First post, by Jonas-fr
I've got a Roland SB-55. It's a floppy-based MIDI player, little brother of the mighty SC-55. The SB-55 basically read .MID files on a floppy and plays them through it's MIDI OUT port (it also can record from its MIDI IN port onto a floppy).
The problem with my SB-55 is that when I plug the DC adapter the 3 number LCD screen give me three middle dashes "---" and no buttons seems to be working not even the power button. If I unplug it and replug it the unit seems dead, no status light, nothing on LCD this time, no button reaction. If I unplug it, wait a few minutes and replug it I get the 3 dashes again. One more thing under "the three dashes state" the FDD reacts when I insert a floppy: the main motor spins but the heads don't seek; under the blank LCD state the FDD spins its motor only one second after inserting a floppy then stop it as if it lacked electricity. In both cases the FDD status light is always on (even when the motor stops in the "blank LCD" state).
Since I didn't find a Service Manual for the SB-55 (I'm usually fairly efficient into finding service manuals so I'm guessing it doesn't exist or it isn't public) I looked upon the owner manual in the troubleshooting section but nothing about 3 dashes message. I sent a request to Roland but no answer yet.
Knowing a bit about electronics I've made this diagnostic (it could be one or more of these IMO):
- the floppy drive is dead or the power supply is bad
- the main capacitor (C205 - 16V 2200µF) is dead
- the main EPROM (IC10 - 27C512 EPROM) is dead or it's ROM binary is corrupted
- one or more of the five other small SMD capacitors (16V 47µF) is dead
I replaced the FDD with a working one (with good jumpers configuration) and also with a FDD emulator (HxC based): it didn't change anything
I checked the power supply to the FDD and it gave me 5V so it is OK.
I replaced the main capacitor with a new one: DIDN'T CHANGE ANYTHING
So this is where I am. I never recapped a board with SMD components, I'm not good/precise enough to do it so I let this option as last resort (I still have bought replacement SMD capacitors).
TL;DR I'm now looking for a ROM image of a working Roland SB-55. So if you've got one and are willing/competent to dump it's main EPROM (it's socketed so you don't have to desolder anything, just remove some philips screws to access it, it's very easy!) you'll greatly help me into saving one of these rare beasts! If you've got a working SB-55 but don't have a chip dumper you can send me your chip (I'll pay for the shipping of course and can give you a little extra for the hassle).