Update 7805 to OKI-78SR-5 for heat reduction

[Fidde_se]

I don't care much for the heat issue but there is a much more important factor here and it's the factor that sometimes the 7805 breaks and shorting inside and letting the input voltage go directly to the output, and with it burning every circuit and carts/hucard you put in it.. How many games would you try before you realise it's acctually killing them? It's not what you first would expect, just some dirt on the cart right? Let's try another one...

I don't know if this particular regulator has this protection built-in, it of course depends on the quality of the 7805 to begin with but I'v seen this happening on famicoms on several occasions.

[NightWolve]

Yeah, that's a great point to raise. So definitely, I would recommend replacing your 7805 regulators on 15 to 20-something year old systems! The older they are, the closer to burnout they are! In the meantime, make sure there is fuse protection, that's precisely what it's for!!!

My SNES suffered from a 7805 breakdown/burnout, that's why my fuses kept popping, and when I ran out of 1 amp fuses, I tried a higher rated one after believing I solved a shorting problem, I was wrong though... As a result, one of the SRAM chips was damaged since the full 10-12 VDC from the power supply was sent into the motherboard for a split second... :/

I since fixed the system by desoldering the 7805 and implementing a 5 VDC mod, where my external power supply is a hacked 5.31 VDC 2 Amp, regulated model. It's an even 5 Volts after passing the power switch and hitting the motherboard counting the wire resistance and length, etc. So no more heat sink inside the SNES, regulation is all outside and this model is pretty sophisticated, so I'm betting it probably has protection. Nonetheless, I soldered 2 metal clip holders for standard glass fuses and bought a 40 pack from eBay, so the fuse protection is back with proper rating. SNES normally has a ridiculous one-time fuse that has to be resoldered off/on, it looks like a diode/resistor.

ProTip: Your TurboDuo has a 3 Amp fuse by default, but it's highly recommended to replace that with a 1 to 1.5 Amp fuse as 3 Amps is WAY too high and something might get damaged in a breakdown situation like this!

[Vimtoman]

It may have a 3A for inrush current reasons.

[NightWolve]

Desh had been running his with a 1 Amp per the "turbo tip" mentioned, wasn't sure if that was too low though and would need to be replaced with a 1.5 Amp as that's what the SNES uses, but the lower the better if it works out.

But yeah, you don't want to get stuck with too low of a choice and have it be popping all the time. The maximum stated draw is 1000 mA on the Turbo Duo power supply, and I thought I read from Steve the draw of the system was at ~850 mA, not sure, so a 1 Amp fuse could be OK in principle, but a safer bet would be a 1.5 Amp fuse and for the issue you mention.

Pretty sure Desh reported it worked out, but longer testing and by more people would be needed to learn if it really should be at 1.5 Amps instead.

[SignOfZeta]

I don't care much for the heat issue but there is a much more important factor here and it's the factor that sometimes the 7805 breaks and shorting inside and letting the input voltage go directly to the output, and with it burning every circuit and carts/hucard you put in it.. How many games would you try before you realise it's acctually killing them? It's not what you first would expect, just some dirt on the cart right? Let's try another one...

I don't know if this particular regulator has this protection built-in, it of course depends on the quality of the 7805 to begin with but I'v seen this happening on famicoms on several occasions.

That's a good point, I never thought of that, however I'm going to go ahead and wait until at least one other person can prove that this ever happened to them before I replace a part. The odds of this tragedy befalling me seem to be about equal to the chances of me accidentally shoving my soldering iron straight through the PCB; nearly but not exactly zero.

Some guys here have refurbished dozens if not hundreds of PCEs. Has anyone scene this?

[thesteve]

i have not, not even on SNES with dead 7805
per the internals it looks like it could happen, but if you're concerned about it drop a zener across the output to short in case of overvoltage

[NightWolve]

i have not, not even on SNES with dead 7805
per the internals it looks like it could happen, but if you're concerned about it drop a zener across the output to short in case of overvoltage

Normally, with what he's referring to (and what happened to my SNES), the fuse saves the day anyway when the 7805 goes bad, no ? It's just that somebody not correctly guessing why the fuse burned, puts another one in, only to see it burn again but keeps going before diagnosing the real problem that leads to damage.

Does the NES not have an internal fuse ??

[wilykat]

http://www.freeinfosociety.com/electronics/schemview.php?id=2405

schematic shows no fuse. So when that 7805 fails, it will cook NES and turn it into blob of melted plastic and silicon.

In all of my time, I have had only one failed 7805 in a Commodore disk drive, it had burned open and not providing anything.  Out of maybe 1,000 7800 series and similar regulators I've checked.  I did have to replace a few in Atari 2600 because it was giving low voltage with original 30-year old regulators.  I have not had one short out or blow fuse.

Atari Lynx didn't use such regulator, they used a transistor and 5.7v zener diode in emitter-follower design. When either of those fails, there is nothing to prevent 9v from getting dumped into the entire system.  5v mod (originally on German site, English writeup on Atariage forum) fixes this with a real regulator or a 7805-compatible switching regulator chip.  All of my Lynxes uses the 5v mod.

Still it'd be good to check anyway.

[NightWolve]

http://www.freeinfosociety.com/electronics/schemview.php?id=2405
schematic shows no fuse. So when that 7805 fails, it will cook NES and turn it into blob of melted plastic and silicon.

Huh, that's bad. Would be a good thing for NES owners to mod a fuse slot in appropriately then. Or do a 5V mod with a modern, regulated power supply. The issue with that though is you may get strange behavior in the system, as I have observed when I did the 5V mod to my SNES. Weird background artifacts at times and what not, minor stuff, but it doesn't work exactly the same if you remove the 5V regulator and directly bring in a clean 5V USB-style power supply to that motherboard location. Guess you'd have to be as experienced as Steve to figure out why...