Turbo Duo Shorted Out - Trying To Fix

[DirtMonkey]

I picked up a Turbo Duo off ebay and trying to get it to work.  I noticed that there was a short on it and a few bad caps.  I started by replacing all the caps initially to get that out of the way and now I am tackling the short.  The short is in the CD-ROM side of the system but I have been unable to track it down.  All the traces visually seem to be fine but one thing I did notice is that the 7805 closest to the CD-ROM runs hot as expected because of the short but also IC501 runs hot.  System will run TG16 cards but will not boot up to the CD menu.  Any idea where to start to track down the short? 

First question, how do I know there is a short?  If I check any cap on that side such as C519 then + and - have continuity.  This was present prior to the recap.

[wilykat]

With ohm meter and the system powered off, check between 5v and ground. You want a few hundred ohms minimum between 5v and ground.  If it's low (under 100), there's a short.

If one chip seems to get hot enough to fry an egg, it may be a bad chip.

[DirtMonkey]

Ok, I have taken a look at the board with my trusted multimeter.  The CDROM side of the board has a short when looking at the OHM resistance between 5v and ground.  In most places it gives a reading of about 1.2.  As mentioned, the C519 chip is REALLY hot when running for a while.  I am sure if I kept it running for longer then you could probably cook an egg on it.  After about 3 mins or so it is uncomfortable to touch.  Everything else runs nice and cool. 

Just for the sake of testing, I pulled all the SMD ceramic caps I put in thinking that perhaps I bridges one but the short is still there with all them gone.  All traces on the board look fine and the only lifted pads I had were on the TG16 side which functions fine. 

Seriously looking at investing in something like a Leakseeker 89 to help identify where the short is in the system.  Might come in handy for the future too. 

I am sure if I sent this to one of the senior guys on here then they would be able to figure it out without much effort but there is no sense of satisfaction if I don't find it myself.

[thesteve]

most sections of the system run power chokes (SMD) with 22UF caps after them
in case of short the chokes tend to open acting as fuses, so anything after a choke can be ruled out

[DirtMonkey]

thesteve, I have read a lot of your posts on here and I know you are kinda the master when it comes to these systems.   I am trying to understand your post but I am a bit lost.  Am I to understand that if the power is going through the chokes then the short is obviously after those points?  I had pulled all the 22uf SMD caps thinking that I may have bridged one of them and it make no difference to the short.  I was still getting continuity between the 5v and ground even at the 7805 which is the beginning of the circuit.

I am getting very close to sending this board out to one of you guys for checking it out but since I am in Canada, I would still prefer to find it myself.

[thesteve]

all the 22uf caps behind the card slot have a ceramic cap and a choke hooked to them
power goes from the regulator through the choke to the caps
the choke looks like a ceramic cap, but is marked with an L number instead of a C number
it has a small resistance to it as well, so checking ohms to ground from different 5V points in the system should get you close
the traces even have some resistance, making that apply there as well

[DirtMonkey]

The resolution of my crappy automotive multimeter sucks so it is very hard to pinpoint but it looks like I was able to isolate it to around C501.  Just for shits and giggles I removed L501 to try and isolate the short.  Well, everything before L501 is no longer shorted out.  It is also IC501 which is the only component, besides the regulator, that gets hot enough to cook an egg on.  Everything else on the system is running cool. 

FYI, I have ordered up a nice Fluke multimeter with a lot better resolution.

[thesteve]

well if IC501 is cooking it needs replaced

[DirtMonkey]

Yeah, that is the scary part.  Lots of pins on that guy but I am thinking it has to be the problem.  I have a new torch element coming in next week so I will have to wait till then to pull the chip.  How does one go about finding a replacement?  I have tried to search for the part number online but haven't found anything yet.

Have you ever seen one go bad before?

Lastly, is there any schematics for the Turbo Duo kicking around?  I can't seem to find any online.

[DirtMonkey]

Where do you guys source out the parts?  You can't seem to find dead systems on Ebay anymore without paying an absolute arm and a leg for them.  Does this system BECOME a donor system now?  So sad.

[thesteve]

dead systems is the only option as its a custom chip
seen several go bad

[DirtMonkey]

dead systems is the only option as its a custom chip
seen several go bad

Thanks my friend.  I will have to put it in a bin until I find one.   Sucks to get this far and hit a wall.

[wilykat]

Bummer