How To Reverse Engineer a PCB With No Datasheets! Dead Battery Charger Fault Diagnosis & Repair

[@Hellhound604]

Love your fault-finding videos. I normally look at your measurements and see if I can deduce the fault before you do.😂😂😂 I know, you take some long steps just to explain to the viewers the how and the why, but still fun. Please continue with the reverse engineering videos, there are always new things to learn.👍👍👍

[@TheEmbeddedHobbyist]

if they are using old school LED's the green will have a higher forward voltage than the red, say 2V. the red will may be be about 1.5V. so with the fet off the green led lights but turn the fet on and the RED turns on dropping the voltage across the green led to that of the red led, so the green led goes out. simple switching of colours with one signal.

[@warwickbunn1250]

Thanks. That answers my question about the 2 LEDs being connected that way. So the higher resistance green LED gets effectively cancelled by the easier current path when the red one is turned on and the green LED ends up with a positive voltage at both ends or not enough of a voltage drop to operate ?

[@TheEmbeddedHobbyist]

@@warwickbunn1250 it's all to do with the forward voltage of the led's when turned on. with old school led's i.e the ones without the phosphor coating, the forward voltage changes with colour. Red being the lowest voltage, then orange, followed by yellow, then green. so they are a bit like zener diodes then need to reached the forward voltage (think reverse for zener diode) before they conduct and light. So the voltage across the red LED will not increase above it forward voltage unless you burn it out. so put a red and green led in parallel and the green will never light up.

[@Simon-mz7sf]

Thanks Richard. Nice example of turning the physical layout into a schematic

[@surgingcircuits6955]

Would be nice to see a followup after the chip swap, but either way, the reverse engineering was very good. More! Thx.

[@MrMaxeemum]

Reverse engineering is easier when you know the different topologies of switch mode supplies. When familiar with them, recognising them becomes easier in real life. Maybe presenting one of each type would help recognise faults.

[@videolan]

Really enjoy these detective adventures! Many thanks.

[@petopeter4832]

last time I repaired almost the same charger for my brother. I figured out that IC is dead, ordered new from AliExpress and received three of them. Had same markings on it as defected one, but still didnt work at all. Checked them on resistance between pins and readings were not the same at all. I think there are many of chinese versions of ICs even if they are marked the same.

[@klaastroost8734]

Hello Richard, if you install google lens on your phone you can easily translate the chinese datasheet.

[@Jedda73]

That resistor colour code got my attention. After looking at it for a while, I could only figure that it was probably 4.7 ohms with 5% tolerance, and the black band must have meant something else. Was interesting to find out what it was for.

[@Dutch_off_grid_homesteading]

Heya, love these reverse engineering vlog it learned me so much that now I can see how the pcb is layed out without putthing it on paper well till now only with small pcb's but that I guess is a matter of low practical experiance so we are growing nicely thanks so much

[@Manticore1960]

@5:45 you have your probes across the L & N pads, not across the fusable resistor.

[@LearnElectronicsRepair]

Yeah that is a problem with the video edit itself, I also did measure correctly and the resistor is definitely open circuit

[@iamthenotbenamed365]

We like watching you Analyze ...

[@Mcfreddo]

Yes I like it thanks and so to do another would be great thanks.

[@abidsaleem5070]

Nice to see you sir and thanks for the sharing nice information

[@chrishartley1210]

The fusible resistor is 4.7Ω, 5% Yageo FCR range. That last bit of information is from the base colour (grey) and the fifth band (black). The other 4 bands are standard 4-band resistor colour codes. Oh, and it is carbon film.

[@jaxk4912]

At the beginning, when you tested the fusible resistor; you had one probe to the opposite side of the bridge rectifier meaning you were testing across the live and neutral connections. Not the resistor. You may not need to change the fusible resistor.

[@davelowe1977]

Thanks - learned lots again!

[@DumahBrazorf]

I think you probed the fusible resistor wrong Richard.

[@LearnElectronicsRepair]

Yeah that was more an error in the editing as I also did probe it correctly. The fusible resistor is open circuit, which is a good reason why the bulk capacitor does not charge up

[@Roman00744]

I may be mistaken but didn't the chips you ordered have a different pinout than the chip on the board?

[@LearnElectronicsRepair]

I didn't order the chips I showed on the datasheet, I ordered ones with the same part number as the original one. Actually I did get to thinking it may be fun to take a completely different type of 7 pin SMPS chip, as I have some various ones lying around, connect the pins to the correct places FB/Vcc/Isense,D,S (may need to wire some flying leads to do this) and see what happens. 😁 I may also have to play around with the FB resistor values as well is the other IC uses a different internal voltage reference, but knowing the correct output voltage and the resistor values I should be able to calculate the Vref for the original IC. What do you guys think?

[@LearnElectronicsRepair]

Reply to self. That would not be so easy as the feedback network is connected to the output of the AUX winding so I don't know what that voltage is, it will be different from the 5V output voltage

[@warwickbunn1250]

It would be great, as I've wondered how possible a similar chip could be remotely wired up if the original wasn't available. Maybe another video about the intricate details that need to be calculated etc.

[@boblevey]

Excellent!!!

[@mdcd4656]

Hello, Richard you misunderstood the owner, you must transtform the accus to fit in the black charger 😂.

[@everythinginfullspectrum8625]

Hello again, Can't you just measure if there is a short on the hot side from the cord with a multi meter ? positive and zero cont. test ? no need for the bulb thing ? I assume they are connected to a transformer. .. I love your videos! Learnt so much from them! Keep it up!

[@oldguy8177able]

i love this channel someone to explain stuff

[@marcellipovsky8222]

Hi Richard, the S3773C chip is from Siwayengine.

[@MrWatnognietdan]

Love to see more reverse engineering videos

[@adambradley3284]

There's a lot of comment regarding the resistor colour code, but Richard found the answer at 29:27 and did not continue to read on to the 4th band. It states 1st 3 are Resistance Value, 4th band Tolerance and 5th band Black =wire wound. Or am I missing something here?

[@stargazer7644]

That 5V charger is for charging a handheld radio.

[@erikhenriksson455]

That little charger looks like a UV-5R Baofeng Walkie Talkie charger

[@arie1293]

That small charger appears to be for a handheld radio like the Baofeng type or something.

[@grahambambrook313]

More, more!😁

[@Mongoman-oq9bq]

Ya I really like this content .

[@davidrobertson1980]

Rich how come you didn't measure across the fusible resistor before pronouncing it open? You measured across the 240v input @ 5:49 lol

[@sonycrack1]

Last black stripe is for “ Non Inductive “

[@karltest1314]

The Black on the resistor means bifilar wire wound

[@joeds3775]

Black charger is for two way radios...

[@LearnElectronicsRepair]

That makes sense as the customer owns a nightclub

[@melvilib]

I just popped in to say the same. Looks similar to my ICOM one

[@joeds3775]

@@LearnElectronicsRepair yeah, never give security radios or keys...

[@Ralf947]

27:18 The datasheet says in the lower right: "Confidential - Customer use Only" 🤫😅 but if you buy 10 of them... then you are a customer anyway. 😅 I can hardly imagine that such repairs are economical if you have to make a living from them. It's great that you do it anyway, as less waste is always good.

[@LearnElectronicsRepair]

This customer brings me a lot of work, so I am happy to repair things like this for him together with the bigger jobs. I think that is good customer relations and in itself is worth a lot

[@anthonydenn4345]

@@LearnElectronicsRepair The smaller jobs make for some interesting content too. They seem to vary in circuit design much more so than the bigger circuit designs. The bigger stuff seem to err more on standard and safe design.

[@weerobot]

Cool...

[@k3ggaming926]

Hello diode gone wild😂

[@dextervandendowe8329]

I need closure...put in the chip and get it working please😲

[@robinedminson6461]

0.47 Ohm wire wound??

[@Foobar_The_Fat_Penguin]

I'm a bit concerned that it says the charger is for use with lithium ion batteries, which are known to be a bit capricious. There seems to be no logic on the device to prevent overcharging. Unless that part is integrated in the battery itself, it might be fireworks waiting to happen. You may want to investigate, or warn the customer, lest it be your fault because you touched the device last.

[@robinedminson6461]

Correction 4.7 Ohms 5% wire wound

[@jimphillips3992]

Pretty sure that's for a landline phone. 😅

[@freedog632]

That looks like a phone, or walkie talkie radio charger

[@jdean399]

Yes please reverse engineer the other pcb

[@mojosanjojo8528]

Resistor fus is 47 mili ohom

[@paulcohen1555]

I am quite disappointed with the long time it took to decide the value of the resistor and the falure isolation. A fusible resistor will act quite quickly and not generate flames. The spark when fusing will be contained inside. To detect the construction of the resistor, grind the coating with emery cloth or other fine grain abrasive.

[@LearnElectronicsRepair]

To be honest I hadn't seen one of those resistors with this type of color coding before and suspected a lot of viewers were not familiar with it either. I agree I could have skipped a chunk of video where I was deciding the value of the resistor, some of this was retained for 'dramatic effect'. It's sometimes hard to decide how to edit a video as no matter what I do some people will think if was too long, and others will think I should have gone even more into detail. I honestly did consider whether to cut that resistor code part and just go to 'this is value' then decided it was worth leaving in. Same with the short circuit diode/chip. I wanted to present this as a short circuit diode because that is how it appeared, I thought I should 'sell' that diagnosis to the viewer because a lot beginners would have fallen into this trap, then go for the 'ahh but maybe it is something else' twist. I guess I will never please everyone but your comments are welcome. 🙂

[@oliverbockler1094]

Yellow 4, Blue 6, Gold 0.1, Gold +-5%, Black „wire wound Type , 4,6 Ohm