Andy Jackson
Well-known member
Hello guys!
I have an old Juno 6 which is in a sorry state. The old girl cosmetically is pretty shook up, but internally (visually) it seems fine. On first measuring the PSU, there was no +15V or -15V on the board. I duly replaced all of the electrolytics, and remeasured. Nowt.
I reckon that the +/- regulator (an old TA7179P) has probably shuffled off this mortal coil. I then remembered that the little MNats PSU (with the LM317/LM337 combination) could output the + or - 15V required.
Looking at the schematics of the Juno 60 which has an identical circuit for this part of the PSU (attached), it seems that a supply capable of supplying 1A max. should do the trick here - and I'm sure I read somewheres that the MNats Little PSU is capable of safely supplying up to 1A.
I connected the secondaries to the MNats PSU board, and powered up, and adjusted the variables so I had 15V at the outs. All good so far. However, the regulators are running EXTREMELY hot.
I then measured the secondaries directly with no load which gave 22V on both. Am I correct in assuming that we're looking at 30V in to the regs in the PSU after rectification? Which means that they have to dissipate a LOT of heat (around the 26W mark) when regulating down to +/-15V? I was thinking of the series resistor option (something like a 5.1 ohm / 50W job) to try and get the regulators not working as hard, and also to get the temperatures down a tad...along with a heatsink of sorts...
I suppose I just need a critical eye cast over my thoughts, which would be much appreciated. I'm really hoping to get the old girl up and running again.
Best wishes & thanks in advance!
Andy.
I have an old Juno 6 which is in a sorry state. The old girl cosmetically is pretty shook up, but internally (visually) it seems fine. On first measuring the PSU, there was no +15V or -15V on the board. I duly replaced all of the electrolytics, and remeasured. Nowt.
I reckon that the +/- regulator (an old TA7179P) has probably shuffled off this mortal coil. I then remembered that the little MNats PSU (with the LM317/LM337 combination) could output the + or - 15V required.
Looking at the schematics of the Juno 60 which has an identical circuit for this part of the PSU (attached), it seems that a supply capable of supplying 1A max. should do the trick here - and I'm sure I read somewheres that the MNats Little PSU is capable of safely supplying up to 1A.
I connected the secondaries to the MNats PSU board, and powered up, and adjusted the variables so I had 15V at the outs. All good so far. However, the regulators are running EXTREMELY hot.
I then measured the secondaries directly with no load which gave 22V on both. Am I correct in assuming that we're looking at 30V in to the regs in the PSU after rectification? Which means that they have to dissipate a LOT of heat (around the 26W mark) when regulating down to +/-15V? I was thinking of the series resistor option (something like a 5.1 ohm / 50W job) to try and get the regulators not working as hard, and also to get the temperatures down a tad...along with a heatsink of sorts...
I suppose I just need a critical eye cast over my thoughts, which would be much appreciated. I'm really hoping to get the old girl up and running again.
Best wishes & thanks in advance!
Andy.