Saturday, 31 March 2012

Pansaonic inverter microwave cuts out, stops, resets: 2M236-M42 NN-A713a

This microwave was not heating food, cutting out after about 10 - 20 seconds.

Trying to use it, all would sound normal for a couple of seconds but then there was a buzzing arcing sound and relays would start to click and finally the microwave would stop and the timer reset itself.

There was some information on the web about Panasonic microwaves showing error codes but it was showing nothing after it cut out.

The microwave was opened up and (carefully) run with the cover off to see if the arcing was visible, possibly see something else ? On initial inspection nothing could be seen, just the original symptoms heard.

The microwave lamp comes on with the power and was making it hard to what may have been arcing so that was disconnected.

I still couldn't see anything so decided to power off and just have a look at the magnetron, there was talk on the web of seeing the magnet had cracked, I could measure the filament too.

Well upon removal I was a bit shocked, the side of the magnetron that could not be seen with it in place looked like this....

Hmm, that doesn't look right ! It looks like it got a bit hot !

Inspecting the rear air vent it was totally blocked with grease and fluff. The picture is after I started to clean it.

So a new magnetron was ordered off ebay, only £28 (cheapest local shop wanted £60).

Here it is next to the old one. All the adverts on ebay say the new one is a genuine Panasonic item sourced from Panasonic direct, just not branded because they are used in many brands of microwave for rivals ? No way to be sure.

In it went and all working again. :-)

Friday, 3 February 2012

Philipos DPV630 faulty power supply.

A DVD player that would not power up, just a flickering red standby light.

A close inspection revealed  a bulged capacitor. A chance to use the ESR meter in circuit, it confirmed the capacitor was bad.

Component out, definitely gone.

New capacitor in and it was working again.

Sky + faulty power supply.

A Sky+ box stuck with a red light, would not power up.

The output capacitors were bulged and replaced but still no boot up. The main input capacitor looked visually ok but was checked with an ESR meter, it did not register a capacitance or a resistance ! totally shot.

New one in (circled below) and the machine was working again.

Sunday, 1 January 2012

Philips 190S backlight fault

A faulty Philips 190S, the display would come on for a couple of seconds, then go blanks. Typical of a backlight fault.

The backlight was coming on ok, I have seen bad capacitors cause this fault but following a strip down all looked ok.

All seemed ok using an in circuit ESR meter.

I found the circuit diagram on line and this was useful for the next step of fault finding. The fact the lamps came on indicated most of the inverter circuit was ok. The panel has four lamps powered in pairs. If you unplugged one par the fault did not change at all, screen lit up briefly, if you unplugged the other pair only then the panel did not light up at all, this indicated this bank of lights was faulty.

The data sheet for the lamp driver chip showed that if all lamps do not light it shuts the circuit down. This seemed to be what was happening. There is not much in the backlight circuit after it splits to the two banks of lights. A check of the driver transformer for the half that did not light showed it open circuit, fault found !

The picture shows the faulty transformer removed, the output windings (two pins on their own) were open circuit. (confirmed low ohms on the other working half).

A quick ebay search for the board number showed that transformers were available for ~£5 the pair deliviered (the two are not interchangeable due to physical pinout). However £10 shipped would get you the whole board. It was nice to fault find to the component level but it seemed daft not just to get the whole board.

A month later the board arrived and in it went, all working ok.

Dell E198FP Dead, no power, flashing green led

This monitor would just flash its on button, no display.

A quick strip down, bracket off, four screws out, prize off front bezel, four screws holding the electronics to the panel, then the electronics can be flipped over.

Out with the power board and the fault could be seen, two bulged capacitors

 both measured bad when tested.

New capacitors fitted and all was ok :-)

Monday, 31 October 2011

Philips 190B Fuse blown arcing buzzing faulty.

This monitor had blown the fuse in the mains lead following a sparking sound !

I stripped it down, fairly straightforward. Undo all the screws at the back, the stand screws then two longer self tappers that hold the speaker bezel and screen bezel on. Then its a case of unclipping / prizing the bezels off.

The LCD panel then unclips from the case allowing it to be tilted out. The screws holding the psu / video board cover can be removed.

I powered the board on with the covers off and was greeted with the following !

So it was fairly easy where to look next. !

A poor connection at the PCB on the live wire of the mains input was the cause. The solder hole has a heavy duty insert to prevent this kind of thing but the heat and stress must have just got worse, leading to the arcing when the track finally broke. I suspect the internal inrush limiters meant that I could repeatedly produce the arcing in the video without the fuse blowing again.

It was cleaned up and re soldered with a bridge on the track to beef everything up.

Re assembled and monitor then working fine !

Sunday, 9 October 2011

HP Officejet 6500 E709a Series dead faulty PSU 0957 2271

A HP Officejet 6500 E709a printer had a dead / faulty PSU. Printer would not power on and no light on the power supply.

Opened up, nothing obvious to see. A check of all the discretes showed the diode circled was short. Out of circuit it still measured dead short.

A VSB3200 was the culprit, a 300v 2A Schotcky rectifier.

(picture shows new diode fitted and dead one out)

Tested working ok !