Power supply problem secondary double voltage (korg m1)

[tedsorvino]

Hi all. After a stupid mistake i’ve made (wrong power connector) i found a shorted power supply in my old kirg m1 (befire any further tests).
Disconnected the power supply from the nainboard, took it out and started testing it. Replaced the fuse and after some trial- error (some small shorted components) the first problem came down to a totally shorted q1. Replaced it with a 2sc2335 i had around (good equivalent of the original 2sc3570 according to thus guide https://alltransistors.com/crsearch...400&ueb=6&ic=5&tj=125&hfe=40&caps=TO220&cf=on). I’m not certain if the transistor is in perfect shape.
All seemed ok, but i realized that the secondary was giving double figures. 10v instead of 5v on the 5v rail, and +-24v on the +-12v rail.
The transformer is not shorted (but other than that i can’t tell details about primaries - seconadries ratios since none is given).
I guess the problem lies before or just around the 4 pins of transformer T1.
Has anybody any specific ideas what the problem can be and which components could csuse such a problem.
I attach the m1 service manual. The pcb i’m fixing is klm 1267,1268 (it’s 1268) on pate 11 of 28.

Thanks in advance

 

[Khron]

Have you tried adjusting VR1 and see if it has any effect?

Some dummy-load on the 5v output might help too - the feedback network may well have been optimized for loaded conditions, and is really out-of-whack unloaded.

 

[tedsorvino]

Thanks for the reply. The trimmer is in the mv range so it’s just for fine tuning of the 5v rail. Doesn’t take that rail below the 10+V at the moment.
Load makes no difference. Have tried it with and without in the past. And all voltages were fine. Now all double,
I repeat that the voltages are not all over the place. They are EXACTLY double. Like a divider is missing.