Nintendo NES (toaster), blinking red light and no audio fix

[CapLeaker]

I've got that old Nintendo NES on my bench. Had some real issues that old toaster box. First, it would always reset. So we played with the 72 pin header and replaced it with a working one and no joy. The old header did have an corrosion issue so we boiled it in hot water and now it never misses a beat.
Anyway... knowing the problem wasn't really the header, we clipped the pin 4 on U10 the CIC chip. That fixed the blinking led and reset problem. Nintendo!
However we had no audio on RF or RCA. So I replaced C25 (16V 100uf) in the alps tuner box (had 450 Ohms ESR!), right behind the 7805 regulator. After trying to isolate the audio issue, I came to find out that the problem was the 74HCU04 (hex inverter) on the main board. Replaced C23 (50V 1uF) on the main board (before you do this step, read next sentence!). Lifted the leg of inductor FC1 and installed C23 only with the negative leg soldered to the main board. The positive leg is bent up with a piece of wire soldered to it to reach FC1 (see pic). To power the 2sc1740 in the rf box, I took the bad output of the 74HCU04 (it still had 5V in my case), where I unsoldered one side of FC1, soldered a (blue) resistor, roughly 450k Ohm (something I could put my hand on quick), with the 2nd leg soldered to the inductor and wire. Basically I bypassed one audio amplifier stage (pin 10 and 11 of the 74HCU04.
This mod will restore the audio without replacing U9, if it is bad. However the audio will be a little lower than original, since we bypass an amplifier stage, but there will be still enough audio gain for the TV. The beauty is for the guys that still use the RF port, the audio will be there too!

There isn't much to be found on the internet about this issue when U9 goes FUBAR. Of course there are other audio hacks on the net, but this is my version of it, trying not to modify too much and still have an original looking and working NES.

[kaboom]

Re: Nintendo NES (toaster), blinking red light and no audio fix

74(H,HC,HCT)04 is a hex inverter.

Why not replace it? Cut the leads, freeing the IC, then heat and pull the stubs from the board. Clean the holes with solder wick.

Hope you replaced all the electros in there...

Fix it right or go home.

[stj]

Re: Nintendo NES (toaster), blinking red light and no audio fix

yea, poor bodge.
you should do a full recap and replace failed parts.

[Agent24]

Re: Nintendo NES (toaster), blinking red light and no audio fix

That's an old board, no big planes etc, even PTH should be easy as there. Cut the pins off at the IC body with a sharp blade and remove one by one. Wick will clear the holes. If you got a desoldering gun you don't even need to think.

[CapLeaker]

Re: Nintendo NES (toaster), blinking red light and no audio fix

74(H,HC,HCT)04 is a hex inverter.

Why not replace it? Cut the leads, freeing the IC, then heat and pull the stubs from the board. Clean the holes with solder wick.

Hope you replaced all the electros in there...

Fix it right or go home.

I could, kids wanted to play. Try waiting for a month for parts.

yea, poor bodge.
you should do a full recap and replace failed parts.

Reading a few of your posts, it seems like a standard thing of your answers. The ones that figured out that I can easily reverse my mod and fix it right were kaboom and Agent24. For the caps, I don't need to take the lazy shotgutgun approach, as I do have proper testing tools. Another sign you didn't read my post right, you could have seen that I measured 450ohm ESR on one. This buys me easy time to wait for parts and Kids can play. I just can't run downtown and buy whatever.

That's an old board, no big planes etc, even PTH should be easy as there. Cut the pins off at the IC body with a sharp blade and remove one by one. Wick will clear the holes. If you got a desoldering gun you don't even need to think.

That mod is the reason without botching (like stj accused me of) things up. Unit works like it did before, besides the region free mod. get out my hot air desoldering station and replace the 74HC04 when I order next time. Saves me 20$ shipping for a 1$ part. No parts lost, just easy as to solder them back in place. Done.

[Agent24]

Re: Nintendo NES (toaster), blinking red light and no audio fix

That mod is the reason without botching (like stj accused me of) things up. Unit works like it did before, besides the region free mod. get out my hot air desoldering station and replace the 74HC04 when I order next time. Saves me 20$ shipping for a 1$ part. No parts lost, just easy as to solder them back in place. Done.

Heads up just in case, A 74HC04 is not the same as the 74HCU04 your unit uses. You need the 74HCU04 because it's working with analog signals.

[CapLeaker]

Re: Nintendo NES (toaster), blinking red light and no audio fix

It should read HCU, sorry... I had it correctly in my first post. Thanks for pointing out that typo

[kc8adu]

Re: Nintendo NES (toaster), blinking red light and no audio fix

lots of ring cracked joints in that pic.and that brown cap looks like it leaked.
it was s.o.p to snip the cic when open for any service.
i changed thousands of 72 pin connectors.
even had blindfold contests.

[CapLeaker]

Re: Nintendo NES (toaster), blinking red light and no audio fix

Cap is brand new Nichicon PW series no worries there. I am not sure why, but ring cracks always look worse in a picture. I have gone over it, but it got late the day I posted this. Before posting this thread, it hat struck me a bit flat in face was, with all them original NES's out there, that there is nothing much to find about the symptoms our NES had. It's usually always the same goose chase, then the thread goes unsolved and abandoned.
The goal was to get it back working in a simple order without modifying the crap out of it until I make another parts order.

[artois7]

Re: Nintendo NES (toaster), blinking red light and no audio fix

An effective little workaround; nothing more, nothing less. Not sure what the problem is!

Good job mate.

[kaboom]

Re: Nintendo NES (toaster), blinking red light and no audio fix

with all them original NES's out there, that there is nothing much to find about the symptoms our NES had. It's usually always the same goose chase, then the thread goes unsolved and abandoned.

I've noticed the same, not with just the NES, but also the SNES and N64.

I got a $5 N64 off ebay. Seemed to have some activity, like video sync, but never actually ran any games.

I scoped all signal pins of the CPU and RDP, all activity stopped after about two seconds. Each data line, obviously, had a different pattern. So I checked around the RAM. All but one signal line looked ok. That last one didn't look right- sort of fuzzy and not having distinct HIs or LOWs. Could it just have been an open termination/load resistor? I took a 68 ohm resistor and held it between the suspect line and VTerm. The unit worked!

It was easy to repair the open trace. Those chips can be "folded over" by unsoldering four "anchor pins," two on each end, on the blank side of the chips.

Unsoldered those, flipped the chip up, and made the repair underneath. Soldered it back down, and all was well.

Pretty good for five bucks.

Here's what look like reverse engineered schematics for the NES. I won't post them inline, since they're rather large. Beware of some "obvious" omissions, not the least of which is an ungrounded 7805!

[CapLeaker]

Re: Nintendo NES (toaster), blinking red light and no audio fix

Oh! Thanks for posting the schematics for the NES. Well... Wouldn't you suppose, I've got something else in for repair, so I've ordered a couple of 74hcu04. Should have them end of next week.
O.k. On the N64 and yes... Things can act funny quick (like the autocorrect on my iPad). So what would have caused the line under the Ram to go bad? A leaking cap? I have seen this on some HAM gear. Cap gets bad, radio acts up, radio gets repaired. Someone then got lazy, didn't clean up the mess underneath the filters, a year later and the radio is back on the bench. I have repaired tons of them old 1200 to 9600 baud TNC's. Most of them were lightning strike specials, but I got every single one working. I just like that area of electronics and like to keep it alive.

[CapLeaker]

Re: Nintendo NES (toaster), blinking red light and no audio fix

So to finish up the thread, the other day I got the 74hcu04. Swapped the old for the new IC, removed my simple mod and the NES is working fine as kind!

I did measure the old IC and 2 of the inverters were bad. One on the top and to other one on the bottom row.

Btw. Once the 74hcu04 is removed the unit won't turn on either.

Hope this helps.

[kaboom]

Re: Nintendo NES (toaster), blinking red light and no audio fix

So what would have caused the line under the Ram to go bad? A leaking cap?

It was either got rained on, or soda(?) was spilled into it.

I have seen this on some HAM gear. Cap gets bad, radio acts up, radio gets repaired. Someone then got lazy, didn't clean up the mess underneath the filters, a year later and the radio is back on the bench.

Like those Panasonic VCR power supplies? The AG1950/60/70s (and others) always got bad caps in their power supplies. Many blew up when powered on for "testing"- electrolyte on the board is bad news with power applied.

So to finish up the thread, the other day I got the 74hcu04. Swapped the old for the new IC, removed my simple mod and the NES is working fine as kind!

Good to hear it!

I did measure the old IC and 2 of the inverters were bad. One on the top and to other one on the bottom row.

Btw. Once the 74hcu04 is removed the unit won't turn on either.

Hope this helps.

One section inverts and passes the VRAM reset, but the others are involved with the CIC and its clock. Which explains the flashing screen and cycling reset.

I wonder how many CIC mods were performed when it was really a bad hex inverter? Interesting...

Don't break any controllers!

[CapLeaker]

Re: Nintendo NES (toaster), blinking red light and no audio fix

One section inverts and passes the VRAM reset, but the others are involved with the CIC and its clock. Which explains the flashing screen and cycling reset.

I wonder how many CIC mods were performed when it was really a bad hex inverter? Interesting...

Don't break any controllers!

To satisfy your curiosity, we both now on the top row, 2 pins (10 and 11)on the inverter was used for audio amplification. The other bad inverter was on (pin 3 and 4) the bottom row of the IC and that is between the CIC and pin 71 on the header. It is just funny that pin 12 and 13 didn't blow on the 74hcu04.

Anyway... I try not to break any controllers.

The second thing I am wondering is too, how many people couldn't figure out the audio or CIC problem and threw the NES into the bin for a 75 cent part.

[stj]

Re: Nintendo NES (toaster), blinking red light and no audio fix

most people couldnt even get into nintendo stuff because of the whitworh-head security screws they liked to use.