sensitivity. The laser diode & photodiode are inside the soldered cans on the right hand side of the board, with the optics required to couple the 850nm near-IR light into the fibre.

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Sigma Mini Keychain LCD Photoframe

Front
Front

This is a cheap Sigma branded keychain photoframe. User buttons for power & selecting photos are on the left.
There are two white LEDs on the bottom edge that function as a torch as well.

Display
Display

Front of the unit removed, showing the LCD module. The USB jack is bottom left, next to the pair of white LEDs & above that is the 32kHz watch crystal that the CPU uses for timekeeping.

Back Removed
Back Removed

Here the back has been removed showing the 3.7v Li-Ion cell used to provide power.

Display Folded Back
Display Folded Back

Here the display has been removed from the PCB exposing the chipset.

Chipset
Chipset

Here the CPU blob-top chip & a flash memory IC are visible. The CPU is a Sitronix ST2205U.