Re: 7104 Power Supply Dummy Load


On Wed, Jan 9, 2019 at 04:52 AM, george edmonds wrote:

My load draws 32 watts and Goran suggested I needed to apply at least a 50
watt load.
(actually Dennis wrote, but that is how it got quoted)

Actually that seems close enough, but there is nothing wrong with putting another resistor there to up it to 50 watts.

My take on it is the main source you need to load is the 108. That is the one it senses. The -17 at the other end it not sensed as it is Zenered down to -9. Whyever they did that, thermal comp or whatever, really doesn't matter.

Loading the other sources is only necessary so that the little spikes or whatever that didn't get snubbed at the primary of T1230 don't get rectified and run the voltage up to the point the filters pop. There shouldn't be much with that type of supply but better safe than sorry.

You didn't mention loading the 108, and the question exists - what were they doing when they were in the scopes ? Is it the same ?

I do agree that since they are all doing the same thing the problem could be your dummy load, and my best guess it that the 108 must be loaded.

Another quick check you might try is to actually short something and see if it starts ticking. The 108 would seem the likely candidate but to avoid stressing its bridge you can use the output that would have gone to the HV rectifiers etc. If it ticks then, that is a valuable piece of information.

I just got the print a few minutes ago so I am not sure exactly how it detects overcurrent, but if that is oversensitive they could tick when in a scope but another supply will work. I haven't looked yet because if you short it and it doesn't tick it would be a moot point.

Good luck, those power supplies are "fun" ones. I see Tekwiki is wrong though, what it says about them applies to the linear (non switching iron) power supply, not the SMPS.

Someone correct me if I'm wrong.

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