Hi there. I have a plastic case ESQ-1 that is blowing fuses 1 and 2 (2 amp 250v fuse). I received the synth non working, so unfortunately I have no history. I tried disconnecting the key bed and sound Cartridge module from the main board in attempt to rule those out, as I’ve heard if the cables are plugged in backwards can cause shorts. I carefully inspected the boards and can see no visible signs of trouble. Any idea where I can start trouble shooting? I have intermediate skills and would love to learn more about repair, so don’t want to take for repairs unless all options are exhausted. The board is in excellent condition otherwise, so I am thinking it has set non-working for years.
Thanks for any help I can receive here. I’ve had great luck in the past getting help from this forum and its appreciated!
First - remove the connectors which feed power to the display and main board - J2 and J3 on the power supply.
Then power up the synth and see if the fuses still blow. If they blow then problem is in the power supply and should be an easy fix.
If the fuses don’t blow then start connecting the J2 and J3 connectors one at at time to see if it’s the display or main board blowing the fuses.
Pat, thanks for the tip. The fuses are still blowing after disconnecting the display and main board connectors. I suppose I will recap the power supply board and go from there, as they are the original caps. Any other components you recommend changing or are know to go bad on this synth? Thanks again I really appreciate the help. Can’t wait to hear this synth work!
Next i would check the diodes (CR1 thru CR6). Disconnect the J1 connector which comes from the transformer. Use a meter that has diode checking capability. With your meter leads connected across the diode you should get approx 0.6 volts in one direction. Swap the meter leads and you should get an open circuit.
Have you verified what all voltages are produced out of the power supply? The Roland A33 MIDI has aboard that switches between wall plug supply (check correct polarity between the two) and battery. The plugs internal to the main board have 9v and regulated 5.8v which is a NPN transistor follows a Zeaner diode. Would need to see the schematic. Sorry if this is to obvious.