Posted on Leave a comment

Panasonic NV-M5 CRT Viewfinder Hack

Viewfinder Circuits
Viewfinder Circuits

 

The old Panasonic NV-M5 has the standard for the time CRT based viewfinder assembly, which will happily take a composite video signal from an external source.

This viewfinder has many more connections than I would have expected, as it has an input for the iris signal, which places a movable marker on the edge of the display. This unit also has a pair of outputs for the vertical & horizontal deflection signals, I imagine for sync, but I’ve never seen these signals as an output on a viewfinder before.

EVF Schematic
EVF Schematic

Luckily I managed to get a service manual for the camera with a full schematic.
This unit takes a 5v input, as opposed to the 8-12v inputs on previous cameras, so watch out for this! There’s also no reverse polarity protection either.

Pins
Pins

Making the iris marker vanish from the screen is easy, just put a solder bridge between pins 15 & 16 of the drive IC. The important pins on the interface connector are as follows:

Pin 3: GND
Pin 4: Video Input
Pin 5: Video GND
Pins 6: +5v Supply

Posted on 12 Comments

Zhiyu ZBP30A1 Electronic Dummy Load

60W DC Electronic Load
60W DC Electronic Load

Here’s a useful tool for testing both power supplies & batteries, a dummy load. This unit is rated up to 60W, at voltages from 1v to 25v, current from 200mA to 9.99A.
This device requires a 12v DC power source separate from the load itself, to power the logic circuitry.

Microcontroller Section
Microcontroller Section

Like many of these modules, the brains of the operation is an STM8 microcontroller. There’s a header to the left with some communication pins, the T pin transmits the voltage when the unit is operating, along with the status via RS232 115200 8N1. This serial signal is only present in DC load mode, the pin is pulled low in battery test mode. The 4 pins underneath the clock crystal are the programming pins for the STM8.

Serial Comms
Serial Comms
Cooling Fan
Cooling Fan

The main heatsink is fan cooled, the speed is PWM controlled via the microcontroller depending on the temperature.

Main MOSFET
Main MOSFET

The main load MOSFET is an IRFP150N from Infineon. This device is rated at 100v 42A, with a max power dissipation of 160W. On the right is a dual diode for reverse polarity protection, this is in series with the MOSFET. On the left is the thermistor for controlling fan speed.

Load Terminals
Load Terminals

The load is usually connected via a rising clamp terminal block. I’ve replaced it with a XT60 connector in this case as all my battery holders are fitted with these. This also removes the contact resistance of more connections for an adaptor cable. The small JST XH2 connector on the left is for remote voltage sensing. This is used for 4-wire measurements.

Function 1 - DC Load
Function 1 – DC Load

Powering the device up while holding the RUN button gets you into the menu to select the operating modes. Function 1 is simple DC load.

Function 2 - Battery Capacity Mode
Function 2 – Battery Capacity Mode

The rotary encoder is used to select the option. Function 2 is battery capacity test mode.

Beeper Mode
Beeper Mode

After the mode is selected, an option appears to either turn the beeper on or off.

Amps Set
Amps Set

When in standby mode, the threshold voltage & the load current can be set. Here the Amps LED is lit, so the load current can be set. The pair of LEDs between the displays shows which digit will be changed. Pressing the encoder button cycles through the options.

Volts Set
Volts Set

With the Volts LED lit, the threshold voltage can be changed.

When in DC load mode (Fun1), the device will place a fixed load onto the power source until it’s manually stopped. The voltage setting in this mode is a low-voltage alarm. The current can be changed while the load is running.

When in battery discharge test mode (Fun2), the voltage set is the cutoff voltage – discharge will stop when this is reached. Like the DC load mode, the current can be changed when the load is running. After the battery has completed discharging, the capacity in Ah & Wh will be displayed on the top 7-segment. These results can be selected between with the encoder.

Below are tables with all the options for the unit, along with the error codes I’ve been able to decipher from the Chinese info available in various places online. (If anyone knows better, do let me know!).

OptionFunction
Fun1Basic DC Load
Fun 2Battery Capacity Test
BeOnBeeper On
BeOfBeeper Off
Error CodeMeaning   
Err1Input Overvoltage
Err2Low Battery Voltage / No Battery Present / Reverse Polarity
Err3Battery ESR Too High / Cannot sustain selected discharge current
Err4General Failure
Err6Power Supply Voltage Too Low / Too High. Minimum 12v 0.5A.
otPOvertemperature Protection
ErtTemperature Sensor Failure / Temperature Too Low
ouPPower Supply Overvoltage Protection
oPPLoad Power Protection
Posted on Leave a comment

ZyXel WAP3205 Repair

Here is a ZyXel WAP3205 WiFi Access Point that has suffered a reverse polarity event, due to an incorrect power supply being used with the unit.

ZyXEL WAP3205
ZyXEL WAP3205

While most electronic gadgets are protected against reverse polarity with a blocking diode, this unit certainly wasn’t. Applying +12v DC the wrong way round resulted in this:

Blown Switchmode IC
Blown Switchmode IC (Fuzzy Focus)

That is the remains of the 3.3v regulator IC, blown to smithereens & it even attempted an arson attack. Luckily this was the only damaged component, & I was able to repair the unit by replacing the switching IC with a standalone regulator. (Replacing the IC would have been preferable, if there was anything left of it to obtain a part number from).

I scraped away the pins of the IC to clear the short on the input supply, removed the switching inductor, & tacked on an adjustable regulator module set to 3.3v. Luckily the voltage of the supply is handily marked on the PCB next to the circuit.

Replacement PSU
Replacement PSU

Replacement SMPS in place on top of the PCB. The output of the supply is connected to one of the pads of L4 (on my unit just an 0 ohm link), the +12v input is connected to the + rail side of C8 & C7 & the final ground connection is hooked in to the back of the barrel jack.

After this replacement, the unit booted straight up as if nothing had happened. All the logic is undamaged!

Makerplate
Makerplate