Sounds just like the supply on my Altos. What a pain. Eric Smith <space...@gmail.com> wrote:
>I previously wrote about the monitor of my Intel Series II MDS going >out, which was because the +15V DC supply tripped the crowbar. The >voltage adjust was all the way to the minimum, and the voltage was >still about 17.4V with no load, and trips the crowbar with even a >small load. I think someone previously encountered this problem and >adjusted the pot rather than fixing it, and the problem has gotten >worse since. > >The root cause of the failure appears to be that the internal voltage >reference of the uA723, which is specified as 7.15V ±0.35V, is now >9.4V. The uA723 needs to be replaced. The uA723 is still readily >available, but due to the construction of the power supply, replacing >it is relatively difficult. Just probing the pins of the chip was a >challenge. The pass transistors are mounted to 1/8 inch aluminum >plate, but the pins are soldered into rivets in the single-sided PCB, >entering from the etch side (which is closest to the aluminum), so >they will have to be desoldered to get at the etch side to replace the >723. I considered just cutting the pins of the 723 and soldering >another (or a socket) onto it from the component side, but pins 1-7 of >the 723 are right next to a big axial electrolytic so there's no way I >can solder that side. Input and output wires to the board are soldered >into single-pin cup thingies on two opposite edges of the board, so I >can't even get the board into an orientation suitable for working on >it without desoldering or cutting some of the wires. > >I haven't bench-tested the monitor, because I haven't kludged up a >suitable signal source yet, but I don't think there's anything wrong >with it.