Turbo Duo...from broken, to "fixed", back to broken

[n8great321]

I'm basically at my wits' end with this thing.

I bought a broken Turbo Duo off Ebay.  The seller said it wouldn't turn on and I thought I could fix it.  I bought a cap kit and replaced about 20 of the caps one night, basically everything from the heatsink down and the LED access light left.  Low and behold, the thing powered on! However, without a controller or any games, there wasn't much I could do.

While waiting for a controller to arrive, I went ahead and finished replacing all the caps except two of the through-hole ones by the CD unit (the ones you have to take off the covering thing underneath for).  After I did that, no power.  That's where I sit now.

I've re-done caps I thought I might have messed up.  I've used strands of copper wire to string together parts where it looked like traces were destroyed.  So far, nothing has worked.  I have no idea where to even begin testing, how to test (I have a multimeter), where to narrow down the problem, or even if the thing is repairable at this point.  I'd like to try and repair it myself but if I'm doing more harm than good, I wouldn't mind sending it off to one of the more knowledgeable members of this community if they'd like to help me out.

Any help is greatly appreciated! 

[PunkicCyborg]

this may sound silly but have you checked to make sure your power supply is working and it's the right polarity and amperage?

[n8great321]

Yes I checked it with the multimeter and I'm getting 10 volts.  It's the NEC brand power adapter that came with the Duo.  It worked the first time around, after I fixed about half of the caps.

[wilykat]

Double-check the caps you replaced after the first power on test. Are they in the correct oriention? Reversed electrolyte caps in certain area can prevent system from working.

Also check the solder to make sure it is good. 

[Keith Courage]

Could be a bad 7805 power regulator. I'd change both and see what happens.

[n8great321]

Are there any members of this board who would be willing to have the system sent to them so that they might have a look at it?

[thesteve]

i can fix it for you, but could likely help you fix it yourself.
for starts,what happens when you turn it on.

read this http://www.pcenginefx.com/forums/index.php?topic=12510.0

[n8great321]

I actually have a youtube channel so this video shows off what it was like when it was working...


In that video, I had replaced the fuse and repaired the trace running from the (+) leg of the cap in the lower left (by the power switch, the 470mf one) to the lower-right via immediately next to the power switch.  Now, with all the caps replaced, nothing happens.  I thought it could be a video problem so I put the system top back on, loaded in a CD game, plugged in the controller and pressed run to see if the access light came on or the disc spun.  No luck.

In the so-called "forest of caps" above the voltage regulators, I noticed the via for the (-) leg of C305 was torn up.  It looked like the trace running from the (-) leg of C305 to the (-) pad of C612 on the top of the board was broken so I soldered a piece of copper wire to connect those.  I did the same on the underside from the (-) leg of C305 to the (-) leg of C306.

[thesteve]

it sounds like your on the right path.
the 47uf cap by the power switch is your video output coupling cap.
i see you have a meter too.
recheck the fuse.
if good check for power in and out of the 2 7805 regulators (the heatsinks)
if good so far, the fun begins.
if not, problem solved

[n8great321]

I may re-do the fuse, I'm not getting any mA reading on my meter.  It worked before and nothing has changed? Looking at the fuse, it doesn't look blown.  Can I safely replace it with copper wire for the time being, just for testing purposes?

How would I go about testing the regulators? What two points should I be touching with my meter (and with what leads if that matters)? The metal screws on the heatsinks? One of the screws and another point on the pcb? With the system powered on or no?

I will be out of town for the rest of the week but will definitely revisit the system when I get back and have some time.  I appreciate all the help so far!

[thesteve]

start with ground
your meter should be set to volts DC
ground (the sheild, switch frame, controller port frame) is your negative.
you should have positive (input voltage) both sides of the fuse.
the regulators will have input, ground and 5V pins

[n8great321]

I got identical positive voltage on both legs of the fuse, so that seems OK.

Looking at diagrams online, it looks like the 7805 legs are (left to right) input, ground, output.  It was a tight fit to get my leads in there to test (on topside of board), but I tried it with the (-) lead on the ground pin and the (+) lead on the 5V output and...no voltage reading.  I did the same with the (+) lead on the input pin and no reading either.  It would start with a minimal reading, maybe 2 mV and then quickly go down to zero.  I only tested the regulator on the left since I couldn't fit the meter leads in to test the other one.

Assuming there wasn't any fault in my testing methodology, maybe that's the issue? Now, how do I go about replacing these regulators? Unscrew and desolder, or do I need to take off the entire heat sinks? It looks like Radio Shack carries them so hopefully it's that simple.

[thesteve]

if you have 0V on the input pins then you are losing power between the fuse and the regulators

[n8great321]

Replaced the voltage regulators (including thermal paste) and still no go.  Getting no reading on the input pin.

What's the next step to test/replace?

[thesteve]

trace it back
power inters at P302
goes through diode D301 to fuse FS101.
from fuse to switch
from switch to regulator input pins and cap C301