Accidently connected polarity wrong to a metering panel PM438

[ZeTeX]

Hi,

I've accidentally connected a metering panel power supply backwards, so the + and - of the supply got connected to the - and +, unfortunately the meter didn't survive that and just stopped working, nothing smoked but I don't see anything on the display.

Is there a way to fix it maybe? I don't have a schematic and I'm not sure what IC they are using as it is a chip on board.

[Signal32]

Post pictures of the front/back of the meter PCB for better suggestions.
One thing to easily check is to see if the voltage regulator on the meter is blown, check to see if it actually does have an external voltage regulator and check input / output voltages.

[ZeTeX]

Post pictures of the front/back of the meter PCB for better suggestions.
One thing to easily check is to see if the voltage regulator on the meter is blown, check to see if it actually does have an external voltage regulator and check input / output voltages.

the other side is just the LCD display itself.
I dont see any voltage regulator, only resistors and capacitors and the IC.

[Gyro]

That's an ICL7106 (or equivalent) based meter. They don't normally have a voltage regulator as their input voltage is fairly flexible (9v battery range). I don't see a reverse protection diode either. If you really want to keep it, you could remove the glob-top IC in the centre and solder a new one to the pad footprint, but whether it's worth it depends on how cheaply / easily you can get a replacement.

[ZeTeX]

That's an ICL7106 (or equivalent) based meter. They don't normally have a voltage regulator as their input voltage is fairly flexible (9v battery range). I don't see a reverse protection diode either. If you really want to keep it, you could remove the glob-top IC in the centre and solder a new one to the pad footprint, but whether it's worth it depends on how cheaply / easily you can get a replacement.

How do you desolder \ remove the glob? do you need something special?

[Gyro]

That's an ICL7106 (or equivalent) based meter. They don't normally have a voltage regulator as their input voltage is fairly flexible (9v battery range). I don't see a reverse protection diode either. If you really want to keep it, you could remove the glob-top IC in the centre and solder a new one to the pad footprint, but whether it's worth it depends on how cheaply / easily you can get a replacement.

How do you desolder \ remove the glob? do you need something special?

The glob is epoxy so I would think a smelly poke with a hot soldering iron might do the trick. It might be a bit time consuming though as you need to get it flat to be able to solder on a new chip. The die would probably come off the same way, make sure you clear all the bond wires to avoid shorted traces.

I really wouldn't consider it until you've priced a replacement 7106 and made sure it's less than a replacement meter. Nothing to lose at this point however.

Edit: just a quick check on ebay and the one listing for the PM438 is quite pricy whereas chinese ICL7106s are quite cheap. I don't know where you bought it though.

[Ian.M]

+1 for digging with a very hot OLD soldering iron bit.  Don't use a good one!

I'd mask off everything except the blob with aluminium foil over cartridge paper as a thermal barrier, taping down in a square round the blob with aluminium foil tape, (or Kapton tape if you stock it) so you don't mess up anything else on the board.

Use some small fragments of lump Rosin to improve heat transfer to the Epoxy.  It also attacks and softens epoxy when boiling hot, so keep on scraping off what's loose and adding a little more Rosin.

Get the board cleaned up (or fail) before ordering any parts!

[Gyro]

Just one other thought - don't cook the LCD on the other side of the board. Hopefully it's spaced off sufficiently.

[Brumby]

This is something I've never thought about - but I have to ask: How practical is it to try to replace a COB IC?

[Gyro]

I think we're hopefully about to find out, I'll be interested to see the result too. Please document and show us pictures ZeTeX. 

[Ian.M]

Its impossible to replace a COB without a wire-bonding machine. but the O.P's board also has a footprint for a conventional SMD package, so all that has to be done is get the COB 'blob' and die off without b----ring up any tracks that go to vias under the blob (if any) then make sure its been cleaned up flat with no residual bond wires.

[Brumby]

... and a bit of detective work to figure out Pin 1?

[Audioguru]

It is a cheap Chinese meter. Why not simply replace it??

[ZeTeX]

That's an ICL7106 (or equivalent) based meter. They don't normally have a voltage regulator as their input voltage is fairly flexible (9v battery range). I don't see a reverse protection diode either. If you really want to keep it, you could remove the glob-top IC in the centre and solder a new one to the pad footprint, but whether it's worth it depends on how cheaply / easily you can get a replacement.

How do you desolder \ remove the glob? do you need something special?

The glob is epoxy so I would think a smelly poke with a hot soldering iron might do the trick. It might be a bit time consuming though as you need to get it flat to be able to solder on a new chip. The die would probably come off the same way, make sure you clear all the bond wires to avoid shorted traces.

I really wouldn't consider it until you've priced a replacement 7106 and made sure it's less than a replacement meter. Nothing to lose at this point however.

Edit: just a quick check on eBay and the one listing for the PM438 is quite pricy whereas Chinese ICL7106s are quite cheap. I don't know where you bought it though.

Alright, I'm going to use an crappy tip on my soldering iron and setting it to the max tempeture, I'm also going to put an tape over the board so nothing will be damaged.

The metering panel is dead now, so I cant ruin it more, might not work out but who cares, 7106 cost nothing compare to this panel which the only seller that ship to my country is this one:
http://www.aliexpress.com/item/Digital-panel-meter-DC-voltage-measurement-Digital-LCD-header-PM438/32517120449.html?spm=2114.13010608.0.81.cwalhu
and I also need to wait about 2 weeks to receive it.. if I can fix it for a couple of cents with a chip that my local electronic store probably sells then why not.

It is a cheap Chinese meter. Why not simply replace it??

its not that cheap. its 16$ for 5 of those - ~3.2$ for one - but there is only one seller that ships to my country and he is from hong kong so a lot of waiting time. also minimum order is 5..

+1 for digging with a very hot OLD soldering iron bit.  Don't use a good one!

I'd mask off everything except the blob with aluminium foil over cartridge paper as a thermal barrier, taping down in a square round the blob with aluminium foil tape, (or Kapton tape if you stock it) so you don't mess up anything else on the board.

Use some small fragments of lump Rosin to improve heat transfer to the Epoxy.  It also attacks and softens epoxy when boiling hot, so keep on scraping off what's loose and adding a little more Rosin.

Get the board cleaned up (or fail) before ordering any parts!

I will try aluminum foil + cartridge paper, hopefully it will work.
I don't have rosin

Just one other thought - don't cook the LCD on the other side of the board. Hopefully it's spaced off sufficiently.

hopefully it wont happen. there is not much I can do about it but I will try my best to not get too much heat.

I think we're hopefully about to find out, I'll be interested to see the result too. Please document and show us pictures ZeTeX. 

I will!
Thanks for helping everybody!

[ZeTeX]

Well I managed to remove the COB, no vias where damaged.
I think its ready for a new IC.
it was ugly but at the end I managed to remove it pretty cleanly, I think with some practice and right tools I will be able to remove those without a lot of mess.
and the smell..
http://imgur.com/a/ipsCs

[Gyro]

Well done ZeTeX it looks like you had fun. Thanks for posting the images.

Well I did warn you about the smell... though in your case I reckon it was mainly the plastic surround!   

It looks as if you're in good shape to buy a new 7106 now. 

[batteksystem]

That's an ICL7106 (or equivalent) based meter. They don't normally have a voltage regulator as their input voltage is fairly flexible (9v battery range). I don't see a reverse protection diode either. If you really want to keep it, you could remove the glob-top IC in the centre and solder a new one to the pad footprint, but whether it's worth it depends on how cheaply / easily you can get a replacement.

That is not an IC, it is a wire-bonded die inside it. I would say buying a new one would be a far easier job.

[Brumby]

That is not an IC, it is a wire-bonded die inside it.

Ahhhh.... the die is the IC.

It's just not encapsulated in a standard package like SO or DIP - but rather by a blob of black stuff on one side and the PCB on the other.

[batteksystem]

That is not an IC, it is a wire-bonded die inside it.

Ahhhh.... the die is the IC.

It's just not encapsulated in a standard package like SO or DIP - but rather by a blob of black stuff on one side and the PCB on the other.

You're right, just I always treat the wire-bond die and DIP/SMD IC as two complete different things, as the manufacturing process are very different.

[mikerj]

You're right, just I always treat the wire-bond die and DIP/SMD IC as two complete different things, as the manufacturing process are very different.

The manufacturing process of the die is exactly the same, because it's the same die.  Instead of wire bonding the die to a lead frame and encapsulating it, you wire it to a PCB and encapsulate it.

[batteksystem]

You're right, just I always treat the wire-bond die and DIP/SMD IC as two complete different things, as the manufacturing process are very different.

The manufacturing process of the die is exactly the same, because it's the same die.  Instead of wire bonding the die to a lead frame and encapsulating it, you wire it to a PCB and encapsulate it.

On the other hand, there are no need to wire bond the die and wait for the epoxy to dry if you use the normal IC. These days except very low cost, very high volume items (watches, LCD, etc) most already use pre-capsulated IC.

[Ian.M]

Lets further increase your confusion!

What about Flip-Chips?
Take a bare die, passivate it, add solder bumps, and  flip it over and solder it direct to the PCB

[Brumby]

Lets further increase your confusion!

What about Flip-Chips?
Take a bare die, passivate it, add solder bumps, and  flip it over and solder it direct to the PCB

I was waiting for someone to throw that one into the mix.... 

[batteksystem]

These days except very low cost, very high volume items (watches, LCD, etc) most already use pre-capsulated IC.

Very high power power electronics use bare dice. The same die, if packaged in a TO247 package, can be rated at 50A, then it can be operated at at most 20A (assuming isolated drain tab heat sink) for long term reliability. The same die in a power module package (AlN DBC+AlSiC base plate) can be rated at 80A+, and operate at 60A.

This would depends on how thick and how good (gold!) the wires you use for wire bonding.

[mikerj]

On the other hand, there are no need to wire bond the die and wait for the epoxy to dry if you use the normal IC. These days except very low cost, very high volume items (watches, LCD, etc) most already use pre-capsulated IC.

This is a low cost item, so I don't really see your point?  The cost of a bare die for a reasonably simple IC is very small so packaging costs can be a very significant overhead.