Thursday, 30 October 2014

Panasonic SA PT470 dead, no power.

A Panasonic home theatre system, passed to me as dead no power.

A close listen revealed that the unit was not totally dead, pressing the power button the unit would click on then immediately off (but nothing on the display). This could be repeated a second time but then the unit would not respond. Pulling the power lead would allow this sequence to be repeated.

So the unit was alive and intelligent.

A quick google gave me the manual to download from the excellent site, electrotanya.

http://elektrotanya.com/panasonic_sa-pt470.pdf/download.html

Panasonic / Technics manuals are absolutely superb.

I may do a post about my beautiful Technics SC-CH900 that I finally bought after 22 years ! :-)  anyway..


So I opened it up and stated to take a look. Nothing obvious so decided the best plan of attack was to take the PSU out to get some proper access.

Admission: I took a stonking 360v dc hit from the main cap, Warning,  always approach with caution, measure the high voltage DC caps, and discharge as appropriate.

This fault will leave the main caps charged. I usually check but got sloppy.


So nothing jumped out visually, the mains went through a hefty filter and feeds standby power section of the PSU, the main psu is switched in through a relay, the relay only stays in if the PSU behaves correctly.

I did some passive checking but again nothing jumping out.

A move not without risks but I decided the best way forwards was to bypass the relay and see what wasn't powering up, the brain was obviously not happy and shutting everything down.

Using the drawings I checked all the rails and found the 18v fan power to be absent. I checked the rectifier diode D5805 and found it short. Fitted a repalcement and all good.




Friday, 22 August 2014

BMW E83 X3 PDC fault finding and sensor replacement. 66206989069



The PDC enables as you engage reverse and you are met by a long tone and then no PDC function, indicating there is a fault.

To check the sensors the engine does not have to be running, just but the ignition to second position so the dash lights up and press the PDC button. The long tone will sound. You can now get out to check the sensors.

Put your ear close to each one in turn, you should hear a very faint ticking sound. Any that don't are bad or have a wiring fault. In my experience the sensors do just go faulty, that is ones that look pristine and have clean electrical connectors can just stop working.

Order a replacement sensor. 66206989069 from ebay, £10 delivered

I had a search of the web about removing and refitting the sensors and didn't find a lot of encouragement, some indication of having to remove the bumper.

I can tell you on a model with unpainted bumpers it is possible to replace the rear inner sensors without having to take the bumper off because this is the one I did.

To replace the RHS inner sensor.

Remove the tow hitch cover.

Reach you hand in the gap to the back of the sensor.

Feel for the plug, squeeze and remove the electrical connector, this is in line with the body of the sensor but at the top.

The sensor can now be removed, tricky working blind but quite doable.

The sensor is held into the bumper receptacle with two fingers. Splay the two fingers downward and pull the sensor out. Theses fingers hold onto plastic pips on the sensor holding it in place. The fingers are quite flexible, my tip is to grip the body in the palm of your hand, splay one finger downward and pull on the sensor at the same time, then while still maintaining a pulling force on the sensor (this keeps the pip out of the finger ), splay the other finger. The sensor should then start to pull out from the rear.

Slide the new one in paying attention to the orientation.

My faulty sensor. New one in and all working ok.









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 :-)