SNES console, PAL 2-chip, no video and keeps blowing fuses

My PAL SNES developed an issue where it no longer displays graphics. Replaced the caps (not the SMD ones as I wasn't aware it was also required). Still no graphics.

Have tried 2 original PSUs and one aftermarket.

The consoles has blown 4 or 5 pico fuses since the cap replacement.

Output from voltage regulator is 5v.

I hav another set of replacement caps (regular and SMD) on the way, and a capacitance measuring device.

Is it likely that it is a faulty cap causing the fuses to continually blow, or something else?

Thanks.

 

hi bonzo , yes if a Cap is bad it will cause a fuse to blow. You may want to remove what you installed and test them with a DMM , if you find any dud ones dispose of them and check any new ones going in first before soldering them in.

 

Wrong polarity on electrolytic caps is another possible cause

 

Thanks for the info.

I checked cap polarity, all good. I'm guessing/hoping some caps come up bad and that nothing else is busted. Will know more once the new multi arrives next week.

 

I would get the proper power supply plug for it. I once used the SNES power supply plug on my Atari jaguar and smoke came out of it. I had to replace 3 chips init .

 

Your problem isn't with the e-caps, that isn't likely at all.
You have a dead short somewhere, and it draws enough current to blow the fuse.
Measure resistance / continuity between Vcc and ground.
Look for tiny metal splinters on each of the IC pins that may be making contact.

 

Probably mixed a center-positive and center-negative adapter/plug then. PAL snes uses an AC adapter so first thing in the power circuit is a bridge rectifier so he's safe.

 

Cap replacement didn't change the situation at all, was too tired to go inspecting/probing for shorts last night, so Ill check later today.

Forgot to mention in OP, when connected to OSSC with HDR component cable, the sync keeps dropping and the reported Hz rate on the LCD skips around. How does this affect the diagnosis? Doing it before and after cap replacement.

 

I have two official PAL SNES PSU and 1 good quality aftermarket one, they all output sufficient voltage (around 10.5 volts, from memory) which ends up as an even 5V on the output leg of the voltage regulator.

 

Does the power led still come on

 

I've gone over all pins on each chip on the mob. The is current flowing between specific pins, but I checked on my other PAL 2 chip and they are all the same so it appears to be design and not fault.

What's the easiest way I can find out where vcc enters or leaves each chip?

 

You've already finished that test. All I wanted you to check is if there's a short between Vcc and ground.
So yeah, do the fuses still blow? If they do, something that isn't a short inside the console makes it draw huge currents anyway.
Maybe a problem with cables, or the TV?

 

Problem persists with OSSC, Framemeister and CRT via SCART. Using SCART and HDR component cables with the digitizers, and using SCART on the CRT. On the CRT, I can see a picture via RF but it's black and white and super feint/fuzzy. I can make out the shapes of some of the letters from the SD2SNES menu, but can't actually read the letters.

When connected to the OSSC, it gives a HZ reading, but it jumps between different values in starting at 54.4 gradually reducing to approx 53.2 and then losing sync completely. This behavior is consistent the three time I powered on the unit just now. I'm sure if I had the knowledge of an EE this would take least narrow down where to investigate.

I guess I should grab a schematic and trace some of the video lines and inspect the various caps, resistors and such, to make sure they are still behaving correctly.

Or maybe a chip has died and I need to start chip swapping from my other 2-chip.

Or maybe its time to fork out for a scope and investigate like a pro.

Maybe maybe maybe lol.

 

The good schematics are only for NTSC consoles. PAL ones differ on the output. Crucially, the RGB outputs don't use AC coupling capacitors that could go bad.
RGB circuit:

Look if you can find schematics for the Composite Video line!
Or maybe that line is the same as in the nice schematics? If so, there should be a big 220uF (or 2 x 100uF) near the multi AV. Replace it / those!