Short near max77420

[rickster26ter]

Hey guys. I have a switch OLED that won’t turn on. I fixed several things to get to where I am. I am getting about 15V agreed voltage when I plugged my switch in, but about 12 mA of current draw, indicating a short somewhere. I checked my voltages at the max77620, and noticed a couple things.

On the bottom left cap I’m getting 1v8 when the switch is on instead of 1v. On the bottom middle I noticed a short at the cap. I took the cap off, and am still getting a short on the bottom side (that looks like leads to caps underneath CPU). Not sure where to check from here.

Not sure why I cant embed media items, nor include links in a post? So it’s hard to explain more without those…

Thanks!

[rickster26ter]

[jkyoho]

Assume you could tell the picture is from v1 not even v2 or OLED, the ground/short you found is just low impedance at the cpu voltage line. Typical resistance reading is about 20 ohm on v2 or OLED

[rickster26ter]

Nope. I thought it looked different. Thanks for pointing that out thanks, that helps a lot! Ok, yea I’m getting 17 ohms there. So that looks good for the bottom cap. I guess my next location to look would be trying to follow that bottom left location? I’m going to put that cap back and try to get updated voltages for everything.

[rickster26ter]

Sorry, I also realize the picture I attached above isn’t the voltage you should be getting, but giving you the current you would get if injecting 1v.

Here are the voltages I am getting when plugged in.
Hoping someone has any ideas on where I can go from here.

Thank you!

[rickster26ter]

And my current draw:

[Severence]

Charge current seems low, check your battery is connected. After, disconnect battery and power and check the USB fuse. If all good then check USB continuity with a breakout board to/from continuous locations.

Avoid following the retrosix wiki, it’s bad info in almost every area.

[rickster26ter]

I want to start out by saying thank you to Severance and Jkyoho, in my noob stage where I cant post for 24hrs I have been reading a lot on here, and you guys have done the brunt of the help here, so thanks a lot for lending your expertise.

Some background on this, I got this OLED working fine. I replaced the screen, and modded it, but then I started having turn on issues. I have not been able to detect shortages with a multimeter, so started doing the shotgun approach (which hasn’t been working out very well) I’ve replaced th bq, max77812, and max77620H. Through that I have been able to get from like 2mA current draw to this 27 or so mA current draw.

Attached is my charged current with the battery plugged in, a little higher. My diode near the usb-c is good, I have checked. I also know since it was bad earlier, and this was drawing only 5v before I replaced it. I replaced it and now I have the 15v agreement.

I have a usb-c breakout board. I started measuring, but for some reason I can’t get continuity for even tx1+/tx2+. I’m not sure why, I never touched the usb-c, but looks good to me. It should just connect straight to the chokes right?

A couple more questions;

Since I know a small amount, but need more knowledge since I’m not clear on components. What’s the max77812 supposed to produce? I see about 4.2v near the smallest caps to it, which I think is the input, and then I see the 4.2v produced on the max77620H. So trying to even make sure that’s working right.

I heard in one post that caps on other side of soc having both sides beep in continuity means a short, but I am also very clear on severance knowing resistance is the better way to check. I am getting 0.2, 60 ohms for one cap I.e, which I think is ok. For other caps I get 0.2, 14 ohms. Is this still good?

Thanks
![1000001325|666x500](upload://1LzJSzWPnFwpxmyAbtQz0G35Qwh.jpeg

[rickster26ter]

[jkyoho]

Seems like typical console stop working after modded. And randomly swapping ic may lead to another loop hole. Appropriate troubleshooting steps are understanding the situation first before doing any change. You dont see any patient going into emergency room and send directly to have brain surgery. Doctors ask and check prior to confirm the situation at present, so is the troubleshooting for most repair job.
Show more close up picture of the area where you have worked on. i.e EMMC aream CMD and clk point. I guess you have a emmc adapter instead of reballing or kamikaze.
FYI, the current draw from charging port varies and depends on the actual battery voltage, if you have a closed to full-charged battery(4.2v), the current draw is expected as low as 0.1A or less.

[rickster26ter]

Sure, I took the mod off to isolate before opening this thread.

CPU:

CPU point:

Emummc

Bq

Max77812

B point

A point:

Max 77620h again:

[Severence]

assuming your battery isn’t undercharged or fully charged then afair approx 0.15A charge current is typical on boards which have an EMMC issue (or if you disconnect the EMMC module) so it seems likely given the mod was present that this is your issue, whether it be physical damage to the EMMC IC itself or partition issues / corruption. So you’ll probably wanna start looking into that first, search the forum for this one as it’s been covered a fair few times

Also spot minor damage to the Max 77812 on the corner, may just be the top coating but worth zooming in on that for confirmation