Replacing Broken Power Circuit Of A Philips Dock

[cyberteen]

Hey guys,
I have a philips dock (dc291/37). It runs on 110V,60Hz supply. Ive been using it in India(220v,50Hz). Unfortunately, some of the SMD caps in the power circuit got burnt, rendering the dock useless now without a power supply circuit.

Since, there is no way to replace the burnt caps and resistors, I am thinking of making my own power circuit for this dock.

The board gives out (GND,9v and a 3.5V) output. Hence, All I want to do is to build a simple rectifier circuit which accepts 220V 50hz input , steps it down, rectifies it and regulates and delivers the required dc outputs.

The original circuit seems so complicated, so im skeptical about my attempt to repair this. I am attaching a pic of the original power board, do let me know if my approach is right and can be successful.

Pls excuse me for any silly doubts, ece undergrad here, trying to get hands on! Pls let me know if more details required!

 

[HellasTechn]

The board gives out (GND,9v and a 3.5V) output. Hence, All I want to do is to build a simple rectifier circuit which accepts 220V 50hz input , steps it down, rectifies it and regulates and delivers the required dc outputs.

Is it worth spending so much time and efford to make you own psu ?

One other thing you could possibly do if you can not get a spare original PSU is to try finding an other PSU that can supply the required voltages and connect this with your dock.

in picture 2 upper left corner you can see the voltages at the corresponding pins.

 

[cyberteen]

I've marked the burnt area..

 

[cyberteen]

and yeah.. i have no source to identify the values of those components.. this dock doesnt come with any repair guides.. As you said, either i have to find a similar PSU, or I have to build own on my own..
How tedious is it, do u think to build this from scratch? Not exactly complicated like this circuit, but a basic rectifier, with limited components.. How safe is it?

 

[HellasTechn]

It could be made safe but it will be really hard to find parts like the transformer let alone to calculate it's value and the required switching freq.

I wouldn't bother building a new one. Try to look for a spare on e-bay ? or a different one with same voltage and current capability ?

I dont think that there are repair manuals for theese....

 

[cyberteen]

The dock mentions 7.5W.. how do i find the required current?
Will this smps work?
http://www.ebay.in/itm/DC-12V-2A-24W-Switch-Power-Supply-PCB-Noise-Filter-SMPS-Adapter-Small-Size-/291830827830?hash=item43f2790b36:g:casAAOSwaB5Xmdt0

 

[HellasTechn]

If you are planning to use regulators to make the desired voltages at 7.5 watt then i think it will not be possible.

normal regulators like 7809 can deliver 1 amp maximum only with proper heatsink.

 

[shrtrnd]

I second HellasTechn advice on this. Those power supplies are complicated for a reason.
If you do buy a replacement, don't buy the exact part number for 110VAC that you originally fried, buy one for
the 220VAC you're using.
Trivia on this. I myself fried two of these power supplies while overseas for exactly the same reason (for HP computers). In both cases, the transformer itself also burned open-circuit.

 

[Mongrel Shark]

I don't think thats burned caps on the board. Looks like the regulator got really hot trying to step down all that extra voltage... Which may have cooked a couple of SMD parts. Which suggests the transformer is still good. I see a small transistor and an optocoupler that might have had a bad reaction to too many volts. Everything else on that board looks rated to handle the abuse.

My 2 cents. Why did you run it on 240 in the first place? Sounds like you should have known better.
Guessing you have other 110v stuff you like. Maybe make or invest in a step down? So you can use 110v apliances....

 

[cyberteen]

I second HellasTechn advice on this. Those power supplies are complicated for a reason.
If you do buy a replacement, don't buy the exact part number for 110VAC that you originally fried, buy one for
the 220VAC you're using.

I couldnt find the exact replacement part of the same board.. so i thought any 220VAC smps should do and i could probably use some regulators to provide my required dc voltage

 

[cyberteen]

My 2 cents. Why did you run it on 240 in the first place? Sounds like you should have known better.
Guessing you have other 110v stuff you like. Maybe make or invest in a step down? So you can use 110v apliances....

Lol Yeah! I was using a step down adapter for this device.. but unfortuately some one in my home took it off and ran this dock without it, and it surprisingly ran without any trouble for some days. so no one noticed it until it got fried.

 

[HellasTechn]

and it surprisingly ran without any trouble for some days. so no one noticed it until it got fried.

are you sure that it wasn't a universal type 100-240 V ? input that was burned for some random reason ?

110V device would not last under 220V for a second !

 

[cyberteen]

are you sure that it wasn't a universal type 100-240 V ? input that was burned for some random reason ?

110V device would not last under 220V for a second !

Yeah I know. I might be wrong in the fact that it was running days without the adapter.I personally dont use use the dock much, only my mom uses it in the kitchen. so I dont know where exactly the problem is.. The device clearly reads 120V, 60Hz. Not the universal type. When i found out the device wasnt working anymore, I noticed that it had been plugged in directly without the the step down adapter.

 

[cyberteen]

So guys, what do you think is the solution for this?
Its not possible for me to order a replacement part of the same psu.. its not available..
The closest i can get is some 220VAC smps, which cannot still deliver the required DC outputs.
Something like this: 12V 2A 24W 220VAC input smps
Still, I thought maybe I could use some regulators like 7805/09. But as @HellasTechn says, those normal ones might not be able to withstand those currents, are there any other voltage regulators, I could use?

 

[cyberteen]

anyone pls

 

[73's de Edd]

Sir cyberteen:

( and would you be a 13'ish or 19'ish cyberteen)

Why 'soitanly . . . . .let me just consult my . . . . .

Hmmmmmmm . . . . . . . .Hmmmmmmm . . . . . . .Hmmmmmmm

Ohhhhhhh-tayyyyy . . . . .I'm ready !

After fully evaluating your dee-vices parameters:

PRE- PLANNING:

Would you initially be willing to spring some of your HARD earned allowance "munney" to
buy 6 " D " cells ?
I can still get them at "one Amellican Dollah" apiece, at our Dollar Store's . . .do you have an
"Indian Store" . . . . . or maybe . . . . . the Marrakesh Bazaar ?

That is so that we can initially confirm that the circuitry that is being SEPARATE from the units
currently dee-funct power supply is still operating properly, just as I suspicion that it will be.
The evolving game plan will then be to use individual short jumper wires to solder to sequential
+&- cell connections, to end up with a series acquired 9V battery supply.
(No use in spending an additional fortune for battery holders, for this temporary evaluation
procedure. ).
UNLESS . . . in testing . . . .it is found that the power consumption at a "Mothers" playing
level is so conservative, that battery operation just might be a consideration . . . .for portability.

ANALYTICAL EXAMINATION:
You can see that the power supply output plug provides both a 9VDC for the docks principal
electronics and also in the order of 3.5 VDC for the cell phone " dockee ".

PROCEDURE:
Now initially, will you be able to handle the soldering of those 6 cells together or do you have a
well equipped " electrical / electronics nerd " acquaintance that can do that task for you?
It will require either a soldering station or a heftier iron / gun as those bulky cells end caps and discs
SUCK heat away in a hurry.
You will also need a DMM in order to measure DC voltage AS WELL as inserting it in line with the
created 9VDC battery supply to read current consumption milliamperes/amperes..
That is to CONFIRM just EXACTLY what current supply requirement is needed when the unit is
cranked up at MAX volume.
Also we will later check the same current requirements of the 3.5VDC supply, but I fully expect it
to be but a mere trickle charge level. It will merely be compensating for the on dock used playing
time.

IMPENDING PROCEDURALS:
A logical power supply choice would be a common 12VDC 1 to 2 A linear/transformer based power
supply WALL WART using 220V Indian AC power plug input.. ***
I suspicion our current meterings will prove a 3 terminal linear LM7809 to be adequate for the 9V supply derivation..

Wall Wart Type *** . . . . . it just needs to be incorporating your 3 term Indian AC input plug.

For that 3.5 supply situation, you need to provide me a better photo of both top and bottom HALVES
of the PCB with the 5 pin output connector.
It is too dark to ascertain the manner in which the circuitry / components derived the voltage drop.
Take the pic outdoors . ..straight down . . . .squared in the viewfinder . . .using overhead sky lighting . . . .
with no sun shining on the board to make any shadows . . .in as close as possible to fill in the frame.

The wall warts end lead comes into the unit and connects to the board to gain some additional filtering that is already mounted on the board.
What little construction needed, can be on a small perfboard.

Thassssitttt . . . pending your feedback . . . . . .


73's de Edd

 

[cyberteen]

Hey Edd,
Thank you for taking your time to write a comprehensive answer!
Btw, Im 21.. not a teen anymore!

First of all, regarding the intial testing, let me know if six of this eveready D cell is good enough?
http://www.needsthesupermarket.com/batteries/4454-eveready-leakproof-battery-r20-15-v.html

and regarding soldering these, umm.. well, I do have some experience soldering some ICs and stuff and I have an average soldering iron, not a station with those temp. settings. And ya I Got a DMM.

and here are the pics you asked for analysing the 3.5V circuit..

 

[cyberteen]

Also, just out of curiosity, can we use a 12V,1A SMPS to power the circuit instead of these 6 D cells?

 

[73's de Edd]

Sir cybertwenties:


Also, just out of curiosity, can we use a 12V,1A SMPS to power the circuit instead of these 6 D cells?
Give me more details on your mentioned supply and a pic.


On photo # 2 down, you still get an F in your macro-photography expertise, but I believe that I can work with it when I look DEEP-DEEP down in that black hole.
I was figuring that the wall wart that I showed could be acquired for very little cost as a used unit that someone or some thrift store might have, veeeery-veeeeeery cheeeep !.
On my initial reference to batteries, I was considering we were in the mode of " being stranded on a desert island" with limited parts access available for working with..
Deeeep down in that black hole, on the next picture,I was just barely able to make out a green metal film resistors end poking up..

Check out my markup of your photo number #4 and see if the Rx and Rxx resistors seem to be in that position on your board then take an ohmmeter and measure their values. If their resistance ratio is being ~ 2.5 to 1 . .that is HOW the 3.5VDC supply is being acquired from the principal 9 VDC level..

Needed info below, to now be acquired and passed back for my evaluation:

Give the capacitance and voltage rating on the main cap to see how much overtaxed it was.
Normally one is expecting only 160-170 VDC to be hitting it, when properly used on 120VAC input .

See if the main power transistor beside that main cap is being of the MJE13004-5-6-7- family.

Give A B C D E electrolytic capacitors voltage and capacitance ratings.

The rectifier case above those caps that I marked, seems to NOT be a full wave bridge with its typical 4 terminals, but a 3 terminal dual diode.
Confirm its marked on numbering.
It will eventually be pulled out, to positively isolate the old power supply portion from the add on mod from any bleed thru..

OBSERVATIONS:

Photo 4 markups:
Made in YELLOW

The triad of surface mount resistors from the main power supply were inadequate in the initial voltage drop to the primary of the power transformer. The duo on the power transistors emitter were dissatisfied also.
The foils had a flashover .
Little surface mount IC was also not any too happy.

Mental note:
Revise power transformer marking from TOPOW-1 . . . .to KA-POWWWWWWW !

MARKED UP REVISIONS OF YOUR PHOTOS:

73's de Edd

 

[cyberteen]

Hey Edd,
Here are the details of the components you asked for:
main cap : 22uf 400V
a : 1000uf 16v
b: 470uf 10V
c: 470uf 10v
d: 1000uf 16v
e: 1000uf 16v
f: 200uf 16v
R : 10 ohms(the metal film one)
one beside main cap: svf4n60f 600v n mosfet.
schottky rectifier - srf1045c

and btw, the rx seems to be a cap(the 'c' one) rather than a resistor and rxx is the metal film one(10 ohms)..

Here is the pic of the smps i was talking about..: