Dismantle Repair irecord Pro PMR-200

Presented with a iRecord Pro PMR-200 that had had a 12V plug pack inadvertantly connected in place of the +5V plug pack supplied with the unit.  The owner had detected the smell of smoke and that is of course not a good thing.

The PMR-200 injests analogue video and writes AVI files directly to a USB stick that the user plugs into the side of the unit.

Two screws one under each of the two feet at the back of the unit.

Then gently open & unplug the fan with a pair of tweezers.

Check out the heat sink.  The FPGA that does all the work must get hot.

This is all the parts.  Note the shorter screws hold the PCB and heat sink.  The longer screws hold the two halves of the cover together,

A measurement using the multimeter set to the diode (beep) setting across the input showed about 0.4V drop & a beep both ways round.  This indicated something has gone short circuit.

A sniff of the board confirms a burnt smell.  Visual inspection shows D9 to be discoloured.  D9 is to the left just below the big black thing which is the DC power input connector.

D9 is connected directly across the DC power input and my guess it is a Zener diode with a switch on voltage about 5.5V or so.  If you plug in a supply with more than 5.5V (In this case 12V) then the Zener switches on and shorts out the input.  And so long as it stays shorted then it protects the rest of the circuit.

Connected to a current limited lab power supply.  Set to +5V with current limit on.  Increased current limit and the voltage increased slightly and the current increased a lot.  Switched off.  Touched D9 and it was hot.

Removed D9.

Re connected the +5V.  No current drawn even with the current limit switched off.

Pressed the ON button.  The front panel lights came on.

There may be hope of a full recovery.  But for continued protection, we need to find out what D9 is and buy a replacement.

Turns out it is probably a Vishay SMAJ6.0A Bidirectional TVS (Transient Voltage Supressor).  The Vishay data sheet shows the  SMAJ6.0A Bidirectional TVS has code "WG" printed on it.

I did not have any of these but I did have SMAJ5.0A Uni directional (case code "AE").  So I put one of these in being careful of course with the uni directional one, to get it in the right way round.  The PSU is centre positive and the markings on the PCB are wrong.  But with the bidirectional unit, that is irrelevant.

Powered it up with it's original (+5V) plug pack and the lights come on.

Everybodys happy.