09-10-2019, 08:32 AM
It's been in pieces on my office desk for a couple of weeks at least. Pressures of work means that progress has been disappointingly slow. This power supply is unusually complex, and not all of my initial assumptions were correct. I'm still not sure I know what the TL594 is actually doing. I have to return the PSU in working condition at some point, but if the supply wasn't needed, I would desolder the daughter boards and reverse-engineer them more thoroughly, but as it is, it's really quite hard to follow the circuit. It looks like - and I could be wrong, so don't hold me to this - they shut down the 12V standby supply when the main converter is running to save energy (the 12V SB output is supplied from the main converter rather than the separate SB converter when not in standby). I've read rumours of that happening in modern supplies, but HP were ahead of the game if that's what they're doing with this relatively old PSU.
It looks like the presets are related to the current sensing, which tallies with your earlier experiments. If I ever discover what resistors you need to change to alter the 12V output, I'll let you know, but until then, I wouldn't drill the hole in the front panel for the pot. But then, I don't think my question about supply voltage (how much practical difference does it actually make?) was answered, so in the absence of that, you'll have to forgive me for not giving it a huge amount of priority for the sake of a dB or thereabouts.
It looks like the presets are related to the current sensing, which tallies with your earlier experiments. If I ever discover what resistors you need to change to alter the 12V output, I'll let you know, but until then, I wouldn't drill the hole in the front panel for the pot. But then, I don't think my question about supply voltage (how much practical difference does it actually make?) was answered, so in the absence of that, you'll have to forgive me for not giving it a huge amount of priority for the sake of a dB or thereabouts.
