Can I replace a burned capacitor?

[stevenkelby]

Hi everyone,

I sold this Esky Tx and Rx on eBay.

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=6025117152&rd=1&sspagename=STRK%3AMESO%3AIT&rd=1

The buyer said it worked fine for a while but then he did something and now the Rx doesn't work so he sent it back and I said I would try to fix it.

Looks like a capacitor has melted (thanks Pat) Does anyone know where to get a one to suit?

If I get one I can probably solder it in myself, I've never done work on a PCB before but I know what to do and am good with an iron.

Thanks,

Steve.

[pmackenzie]

That is a capacitor. It looks to me like the rcvr battery was connected backwards, or too much voltage was applied.
The device above it in the second image that has three legs and a tab is a voltage regulator. It might be fried as well.
The first thing to do would be to change the cap.
You might be able to find a suitable replacement on an old computer part ( hard drive, I/O card, etc)
I think it is a 22uF, 10 volts.
226 = 22 x 10^6 pF = 22 uF
The letter "A" before 226 designates the voltage.


Hope that helps
Pat MacKenzie

[pmackenzie]

I should have also mentioned that polarity is important.
Make sure the replacement has the "bar" or line facing the same direction when installed.
Pat MacKenzie

[stevenkelby]

Thanks Pat, that helps a lot.

Transistor/Capacitor, theyre both the same right?

Joking. Don't know if I'll find one, don't have any old circuitry but I know what to look for now.

Thanks,

Steve.

[stevenkelby]

Thanks for the help, I think it's pretty obvious I wouldn't have figured that out myself!

[stevenkelby]

Does one of these look like it would work? I haven't gone thyere and checked the physical size but if it fits would it work?

http://www.jaycar.com.au/productView.asp?ID=RZ6571&CATID=&keywords=22uF&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=

Thanks,

Steve.

[pmackenzie]

That one looks fine, but if I am right and the original is a 10 volt part, it might be too large.
The higher voltage is not normally a problem, but it has to fit in the space available.
From the same site there is a 10 volt part :
http://www.jaycar.com.au/productView.asp?ID=RZ6553&CATID=51&keywords=&SPECIAL=&form=CAT&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=871
The dimensions of both parts are listed, so you should be able to check.
What happens when you try to use the rcvr? Does it work at all, or does anything get warm? Do you have a voltmeter?

Pat Mackenzie

[stevenkelby]

Thanks Pat.

I will get one and try.

Will also need some wick I think, never solered that small but have read you need solder sucker and some wick to keep it clean.

In these dimensions:

Case Code-B L-3.5±0.2 W-2.8±0.2 H-1.9±0.2 S-0.8±0.3 W1-2.2±0.1

I'm assuming:

Case Code-B L-3.5±0.2 Means length

W-2.8±0.2 Is width

H-1.9±0.2 Is height


But what does this mean? S-0.8±0.3 W1-2.2±0.1


I haven't tried the rcvr yet but was told nothing happens at all.

I will plug in a batt. tomorrow and see if anything gets warm.

I have a voltmeter and plenty of tools, I will measure the size of the cap. on the board tomorrow too.

Thanks for all the help.

Steve.

[pmackenzie]

Not 100% sure about the last two dimensions. Probably something to do with the size of the electrical contacts on the ends.
Solder braid is handy for cleaning off the solder on the pads before putting on the new part. This will allow it to sit flat.
Be sure you have some fine electrical solder as well, not lead-free plumbing solder.

This thread probably would have gotten more traffic in the DIY electronics section. Lots of experts over there.

BTW I have replaced the same two components on a JR rcvr.
I don't remember where I got the replacement voltage regulator, but it might have come from an old PC peripheral.
The rcvr still works perfectly.

Pat MacKenzie

[z-matrix]

in this case you were lucky, cause' the ripple current caused the capacitor to fail (too much power dissipation, because of too high ESR),
if you want to make it more reliable, solder another capacitor in parallel, (same type, size)

that circuit might not take the reverse polarity...

[pmackenzie]

in this case you were lucky, cause' the ripple current caused the capacitor to fail (too much power dissipation, because of too high ESR),
if you want to make it more reliable, solder another capacitor in parallel, (same type, size)

that circuit might not take the reverse polarity...

Ripple current from what exactly? This is a rcvr, not an esc.
Pat Mackenzie

[Gary Warner]

It looks to me like the rcvr battery was connected backwards...

Pat MacKenzie

Yup, reverse polarity ;)

Gary
--

[stevenkelby]

Well I finally soldered on the new cap. but now I forget which way the battery goes and don't want to fry it again before I give it back!

When I figure out which way it goes I will test that it works and put a + and a - on the label then shrink wrap it before I send it back.

Any idea which way the batt. connects? egblack wire on the left or right in the pic below.

Does the soldering look ok? First go at PCB's but it's on there good.

[coro]

As + is in the middle of servo/rx pack connector, it is not harmfull to connect it in reverse. Harmfull is only overvoltage or misplacing - moving the connector (left or right by 1 pin).
You can try it, and see it this RX will work (if it is OK after burning the capacitor..)

[Zlatko]

What coro said,

but also from your photos I note that the signal pins are towards the new part you soldered, so -ve will be on the outer edge of the PCB. Plus, on the last photo above, the big capacitor -ve end connects to the outer pins ( on the left of that photo ).

BTW, I wish there are more people on ebay like you.
I agree with both Gary and z-matrix, reverse polarity ... but how ....
I hope it works and there are no other problems.

Cheers

[Hell-e-Guy]

Be careful,
If the demux is 74HVC164 based it will not like the voltage on an output pin without any VCC to it if connected the wrong way.
The (+) is always the middle pin as said before.
To find the (-) you just need to find the pins they are soldered together with a simple DVM.All (-) pins are tied together.
I suggest that you try the outer pin first for the (-), (closest to the PCB edge) the inner pin is closer to the demux so it usually easier to route the signal to it.

Good Luck !

[z-matrix]

Ripple current from what exactly? This is a rcvr, not an esc.
Pat Mackenzie

there is ripple current at high frequencies in a tx, and inductive kickbacks can occour that can kill a tantal capacitor easily, i whould connect some low esr capacitors in parallel with the ta+ capacitor, a 10 nF NPO and a 1 nF NPO, (possibly a 100nF ceramic too.)
was it a 10V ta+ ? what power supply was it run with?

i have read the edited first post again, at a second look, it might be some over voltage that killed that capacitor, i was wondering if other circuits could survive.
I whould recommend heat reflow, but only for an experienced engineer.
( this whould take ~5 minutes )

[pmackenzie]

there is ripple current at high frequencies in a tx, and inductive kickbacks can occour that can kill a tantal capacitor easily, i whould connect some low esr capacitors in parallel with the ta+ capacitor, a 10 nF NPO and a 1 nF NPO, (possibly a 100nF ceramic too.)
was it a 10V ta+ ? what power supply was it run with?




Even if I were to believe that there was enough ripple on the supply to damage the input cap, why would you suggest a capacitor with an NPO temperature coefficient?
That makes no sense in this application.
Once again, this is a rcvr. Like almost all R/C rcvrs it runs on 5 volts. Either from a rcvr battery or from the BEC of an ESC.
IMO you are just adding confusing comments to this discussion.
Pat MacKenzie

[z-matrix]

Even if I were to believe that there was enough ripple on the supply to damage the input cap, why would you suggest a capacitor with an NPO temperature coefficient?
That makes no sense in this application.
Once again, this is a rcvr. Like almost all R/C rcvrs it runs on 5 volts. Either from a rcvr battery or from the BEC of an ESC.
IMO you are just adding confusing comments to this discussion.
Pat MacKenzie



no it is not for temperature coefficient, just for dielectric type, and not instead, in parallel, i whould also think about that rcvr is connected in parallel with an esc that generates high ripple current.
i wanted to recommend more capacitors in parallel for lower esr at different frequencies, additionally i whould use a low pass pi filter on an rcvr, if there isn't any, but nwmnd

gone to lunch

[stevenkelby]

Thanks for all the help you guys,

I hooked it up but couldn't get it working...

I have a multimeter and stuff but don't really know what to look for.

All the centre pins have 6v (through the Medusa 6V BEC on my Trex) but the signal pins all get about 1.9V when I weasure the neg. and signal pins.

Any ideas what to check?

Thanks,

Steve.

PS,

Zlatco,

Do you have Paypal, an address and the ability to try and fix it? (hint, hint)

[coro]

All the centre pins have 6v (through the Medusa 6V BEC on my Trex) but the signal pins all get about 1.9V when I weasure the neg. and signal pins.

Is it really dead? With ordinary DVM it is possible that pulses on output pins will make DVM to see some average voltage (just like 1.9V mentioned..).

[stevenkelby]

Yeah thats possible, it's a cheap DVM, and I have strobe lights on the heli that may affect the V.

What voltage would the signal wires output if it's working?

How can I check that the Rx is seeing the Tx?

[Keith43221]

plug in a servo.

[z-matrix]

stevenkelby,
What is the supply current? You connect the amp meter in series, and you can measure with your DVM. Too high, or too low is bad.

---How can I check that the Rx is seeing the Tx?

While running, switch on a tx, if current varies, then it gets the signal.
( the best whould be if it whould work, but if it does not... )

---What voltage would the signal wires output if it's working?

Digital outputs should always be a logic low level, or logic high level, if its changing continuously you can only see a kind of average on your DVM.
50% duty cycle is about 0.5 logic voltage with a DVM.
You whoud need an oscilloscope to verify a waveform.
But if its working it whould be working no? You plug it in and control.

Do you see burns, or holes on any of the ics?

How much does it worth? Maeby it is not to fix it. (dead)

[stevenkelby]

Thanks Keith but I did that, it twitched when first connected to any channel but then wouldn't move with any stick movements. Should have mentioned it.

I know the aervo's good.

Any idea what V I should see at the big Cap next to the pins or at thee V regulator?

[Hell-e-Guy]

Looks like the guy fried it.
What ICs do you see on the PCB ?
74VHC164 ? TA31136? any IC starting with EL ?
Need more info to help you

[pmackenzie]

Any idea what V I should see at the big Cap next to the pins or at thee V regulator?
It is a bit hard to figure out without the rcvr in hand, but here is my best guess.

[stevenkelby]

Thanks Pat,

The first 2 are right but the 3rd one is only 1.13 V

Is the voltage regulator stuffed?

What do the numbers on it mean!!!

Where would I find one here?

https://secure4.vivid-design.com.au/jaycar2005/productResults.asp?FORM=KEYWORD

Thanks,

Steve.