ElectronicNoobBlog

I’v got my old hairclippers made by Philips but they suffering short work time… sometimes i had go over wire.

I decide give them a try to fix.

It turn’s out that model of Philips hairclippers was quite easy to open without damage enclosure after putting everything back.

I feed it by the best (in my opinion) possible of shelf battery NiMh Eneloop.

Here are some pictures of that simple repair:

Hello all Electronic Noob Blog viewers.

Today i was doing calibration of DDM 235 made by Sinclair Multimeter – quite vintage 🙂

I plug it to my bench power supply, witch floating ground (insulated from earth).

I made simple repair and after finishing calibration of DC, Resistance, Current i went to AC voltage.

I decide to quick measure AC voltage in outlet (230V 50Hz) and compare result to my analog meter to decide is it need any adjust.

I’m always take caution while doing witch live voltage and have my own power on method.

First i make sure that device under test is disconnected, i made adjustments, turn power on on device panel, take few steps back and plug device into power strip witch another switch … from few meter i switch power strip, i something smoke i hit switch again… that’s save me many times from breathing smoke from cooking capacitors, hitting via starting motors etc. and today save me from being hit in my face via semiconductor parts… that’s might sound funny but i think no-one want to be hit in the eye…

About DM235 i will write another post… but find why it’s exploded ?

It exploded because electric found way from power outlet -> threw multimeter -> threw power supply back to grid network closing circuit…

I do a quick check  grid “hot wire” -> bulb 100W -> isolated power supply output = full bright light 🙂

Of course that should not happen because my PSU is floating ground… and that’s mean it should be separated from grid threw transformer…. but it is not…

After opening power-supply i found blown “ceramic capacitor” with was connected between GROUND and NEGATIVE post terminal…. blown ceramic capacitor have full short patch… and that’s the way how current pass threw DDM to grid…

After removing blown capacitor my PSU start being floating again 🙂

Take big lesson from me… if your PSU is floating and You want use it as floating… check if there is capacitor across terminals… because when apply AC voltage it will blow and will damage Your device if it need to be isolated…

Historical images of using thermal transfer method.

Working very well. Old pictures, i don’t have any information. I downloaded board from internet.

Another experiment – of course not working

That pictures have few years. I was trying to develop own lead-alum battery for solar purpose. Without success.

Recently i’m working to fix PHILIPS SCE7640/12 Laptop 19V 2000mAh power bank.

I’v got from there 3 2000mAh fully operational Li-Poly batteries :)))) (one of them was bad)

So i’m was looking in my lab, for some use for them… then i notice my USB Power bank… it should have 12000 mAh capacity…. i open and check… Yyea… around 3000mAh  real capacity (3V discharge) divide by four batteries mean 750mAh per cell !!!.

I found that 3 x Li-Poly batteries will fit inside this power bank…

I discharge them, stack in parallel and have 3.7V at 6000mAh capacity (declared when new).

After doing measurement, i got 5560mAh of real capacity 🙂 – Not bad

I added fore safety measure  – NC thermal switch witch i got from other notebook battery.

It was really good job, because i double capacity and lose some weight!

Here are pictures from fixing.

Good job! 🙂

Have You trying to repair device witch blow fuses ?

Recently I was fixing a power supply witch shorted rectifier bridge and then i was using series light bulb trick to let me try find cause of short and prevent blowing fuses in my lab and melting traces on PCB. Then i just solder bulb into fuse holder.

Few days ago i got a computer PSU to fix, and he’s also blowing fuse in my lab, so i decided to use light bulb trick again, but  this time i build more usable device for this and future uses.

So what’s series light bulb trick in few words.

You are putting for example 100W light bulb in series with Your device.

Light bulb will act like resistor and allow to pass only 100W to device (full brightness) and let You actually see how “short” looks,  for example is it solid or blinking when transistors get switched on.

If Your device is working and took for example 50W, (You put 100W bulb in tester) when using light bulb trick You should get 50% of brightness, if  took 25W You should see just glowing etc.

If device is fully shorted always 100% brightness.

You can put different bulbs 20W 40W (etc) to make Your check diagnose more accurate.

For example when You put a switching wall plug PSU to 20W bulb, it should for few seconds glow bright (charging capacitors) then goes dark or amber…. if not  and it’s lighting ( full brightness – that should be a short)  for example 50%…  you possible have shorted output or input filter capacitors and they adding fiction load to Your PSU. Bad output filter capacitors may also be spotted by hot psu without any load.

Here are some pictures from building and seeing “in action”.

Make sure You put PHASE wire by bulb, this will show You light also when You will be shorted to ground not only neutral wire!

Play witch 230V is dangerous, if You don’t know what are you doing! DO NOT FOLLOW this tutorial and stay safe witch low voltage circuits !

I spend few Years witch low voltage circuits before feel confident to start fixing high voltage sections! 

!Notice, PSU show short also when switch is turn to OFF!

I notice that my illuminated  rocker switch in power strip stop working…

It might look stupid, but actually it is really helpful, just one look and i know that power is exiting in outlet.

Unscrewing power strip is impossible due to non usable screws.

I actually found that switch is just pushed (just need pry with flat screwdriver) into case, and leads are long enough to re-solder new one without opening case.

Here are some pictures from “repair” ( to be fancy i ordered from china green one 🙂 )

Success! 🙂

Hello all ElectronicNoobBlog viewers,

Few day’s ago i got a 9V 7A very old (198x) years switching PSU.

It was “thrown away” because it was blowing fuse inside PSU and in power installation – so short was very massive:).

First after opening i spot swollen filter capacitor at 220V side.

I removed that filter cap (both) and replace with new one, then put new fuse in PSU and connect into power…

Bam! blown… fuses in lab goes off.

Fuse was very dark, so it’s mean massive short and lot’s of current passing.

To confirm, i soldered in place of FUSE 120W lamp and try again. Lamp was glow at full brightness with little flickering.

I started from checking rectifier diodes, and found one shorted.

I don’t have same type, so i replace all four  with higher current and voltage.

It was little tight but still looks pretty.

Power again, lamp glow very very little in 1 second (when charging capacitors) and goes off.

After confirming output voltage i remove lamp, put fuse and put everything back for 24H test. – Work perfect!

Here are pictures from repair. You can spot “shorted” diode on meter (i measure working for contrast).