PCEngineFans.com - The PC Engine and TurboGrafx-16 Community Forum
NEC TG-16/TE/TurboDuo => TG/PCE Repair/Mod Discussion => Topic started by: schweaty on January 07, 2014, 06:46:29 AM
-
Alright, I know this is a PCE/TG16 repair thread, but I can't seem to find the info I'm looking for elsewhere and there are some very knowledgeable folks on this forum. It seems like the general concepts are the same, so I will offer it up here.
So, I have a non-functioning SNES-101. It will not power up. The power adapter works; it puts out the right voltage on the multimeter. The fuse checks good on the continuity test. The jack also shows continuity on the multimeter.
Here's where it gets interesting: the voltage regulator is only showing 4V on the input and 2.3V on the output. Its a 5V 7805 regulator, so it needs at least around 6.5V or so to work. I'm willing to get a new regulator (its only about $2) but I don't think that will fix it. It seems like there is a low-voltage issue somewhere. I might re-solder the jack to the pcb and replace the voltage regulator if that doesnt work.
The guy I bought it from says it quit working after an electrical storm. Anyone have any ideas? Is it a prime candidate to be gutted and turn into an emulator box? Is there someplace else I should take this question to? Any input is appreciated.
-
Hmm, I had a similar issue. That +5V regulator burned out. Instead of buying a new one, I desoldered it off and I did a +5V power mod. I got a good, well-regulated +5V power supply, soldered the original tip from the old power supply on to it, and on the motherboard, I had to perform a bypass. Nice thing is I could get rid of that big heat sink and so the system runs with less heat internally (it's all at the power supply, that has such regulators inside).
So, that's what I did. Works. But for you, yeah, easiest to try replacing it. It could be the cause of the voltage drop having shorted or something. If not, there is a short somewhere else.
Here's a good link to a store for it:
http://console5.com/store/7805-5-volt-regulator.html
.50 cents
Desolder it off first, and then test the incoming voltage, see if it's 10-12V after that. If so, then you know it was causing the short and hence voltage drop.
-
Thanks for the input Nightwolve! I will give it a shot.
-
A failing 7805 can give falling voltage on the in, it's partly shorted internally on the input, when that's happening it drains the input and of coarse can't output the voltage correctly.
A unregulated AC adapter can get very hot when this happens and burn, even a regulated one can as it's like having a never ending eating load.
-
A failing 7805 can give falling voltage on the in, it's partly shorted internally on the input, when that's happening it drains the input and of coarse can't output the voltage correctly.
This was my initial thought but I couldn't substantiate it anywhere on the interwebs. Thanks Fidde_se, this was just the type of insight I only find here.
-
I don't know if it's possible, but could a blown fuse still supply enough Voltage to be ready by a continuity? I know the fuses go a lot on SNES's, and it's a top problem. If you have an extra one, I'd switch just to check that it's not supplying irregular Voltage.
-
I kind of got away from this project a little while ago and dug back in today. I need to vent my frustration a little. I replaced the voltage regulator and desoldered/resoldered the jack outlet to the PCB. Still getting the exact same low voltage readings at the voltage regulator. I might try and heat the PCB as a last ditch effort to reflow the board. I'm pretty much out of ideas. I think it might be a lost cause.
-
You have a short on the board
It could be before or after the regulator
If low voltage before regulator and no heat at the reg short is before
If reg hot, short is in or after reg
Reflow won't help
Sent from my ADR6300 using Tapatalk 2
-
thanks, steve. no heat on the reg. there is what i think is a common mode inductor/choke next to the fuse that looks like it leads from the jack to the reg. could that have gone bad? is there a way to test it?
-
Only way to test an inductor is to isolate it and test the impedance. Unless you know the proper value, thats not going to help you. Now if its a dead short or open circuit in the inductor then thats an obvious issue. Now to test the actual mH value your going to need an inductance meter.
Like Steve pointed out, since the reg is not overheating, that leads you to believe the upstream circuit is shorted (including the power supply). You say you tested the AC adapter for proper output voltage but since your testing with no load, you can't rule that ac adapter out just yet. It is possible for the internal transformer of the ac adapter to work until you place a load on it. Do you know someone with another console you can try the ac adapter on? Another option would be to build a small load bank to hook up to the AC adapter. 12V filiment lightbulbs work good for this. Simple series circuit in the light fixtures would be the way to go. We do this same method for testing network transformers in the 120-480V secondary grid of chicago. (I work for the power company)
You can still have a short on the PCB as well.
-
I don't see any meaning in repairing a snes?
-
I don't see any meaning in repairing a snes?
Pfft.
Anyway, I would totally suggest trying another PSU as it wouldn't hurt. Failing that, there is the possibility that one of the chips has failed and is causing the undervoltage issue.
-
I'd suspect a shorted cap between the supply and regulator, as it was lightning related
-
not sure why i didnt check this before, but when i check the voltage where the jack is soldered to the PCB im getting the same low voltage as the reg input (4.3V) under load. its also a pretty inconsistent reading (i have to hold the probe on it just right). unfortunately, where you plug in the ac adapter is encased in the plastic of the back panel, so i cant take it apart to check it out. or the problem might be like tggodfrey said and the adapter might be a dud under load. its a real cheap third party sega/snes combo power adapter.
-
its a real cheap third party sega/snes combo power adapter.
Those are some of the worst PSUs ever made, dump it and see if you can get ahold of an actual Nintendo AC adapter.
-
Is it low when power switch is off?
-
steve, you must be a goddamn genius. No, the voltage is fine while the switch is off (9V+). As soon as you turn on the switch, it goes down to 4V. This indicates a shit ac adaptor, yes?
-
No it means the short is after the switch, before the regulator
-
why do i feel like the kid playing Chutes and Ladders who hits the last chute right before the finish line
-
lol, IDK
-
im not 100% what parts are between reg and switch
if you lift the input pin of the reg and jumper the + input from the jack it will isolate it
alternately if you remove the reg and turn power on it shouldnt pull the voltage down
trying another supply first is best
if supply doesnt get hot when outputting 4V its likely a bad supply