Nintendo M82 - RF box

Hello members of assemblergames

I recently got a Nintendo M82 in for repair. One of the problems was that the RF box had some issues.

Nintendo M82 RF box


Nintendo 8 Bit RF box


So i was thinking, that RF box looks familiar. It is the "same" as the NES. Well so i thought..... I desoldered and rebuild the NES rf box put everyting back together. Powered it on, but there is no sound. Either RF or composite got sound. On the component side they are identical, but maybe the bottom (SMD) side got something redesigned? I never checked that. However the numbers on the side doesnt match.

Luckily i could save the old one by redesign / repair the pcb. But any one else tried to do this?

(CPU and PPU however is interchangeable)

 

I would suggest looking at the motherboard itself. In my experience, most audio problems originate from there as opposed to the RF/AV box. Also, by "rebuilding" do you mean you replaced all of the components? If you haven't replaced any of the caps inside that box, I'd do that before turning your attention to the motherboard.

 

The RF box from the NES worked before i putted it in the M82. By "rebuilding" i was removing the 7805 and used the jumper from the M82 RF box. Then i repaired the original M82 rf box, putted it back and bam sound.

 

Yes, but if no sound is going into the RF box then you are not going to magically get sound coming out. Sound comes from Pins 1 and 2 of the CPU, goes through a couple of resistors before going into pin 10 of the 74HCU04 (it coud be different pins on the M82 but I doubt it, however a visual trace should tell you) which amplifies the sound, it comes out of pin 11. It is likely that this is dead if the NES is working. It is quite simple to test if you are getting audio from any part of it. Make sure if you replace the 74HCU04 that you replace it with a HCU chip and not a HC or HCT chip otherwise you won't get audio.

 

Does a Nintendo M82 got a 74HCU04?

 

Open it up and check it out, assuming it's still with you.

 

No sorry it is back to the owner.

 

Last time I didn't get sound out of an RF unit like those two it was because of bad caps. There was sound but I had to really crank my amp to eardrum blowing levels before I heard anything.

While I realize everyone is foaming at the mouth over capacitors being the problem for everything when it comes to sound and the box producing the sound is upwards of 20 years old it is usually the case. Worst case you replaced some capacitors that now won't need replacing for at least a decade.

 

The M82 does have a 74HCU04, it is used for other things apart from being a amplifier. There are a few caps between the CPU, 74HCU04 and the RF but nothing that would stop the sound from working.

 

It does look similar to the NES RF box, in which case, it might be possible to just use a few parts to change the RF output to composite instead; like I did for the NES: http://www.made-by-bacteria.com/forum/viewtopic.php?f=29&t=232

Just a thought.

The Nintendo M82 would logically probably have the same internals as a normal NES.

Pic I Googled for one of them:

 

it's possible to set it for unlimited time of play?

 

Mine didn't stop working as a whole either; it just wasn't getting amplified properly before hitting the connector.