Orion AC/DC tv/dvd combo won't power on with 12v dc

It's an Orion TVDVD092 9" tv/dvd combo that I use in my camper. IIRC it was connected to DC backwords awhile back, meaning - and + were reversed, at least that's what I think.

Fuses are good and nothing is visibly fried, no cold joints either. Plugging it in to 12v I get power all over the main board that power is connected to, 12v though. With it plugged into AC I get 40V at the same points. I cannot find a schematic anywhere so I'm shooting in the dark here.

I've checked out a few similar sets at local thrift shops only to find the same problem, nothing with DC. Seems a common problem. Not sure if anyone can help but if you have any ideas I'm all ears. TIA

If it has been reverse polarized, then I would suspect a blown diode somewhere in the circuit, may also be blown resistor

Both of which could be blown without visible evidence... without a schematic its a pain, you will have to try to trace the line from the power input testing each diode/resistor you come across.

Good Luck!

Norm (aka warf135)

There's a diode near the 12v input that looks a little suspect, maybe I'll take another look but honestly, without a schematic it's not really worth the effort to me. Thanks though, maybe if I get some spare time I will open it up again.

yes its annoying when you cant find schematics for stuff... you could try looking for a service manual for the item, or try to locate a schematic by the board number inside the set. (many of these cheaper brands use the same insides and stuff)

most cheap multi-meters now have a diode test function on them, so it may be worth testing the suspect diode... or simply replacing it if you have a suitable replacement at hand

Norm (aka warf135)

At the very least, you would want to connect it up to 12V (correctly ) and trace through from the 12V jack through the power supply section. It is most likely that would indicate fairly quickly where the issue is.

It is quite possible that there is a fuse on the board that doesn't look like a traditional glass fuse. There are a number of other threads here dealing with devices having their power applied reversed and if you look for them, you may find some other hints. I believe one of those threads is listed in the "promote a post" thread.