Accidentally plugged in to a 12v adapter, won’t boot

[Dclowd9901]

I figured I’m screwed but thought I’d check here first to see if there’s any where on the board I can check for a fuse or blown cap in case too high a voltage is supplied. Or maybe a jumper to throw the unit back into recovery mode? I have the v1.6 OSSC (not a DIY build).

[Morpheus_79]

The fuse F1 behind the 5V barrel jack input is rated for 32VDC/1,5A. That’s why it won’t protect your OSSC from damage caused by an accidentally connected 9V or 12V power supply. So the 12V from the power adapter most likely killed the voltage regulators U5 & U6. You could check if one of them or both short the main power supply line to ground like it’s described here (Verification -> 1.):

https://github.com/marqs85/ossc_pcb/blob/v1.6/assembly/assembly_tips.txt

[Dclowd9901]

Thanks for the help, Morpheus.

I went through the doc you sent and checked the voltage regulators. All (strangely to me), registered continuity through _all three pins_ to ground. I was looking for one to be the problem. Is the circuitry such that if the “first” in the chain of regulators failed, all of them would show this failure?

[Morpheus_79]

U5 and U6 are both connected to the main 5V input rail. If one of them has its input pin shorted to ground you can measure that short on the other one too. I would recommend replacing both, since i can’t remember any case where only one got damaged from a connection to the wrong power adapter. They only cost a couple of cents and are easy to get. But replacing U5 could be a problem though, since it’s nearby the lcd display (which has to be protected from the heat of the hot air station -> i used a combination of kapton and aluminum tape in the past… which worked pretty well).

The inputs of U7-U16 are connected to the 3.3V output of U5. So if the output pin of U5 is shorted to ground the input pins of U7-U16 seem to be shorted to ground too. In the worst case some of them could be damaged too. You can’t rule that out.

Since the HDMI transmitter IC IT6613 (U3) is connected to the 3.3V output of U5 too, there is a possibility that it has been damaged too. But you can check that only after repairing the voltage regulators. If U3 is broken too the OSSC will start as usual… but gives you an ‘Init error -4’ on its lcd.
U3 is pretty cheap too… and it’s the easiest one of the three biggest ICs to replace (since it has no big ground plane on the underside)… but there is still a lot more soldering experience required than for replacing the voltage regulators.

[Dclowd9901]

Great — I guess I’ll start the process. Appreciate the help.

[Dclowd9901]

Yikes — so, at least according to Mouser, the 200mA Voltage regulators are backordered til Jan 2022… think I’ll just order a new unit. Thanks anyway.

[Morpheus_79]

Possible replacements:

U6:
TPS79933DDCT

U13:
TLV70025QDDCRQ1

U15/U16:
TLV70018QDDCRQ1

[AetherSmith]

If it’s alright for me to piggyback on this topic, I’m dealing with the aftermath of a nearly identical screw-up. Protip for anyone who owns a gscartsw! The adapter may look identical, but DON’T under any circumstances let them get mixed up. The gscartsw uses a 9V supply…

When checking U5 and U6 as described, should position of the power switch affect readings? When the switch is turned on for mine, the input pins on both (and the enable on U6) show up as shorted to ground, but with the switch off only the ground leg of each shows a connection.

[Morpheus_79]

There are a diode (D5) and a 47µF capacitor (C107) connected to the 5V line between the barrel connector for the power input and the power switch. If the diode or the capacitor is broken it may create a short between the power rail and ground right in front of the switch… so you’ll only see this short if the switch is in the ‘on’ position.

I would recommend: put the switch in the ‘off’ position and check if both pins of D5 or C107 are shorted. If they are: remove D5 first (because a broken diode is more likely) and check again after that.

[AetherSmith]

Thanks, that actually explains some behavior I’ve been seeing quite well! I confirmed that D5 was showing up as shorted, and after removing it U5 and U6’s inputs no longer show as shorted to ground with either switch position.

Is it safe to do a test power-on without D5 in place? I’m not the best at circuit design, so I could be completely wrong, but it looks like it’s just there to prevent damage in case the wrong polarity of adapter is used?

[Morpheus_79]

If you make sure there are no shorts on any of the voltage regulators and if you take care to plug in the right power supply with the right polarity it should be safe to test.

[AetherSmith]

Alright, thank you! I’ve confirmed that with D5 removed, the OSSC operates normally. Seems I got really lucky here.

Looking towards replacing the diode, it appears to be out of stock everywhere at the moment. Can you tell me what specs I would need to look for in a replacement?

[Morpheus_79]

Mouser still has those SD05-7 diodes in stock. Substitutes: SZSD05T1G, SD05T1G or SD05T3G.

If you’ll have to buy from somewhere else: try looking for the same working and similar breakdown and clamping voltages in the same package.

[AetherSmith]

Oh, haha, it seems it literally came back in stock since yesterday! Thanks again for you help!

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