RetroKrazy

As the title says, I need a new membrane keyboard for my 400 if anyone has a working one just lying around... I'm based in the UK.

Well, after a LOT of checking, re-checking and checking again, one tiny bit of feedback started me thinking and led me to the solution. Or rather, showed me what an idiot I'd been. I'm so used to DC voltages that I never thought to ensure the -ve lead was on after the bridge recifier... So bring on the jibes, jokes, slagging and insults So I used a 10 ohm, 10W resistor pushed through either the 5a or 5b header and fixed the other end to ground (yeah, DC ground before anyone says ). This provided enough 'load' to test the 5v rails and mine show rock solid at 4.98v now. -5v and 12v show correctly without any load resistor. Thanks to all who helped out and look at it this way, with the diodes, caps and power regulators all done, this should be great for decades to come!

Will retest when back from holiday at various points on the board in case the points I chose were referenced to AC voltage however shouldn't be. And while I agree that the original caps could still be good, I am unwilling to risk a system for the sake of spending a bit on new ones.

Recapped as electrolitics are over 40 years old. Was not powered up to test prior so no previous voltage readings. -ve electrode on ground plane and +ve on each header.

Cheers, will order some and try that. On holiday ATM so will be when I'm back.

I recently purchased an Atari 400 (PAL model) and recapped the power board however, the voltages when tested are all over the place. I was wondering if anyone had any experience diagnosing these power boards? All electroltic caps have been replaced Vishay/Nichicon equivilants and polarity quadruple checked. Replaced CR201 Replaced CR202/CR203 Replaced 7805 (twice) and even tried with a Traco Power which made the measured voltage worse! Replaced 7812 (twice) Current Voltages Output at 7805 is 6v, not 5v Output at 7812 is 3.9v not 12v -5v reads as -12v on header GND reads as -7v on header Voltage at Bridge Rectifier is just over 7v DC Input voltage is 12vAC (well within operating specs of the 78xx chips) The board is being tested with no load and the RF Modulator unplugged (PAL Spec - it lifts out) as I was unwilling to plug it into the mainboard until the power board was sorted. S202 is being held down for testing however the -7v at ground is bothering me. If ground were correct, then the -5v and +12v would read correct and the 6v at 5a and 5b could be attributed to having no load. Any assistance would be appreciated.