famicomaster2

Dang. How costly are they on eBay? Would I be able to find them cheaply somewhere else? Would it be possible to convert an AT / ATX power supply to give the -5v rail like I need? I read elsewhere that older supplies have this, but the oldest supply I currently have is an AT class unit for 130W in a Pentium machine, which I have been using as a serial terminal in some projects. I was indeed measuring from +5 to -5, but I've gone back and measured everything again. To correct: "Good" supply: +5v - GND : 5 volts GND - -5v : 5 volts +12v - GND: 11 volts 78M05 : 5 volts "Bad" supply : +5v - GND : 5 volts GND - -5v : 10 volts +12v - GND: 10 volts 78M05 : 11 volts Transformer : 18v (1,2) : 18 volts 8.5v (2,4): 8 volts I read in another thread that the only things using the -5 volt rail are the VDP and GROMs, if this is true I'm less worried about the machines but still quite worried. Could this spike have ruined them? The VDP is not much of a worry since I wanted an F18A anyways, but what of the GROMs? I know that you can tell if they're okay by the startup tone, but my video cable is odd (standard RCA composite on one end and 3.5mm jack on the other) and I don't seem to get any sound out of the machines. If they've gone bad, how would I get a replacement? I read somewhere that you can emulate them with an Arduino, and I have at least 5 of those lying around (Unos and a Mega), but I've no way to confirm this. Ideas? Questions? I can test just about anything on these supplies should the information be needed, so long as I have the tools. I might have mentioned before but my Oscillograph is currently awaiting new sweep tubes, so for the time being I can't get any waveforms.

Update: I checked the voltage outputs and found something interesting: On the good power supply, we get a near perfect 12v across +12v and GND, and about 3.5v across the LED. However, across +5v and -5v we seem to be getting nearly *10 volts*. I checked the 78M05 regulator and got a perfect 5 volts - until it started wobbling and shot flames at me. It no longer gives any voltage now. The fault was probably somewhere else in the circuit, since the regulator seemed to be okay before it killed itself. After the 78M05 blew, we get nothing across either rail - both 0 volts. I checked the transformer and it is perfectly on the dot - it was definitely on the DC side. My main question now is whether or not the machines will work anymore. Should I attach them to a modern PC supply, since they have +5, +12, -5, and GND rails? Would that be safe to test the machines with? EDIT1: The 78M05 is back? It shot a lot of sparks last time, but it's giving me 5 volts again, but the output of the supply is still 10v and 11.8v. Could I simply replace the capacitors or is there something bigger happening here? EDIT2: Attached a 12v PC fan to the 12 volt rail and it ran with no problems. Put it on the 5 volt rail expecting it to be at a similar speed but it dropped severely after a few seconds and fluctuated quite a bit as if there was a lot of noise in the output. My oscilloscope is currently dead (sweep tubes got water damaged), so I can't really check for this at the moment. Measured across the 5 volt rail with the fan attached and it seemed to be at around 5 volts - it might just be some open circuit voltage, but I don't really know how to tell. Maybe the fan is just asking too much of the supply (12v .13A)? I've got no capacitor tester right now, otherwise I'd check the electrolytics. EDIT3: I checked the bad supply - the 12 volt rail is a little low at 10 volts and the 5 volt rail is giving me nearly 20 volts open circuit! The regulator is giving out 10v on this one so it's definitely bad, but could any part of this computer have survived this? Closed circuit it's far less than 5 volts - about 3.7 volts or so with the fan attached. I should stop testing these, they're making me less and less hopeful of the computer's survival.

The old red LED was very dim anyways - it was on its way out (you couldn't see it unless the room was very dark). I replaced (I believe) R2, the resistor immediately attached to the LED's anode. It was a 5% tolerance resistor, 2.2KΩ, if I recall. The measurement was taken with a cheap analog multimeter like i said, so it was probably off by a bit. The power supply seemed to work when I had it in the first TI, only the LED would occasionally flash. I figured this was a bad connection since my soldering job was less than worthy, I was out of desoldering wick so I clipped the parts off and soldered onto the stubs. Not the best way to do it, but it got the job done (I think). How much would you want for the extra supply? I'm not even sure if the mainboards work anymore, really hoping against all odds that they had some kind of protection on them at this point... It's not like the supplies weren't working before - both machines worked (the second, boxed one had some keyboard problems but that's inconsequential, I think) until now.

I have 2 different TI 99/4A systems (one with the solid state badge and one without), and both of them were working fine earlier today. However, when I came home the power LED had failed on one unit. I opened the machine up and replaced the LED with a blue one - but it didn't light. I replaced the resistor with a 4.7kΩ resistor and it was fine. However, before replacing the resistor, I used an analog multimeter to measure the voltage across the LED (8v, apparently), but one of the probes slipped into the middle of the supply and caused a few sparks to fly. However, the LED was still illuminated and it seemed to work fine. The computer was disconnected from the supply when this happened. However, when I reassembled the computer... Nothing. A few white dots come through the display on power up but that's it. I figure this was probably my fault and put a known good supply in - no luck. Naturally, being as stupid as I am and it being 11PM, I put the bad supply in the other machine. The same thing happened. I have not yet put the good one back in to test it. Did I just accidentally kill two different TI 99 machines? I really hope not, I love these things, one even has the packaging! Is there any way to fix these or even to diagnose what's wrong? I'd really like them to work but I don't want to go buy another machine, I just don't have the money.