PCEngineFans.com - The PC Engine and TurboGrafx-16 Community Forum
NEC TG-16/TE/TurboDuo => TG/PCE Repair/Mod Discussion => Topic started by: nat on June 12, 2008, 02:49:20 PM
-
Here's a new one.
Today during a game of Rayxanber II my Duo started emitting a quiet, steady white noise static-y sound. This noise is not audible when music is playing-- there are no audio glitches or anything (I had already replaced all the caps in the audio circuit a few months ago). You can only hear the sound when the music is quiet or nonexistent-- for example, between levels, when boss fights are loading, etc. The sound is present whether I'm playing a game or not. For example, if I simply turn the system on with no game inserted the static is present even at the BIOS screen. The white noise is present over the headphones as well.
What I ruled out:
1) A/V cable. Tried two (first party NEC) A/V cables with the same result, not to mention the sound is present over the headphones too.
2) My TV. Tried multiple other systems using the same input jacks on my TV, no problems.
3) Caps. I spent 3 hours replacing every f*cking capacitor on the logic board. The noise is still there.
4) A/V port. As if hearing the sound over the headphones wasn't good enough to rule out the A/V port, I resoldered the A/V port anyway.
Uhh... I think that's about it. What else does that leave? I've never heard of such a problem. All previous accounts of "static-y audio" have to do with redbook CD audio. This sound is present whenever the system is powered on at all, regardless of whether a game is playing or not.
The next step for me is to run the logic board through the dishwasher.
-
It does it during hu-card play also? Oddly at random times I have had this happen to me with a few hu-cards only, at random times (3 or 4 times maybe in my life) on the Coregrafx I had and the current Supergrafx. Very rare,and it occurred during game play,ect...just a constant flow of noise that bugs the shit out of me,less during gameplay as the normal audio mostly drowned it out. After I would remove the hucard and try a different one the audio was fine,and re-insert the original one and the issue would be there again or non existent (seemed to be determined by how long I left the hu-card out of the system).
Happened to me on Rabio Lepus,and I don't remember what else. Has not happened in forever though. Good luck figuring your problem out.
-
Yeah it happens during HuCard play too, or no play at all (like I said, even on the BIOS system card screen with nothing in the console).
I will surely update this space if I figure it out.
-
Giving it the old DW bath sounds like a good course of action. That could help get rid of any weird phantom problems: dirt, grime, any possibility of loose solder rolling around making contact, things stuck to the board, etc.
The sound can be heard from the speakers and in the headphones, but not internally from within the system, correct?
You replaced all the caps, or just all the electrolytic ones? Think it could be one of those damn SMD caps? I've never heard of issues with them, but who knows...
If it was an internal noise I'd say:
- Check everything power related. I once had some CMVS issues with PSU wiring that made the system emit a quiet "whining" noise.
- Check the laser. Swap lasers with another Duo and test both for any changes. Play around with the silver pots.
-
Yeah, it's a speaker noise, not a noise from the system itself.
No, I didn't replace those SMD caps. I can't imagine it would be those... I mean, no one has EVER had a problem with them, right?
-
Not that I am aware of Nat.
-
I've never heard of anyone having issues with them, but has anyone ever looked into what they actually control? It's been a while since I've opened a Duo, but from what I recall there were enough of them there to think about. Wouldn't it be possible that some of them relate to the audio (whether or not it's the culprit causing the problem here)? I'd love to see a SMD chart...
-
Sounds strongly like interference, honestly. Either that or an overload to one of the audio circuits; that could be caused by a shorted resistor or failing voltage regulator.
-
Probably nothing shorted since it started at a time when my Duo hadn't been open in months.
Anyone have any information on the voltage regulators on these things? That's a bit beyond my field of expertise.
-
the problem is "fixed."
A couple of runs through the dishwasher and a long soapy soak did the logic board good.
I'm going to write this one up as a case of old crusty caps leaking electrolytics all over the board and causing random shorts. Since I replaced all the caps anyway in an attempt to correct the problem, there will be no more leakage and the problem shouldn't return at all (unless for some reason that wasn't the real issue).
-
What kind of soap did you use? I know water won't harm unpowered electronics, but I would think that soap could damage traces.
-
http://www.seventhgeneration.com/Dishwashing-Soap
-
Way to go Nat. Glad to hear it's fixed. What all did you run in the dishwasher? How far did you strip down the board? I didn't know you could wash pcb's.
-
I didn't know you could wash pcb's.
Absolutely. It was a trick I learned when I used to repair Apple Macintosh computers of the same vintage as the Duo. They suffered from problems caused by the same batch of bad caps that were prevalent in electronics of the period (including the NEC console line). We'd replace the caps and run the logic boards through the dishwasher to remove any rogue electrolytic. PCBs undergo a "bath" very similar to a dishwasher cycle as part of the manufacturing process, actually.
Way to go Nat. Glad to hear it's fixed. What all did you run in the dishwasher? How far did you strip down the board?
I ran the logic board itself. Which is to say, the only circuit board inside the Duo. It's unnecessary to strip it down at all. Just unplug the optical assembly (you don't want to wash the laser, haha) and the power supply mains and drop the PCB on the bottom rack in the dishwasher. Run a normal cycle using a gentle detergent. Let it air dry (24 hours or longer).
Oh, and you'll want to back up your BRAM with a Ten No Koe if you ever do this. Giving it the bath wiped all my save files. Luckily I did a backup not too long ago.
-
Nat,
did you use dishwashing soap or dishwashing detergent? The soap says "not for use in dishwasher" on it:
(http://www.seventhgeneration.com/files/images/products/large/prod_dish-liquid_25oz-lfm_260x282.jpg)
Let me know, I picked up both from the store today because it is actually a good product to have if you have kids in the house.
-
Nat - well I removed the large caps around the pre and post amp area. I found that I had left some residue (it wasn't really noticeable but it was there). I really cleaned it up good with alcohol and swabs (diluted alcohol with water) and cleaned up very nicely. I was debating a dishwash since I found a problem area. Maybe I should solder th caps back and then test the unit again before dishwash. Of course if I have th caps off it might be a good time to do that.
UPDATE: The Duo is running on normal cycle right now.......
-
Is dishwashing the board necessary? When I changed the caps in the op amp section I scrubbed the pads with a q-tip soaked in alcohol. I also had to change the caps located in the front right corner to get the laser to read properly. Maybe I will change them all and give this a shot if I ever get it to work again. :cry:
-
what is wrong with yours Ogre. Since the static audio was really bugging me (and I replaced almost every cap) for me it was necessary. Of course I wouldn't have done it if I didn't have a Duo-R on the way from the land of the rising sun.
-
The problem with my Duo is the fact that it no longer powers on. The Voltage travels to the point of the diode right next to the main fuse but not after. I think the diode is at fault , but i have not had the time lately to probe further. So for now I am using a Duo R I purchased from the seller on Ebay thats premodded RGB. :dance:
-
Hey I bought from the same seller I think. Was it Doujindance? Let me know your thoughts on the Duo-R. I am waiting for mine to arrive.
You know I would post up your Diode question on the Gamesx.com forums (mod and repair) and see if Lawrence can answer that one. He had a schematic once I believe.
The problem with my Duo is the fact that it no longer powers on. The Voltage travels to the point of the diode right next to the main fuse but not after. I think the diode is at fault , but i have not had the time lately to probe further. So for now I am using a Duo R I purchased from the seller on Ebay thats premodded RGB. :dance:
-
Nat - need your help here. Did 2 soap cycles, then 1 cycle just water. Dried really well with fans, and let sit for 5 days. There is no sound now. I let it sit on for about 1 hour. I can turn the volume way up and hear very faint video game audio, but it is very quite. Please let me know your thoughts...
UPDATE - so I checked out some caps, I replaced one that was a little suspicous, and re-flashed the caps on the bottom of the board (just held the solder iron melted solder and then let cool). Slapped it back together and full sound...no static!
Also - for some reason I didn't lose my saves even with 3 cycles.
-
Great, I'm glad to hear it. Another Duo saved! Should be good for years to come.
-
Nat - thanks for replying back. Ok this is whats wierd, the sound periodically goes out seams like every few times I power it on. Should I start replacing some caps again in the sound area? When the sound is out if I turn the volume all the way up, I can barerly hear it. It never comes back on when it powers on like that. However, turn it off, wait a while, back on and it is good. Very strange. Right now it is ok. Suggestions? I replaced EVERY cap except for the 3.3uf cap, and 2 other caps around that area. Very strange (I think this Duo doesn't like me).
-
You know, that's interesting, and I actually had a case where I repaired a Duo for someone and after I sent it back they reported something similar. Because of the individual in question, I thought they were full of shit to be perfectly frank, but after hearing your story maybe they were telling the truth. It's odd because I tested that person's Duo for like 3 hours straight on two different occasions and it had no audio problems at all during that period of time. Before that instance, and now yours, I have never otherwise heard of such a phenomenon. I would replace any caps you haven't already replaced, but it seems doubtful the ones in the area you specified have any tie to the audio system. But the bottom line is, if the issue persists, there is a cap somewhere that is acting up. If you've replaced them all, it means one of the replacements is bad, was damaged on installation, or was installed incorrectly. You might try reflowing the solder on all the replaced caps in case it's a bad solder job making a shoddy connection somewhere. Sometimes the problem isn't visible and you just have to give in and do it all over again.
-
yeah most of the time it is fine. The static issue definitaly is gone. Note - before I dishwashed, I used rubbing alcohol and removed all visible goo from the old caps, and the static was still present. So one problem fixed, but another underlying problem is present. I suspect a bad cap somewhere...
-
Nat - it has been fine the last few times I have powered the unit. The thing I am noticing is the volume seams to be lower, maybe about 25-30% lower than normal. I have to really turn up the sound, my Duo-R is much louder at the same volume level. Does this point to a suspicious cap in the amp area?