Turbo Express - no power - AC adapter working

Hi,

My TurboGrafx Express is not powering on. I took a meter and can verify it is receiving power and the adapter works. Can anyone tell me what the component in the picture with the letters "SOC 1A" is? I can't tell if that is melted plastic or left over rosin. I cleaned the board with alcohol. It seems to be the only suspect component... as all the capacitors look good. I didn't notice any bad traces. :shrug:

http://dl.dropbox.com/u/2030008/IMG_1126.JPG

Edit: How rude of me. I forgot to say... any assistance or advice you can provide is greatly appreciated. Thanks in advance.

 

Looks like resin. Check that part and see if you have continuity as its a fuse.

 

Looking at the picture it looks like you have a potential dry joint on the back of the power connecter, the solder looks cracked, this isnt that uncommon , and just needs to be reheated and a bit more solder applied to it.

Might be wrong but that is what it looks like on the picture,at that angle its a bit hard to tell.

 

I was pretty sure it was a 1 AMP fuse. But, I have not seen one like that before. I had checked continuity at it... and it seemed hit or miss... which was confusing to me when I first assumed it was a fuse. I will check again... as well as check the power connector. Maybe take a couple more pictures. Thanks guys, I will get back to you after work today.

 

You would probably need to clean the leads/pads to get a reliable reading. Probably have some oxidation going on, which means you may have trouble getting a reading.

If it shows as having continuity then loses it, its probably fine and just the surface you are probing that is the problem.

 

Yes with the switch in the 'On' position, you should get continuity from one of the pins on the DC jack to the fuse itself. I agree the soldering on the DC jack does look a bit suspect.

If you haven't done so already, use the continuity mode on your multimeter as it'll make a beep sound when the circuit is closed.

 

Okay. Here is where my laughable expertise fails me. Continuity exists with the ground across the entire board, as it should. But, with the circuit closed I cannot get the fuse tone on either side from a test of the positive or negative of the DC jack. But, what I don't understand... is if I place one of the testers on the battery positive (not DC jack) and one on one side of the fuse I receive a tone... but, not the other side of the fuse.. whether switch is set to on or not. So, I would think that the fust is bad... But, why wouldn't the same thing occur with the DC jack... and why does it do it whether the switch is open or closed?

Though, I should mention I had already tested it with batteries alone before starting this endeavor. And the express did not power on with either jack or batteries.

I tested the back of the DC terminal to the inside post... which tones fine. As well as the side post with the inside of the jack.

 

If you place the multimeter either side of the fuse you should get a tone (or a reading of 0ish ohms), if you do then the fuse is fine and something else is buggered. If you get no tone (or a reading of infinity) then you could you could bridge the fuse and see if the unit comes on, if it does not then something else is buggered.

 

Thanks, guys... I appreciate the help... though, I do know how to test for continuity. And I am sure I what I wrote is confusing as hell... though, it makes sense in my brain.

The fuse does not tone when the probes are placed on either side of the fuse and it does not tone when a probe is placed on the ground or positive and to the powered side of the fuse... and I am pretty sure the fuse is bad. But, that still doesn't answer the other issues as well. Tones when touching the powered side of the fuse and a probe at the positive side of the battery case... whether switched on or off. But, no tone when touching the positive or negative of the DC jack and the powered side of the fuse... whether switched on or off. Though, tested the DC jack and solder points under the board and they toned and were showing voltage when power was applied.

Also, switch tones when DC jack ground is probed and the ground on the switch probed. But, Jack positive and switch positive does not. Bad switch and fuse, possibly?

 

Just testing the sides of the fuse is enough to tell you the fuse is blown, the rest of it is not going to tell you anything. The power jack and switch (DTDP) are easy to check, if you can't check this then you probably should not be in the side of a console. Although I think a simple reflow of the solder would probably fix them as they probably have loose or dry joints.

I personally would bridge the fuse, stick some batteries in and turn it on and see if it comes on, if it does then you can either leave it bridged or fit in a 1A fuse (any will do).

 

I tend not to bridge fuses (or recommend it) - they blew for a reason, something else might need repairing and you wont really know until you test it with another fuse in.

Id just solder wires to either side and use a "normal" 1A fuse. If it works, you can look at replacing it with a SMD one (or choose to leave it ghettoed up).

 

Once again. I appreciate any help. Yes, I know how to test a switch, and a jack.

But, you guys are right. One step at a time. Replace what you know, and work down from there. I had 2s and 4s at home... so, I am going to grab some 1Amp fuses on the way home from work. I mean, it most likely would have been safe to test with 2A fuse... But, I had only verified voltage on the AC adapter and not Amperage. Could have a failed resistor in the adapter.

But, Yeah... back to point. I agree with not bypassing the fuse. I will grab some and let you know. Then, I can worry about the switch, and jack. :Rock:

 

Or 7805 if they have one.

 

Sorry, for the delay. I replaced the fuse and the LCD powers on. But, that is all. No sign of life from the system itself. Brightness pot does not change brightness... and the system itself does not make a sound. I have gone over the entire system... and repaired the dry solder spots I saw and tested most of the traces. They seem good to me. Might be a lost cause at this point.