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Samsung Camera SNP-5300 SMPS problem

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2PAC Mafia

Member
Hi guys,

I´m repairing this camera which had water inside. I repaired some problems on tracks due to water and I also found a shorted diode (D14).

The power supply had cycling symptons until I found a broken track from one side to the other of the board, this was at the feedback side so that behavieur was normal as it didn´t get the feedback voltage. The PWM IC is TPS23754.

After repairing those things I get normal and good 12V at the only output of this transformer, the problem is that D14 is getting too hot. You can see D14 at a quick and partial schematic I made. I have tested all components at primary side and I don´t see any bad one. Which could be the reason for getting D14 so hot? I think if I leave more time it will be damaged again. Thanks for your help.
 

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vtech

Active Member
camera which had water inside
Water is the number one enemy of destroying pcb's---especially when there is no conformal coating and any type of salt involved. SMD and sided boards are even worse. Corrosion on the on Eyelets is another problem.:banghead:

Short of removing every component/connector and washing the entire board which is impractical, you are asking for trouble.
Even if you do get it going, it would be a matter of time before something else will quit.

No doubt, your efforts in small business are commendable but your time would be a lot more profitable repairing non water damaged boards----(I used to have a (non marine) repair business---saw many many water damaged cameras).

Most often, due to corrosive nature of salt, there is conduction in-between points and no telling of eyelets etc... visual inspection is the only tool.
Telltales are definitely there.
Good luck.
cor.jpg
 

2PAC Mafia

Member
Hi,

What diode have you used for R14?
I put original diode because in fact they gave two cameras, but one of them was in very bad condition so I didn´t accept to repair. I took a diode with same reference which I would say is S3 code:

http://www.s-manuals.com/pdf/datasheet/s/d/sd101aws,_sd101bws,_sd101cws_tip.pdf

Water is the number one enemy of destroying pcb's---especially when there is no conformal coating and any type of salt involved. SMD and sided boards are even worse. Corrosion on the on Eyelets is another problem.:banghead:

Short of removing every component/connector and washing the entire board which is impractical, you are asking for trouble.
Even if you do get it going, it would be a matter of time before something else will quit.

No doubt, your efforts in small business are commendable but your time would be a lot more profitable repairing non water damaged boards----(I used to have a (non marine) repair business---saw many many water damaged cameras).

Most often, due to corrosive nature of salt, there is conduction in-between points and no telling of eyelets etc... visual inspection is the only tool.
Telltales are definitely there.
Good luck.
Thanks for your recommendation, I know what you mean and I´m agree. In this case I already repaired some boards at this sailing yacht. I accepted to have a look on the camera problem too. I decided to clean it and look for power problems as I can´t check Ethernet communication issues until they install it back on board. My job a lot of times is risky when I decide to repair the units because once you accept to repair you never know the final result. Units with water or salt are always difficult but I don´t repair them so often.

In this case I only want to repair this part of the power supply and try it on board. I never faced this kind of problem with primary diode so I´m not sure the reason for this overheating. If after solving that the camera doesn´t work properly I won´t go deeper in troubleshooting.
 

tomizett

Active Member
Thanks for taking the time to trace the schematic.

I don't really understand what's going on in that snubber network (it looks a bit unusual to me) but C29 and C28 seem a bit small... I don't know if that points to some kind of problem in that area? I can''t see why one/both of these failing low-value would cause D14 to overheat though.
 

2PAC Mafia

Member
Hi Tomizett,

there is a fault in the schematic, C28 is going to source of mosfet. What I´ve tried is to replace D14 by another diode more powerful and see what happened, I used these ones:
1N5408
FR207
MUR460
HER204G

With all of them the power supply output is going up and down a little bit, less than 1V but with the original one it´s stable. I want to be sure what type of diode is this RG S3J2 to put one with the same functionality but more powerful. I´ve seen it can be also SMAJ58A but I´m not sure if it´s matching in this snubber network.
 

tomizett

Active Member
I would have thought that the parameter most likely to cause trouble here is the reverse recovery time. So as long as the diode can handle the voltage and current, the faster it can recover the better.
Do others agree?
 
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