NES power problem

One of the NES units I am fixing shuts off spontaneously after a few seconds. As it shuts itself off the sound video spaz out. After it shuts off the power light slowly dims and then goes out. It wont turn on again unless left for a few minutes with the power switch off. The unit has had the 10NES disabled, something I do with every NES repair. I am also uning a 1602 Genesis AC Adapter, I suspect the problem is in power/av unit inside the system. Can someone help me ID the failed component.

 

I'd start with the 7805 regulator. It's supposed to have a steady 5v output (pin 3)

 

I'll check that later, almost 2:30AM and still awake...

 

oh yeah have you tried a different power supply? If one is bad or something it can do what you described.

 

No I haven't but 2 other nes units work fine with it.

Edit: the voltage regulator is fine,
I was testing the power/av module with a multimeter and found that pin 5 has a standby voltage of 12.5v, the normal reading seems to be 11.89, so it is running over half a volt high. In a working unit that drops to 9.72 when the power switch is turned on but in the bad one it drops to 9.04 and continues falling. This continues until the voltage falls between 5v-6.5v volts after which it drops again to 3.52 at the moment of failure. I don't think this is a capacitor or voltage regulator problem, for the record the power unit in the failed unit is a Mitsumi module.

 

It is the bridge rectifier, the unit works great when using the ac adapter from an old scanner that had a similar rating but the opposite polarity compared to the 1602. Anyone know a good replacement for that?

 

AC doesnt have a polarity.

Are you sure its not just a broken PSU or dodgy power connector?

 

Yes I know that, the whole point of the bridge rectifier is to polarize the AC, ie convert it to pulsating DC. Running it under DC current revealed that one side of the rectifier had high leakage. Pulling a rectifier out of a working unit fixed it. Where can I acquire a replacement for this?

 

Well you said you got an AC adapter with the opposite polarity... if you knew that, then why say something completely counter to it?

And pretty much any should be fine, IIRC they are all pretty much the same size. I got a bunch from rs components, I am sure you can just do a search on mouser/digikey and compare the dimensions in the datasheet.

 

BECAUSE MOST AC ADAPTORS OUTPUT DC!!! During testing I used a 1602 Sega Genesis AC Adapter (DC9V center negative), the NES would shut off after less than 2 minutes, usually far sooner. I grab an AC Adapter for an old scanner, this one is DC9V center positive hence the OPPOSITE polarity. Again the 1602 is a known good, I fixed 5 out of 7 NES units I have been working on using this exact one. The only component that could fail this way is the bridge rectifier.

That is what I needed to know before I go to RadioShack to buy one.

 

Just a terminology difference I guess - I wouldn't call it an AC adapter. I know how polarity works, but I am not used to calling AC adapters...

If its outputting DC, then (at least from suppliers and my experience in the UK) its a power supply or a AC/DC Adapter. AC adapter just implies AC to me - hence the confusion.

e.g.
http://www.maplin.co.uk/batteries-and-power/power-supply-adaptors/fixed-voltage-power-supplies
http://www.maplin.co.uk/ac-dc-multi-voltage-power-supply-46107


Just a misunderstanding

 

I understand, sorry about getting frustrated. AC Adapter (or Adaptor) is the standard terminology here in the states, power supply around here implies a complex or high power device like a PC power supply though as mentioned sometimes the spelling can be a bit unpredictable.

 

Both spellings are fine, even over here in the UK!

Any decent component supplier would have a replacement - although I don't consider Radio Shack a decent component supplier these days! Take a look at my list of suppliers, it's a sticky.