Hi all,
I recently bought an old Roland SH-2 from Japan which had the original 110V transformer inside. I hooked it up with a step down converter and every function worked perfectly (to my suprise).
I then set about converting to UK 230V with a new transformer. All wired up and powered up ok with the power and LFO LED’s lighting up (didn’t test audio as was in my workshop). I then went to try it out in my studio the next day and after 10 seconds or so the LED’s faded and the unit no longer had power.
I disconnected power from the main synth pcbs amd poked around the power pcb with my multimeter and I’ve blown the internal fuse. Now, its highly likely that the 45 yr old fuse just blew and I may just need to throw in a new 250ma 250V rated fuse and all will be well (these are on order) But the SH2 service manual has different switch specifications for 110V and 220V. Is this really needed? Others on youtube have kept the original switch but I’m trying to gauge how neccesary this is?
I suppose when the fuses arrive I can test and if a new one blows immediatly I’ll have to try a new switch. Although the switch listed on SYNTAUR has no specifiaction for voltage level?
Any advice would be much appreciated if anyone has come across anything similar with converting old japanese synths!
Yes, in general it’s important to use such a switch and set it for the correct source AC voltage. There are typically other internal components like resistors, regulators, etc. that determine current supplied, involved on the PCB. Note that one position if wrong can cause only half the required voltage expected to under power everything else while missetting the switch in the other position can… well very bad things… like twice the voltage and current… and poof. IMHO it’s unconscionable to not label such a vital setting on the switch, on the case opening, and/or, the pcb silk screened lettering. If the board or switch is out of the case currently (pun) you certainly should inspect all 3 locations for label indications. Good luck.
The importance of having the correct switch is so that arcing can’t occur between switch contacts. While this is problematic because it could lead to the switch ultimately failing (perhaps after years), it wouldn’t cause a surge in current to blow a fuse.
Before swapping fuses I’d measure the voltages on the secondary side of the transformer and make sure everything is looking good there. As long as you chose a transformer that gives the correct voltages on the secondary side it should be a fine substitute and not cause issues.
Has this unit received any other service? Old electrolytic capacitors in the power supply are common causes of fuses blowing. Did you run this synth much before attempting the modification? Sometimes it takes a few hours of run-time before all problems show themselves on a vintage synth, especially if it hasn’t been powered on in a while.
Just adding an update to the situation if anyone in the future comes across this. I replaced the fuse and added a modern fuse holder and the synth has been powering on fine and working ever since. My theory is that the 45 yr old internal fuse had never seen 240v (bought the synth from japan) before and just blew becuase it was so old.
I do plan to swap out the caps on the power board just to be sure. But if anyone is in doubt - from my research many people have converted SH2’s and SH09’s to 240V and do not change the switch so it may be overkill with these old rolands.
That said theres no real risk as if the switch does arc one day it will just pop the fuse again and can be easily replaced.