jpmorris
Tape Wolf
I am using an Otari CB140 remote unit with an MX80 24-track machine. It has been a little cantankerous, occasionally blowing the 2A internal fuse, especially if the unit was knocked. The other day, it threw a strop and now is blowing fuses continuously. I am still investigating, but I'm posting what I have discovered so far in case anyone else is interested or has a similar problem.
The CB140 takes power from the MX80 via the D-sub connector. Pin 1 is the chassis ground, pins 16 and 17 are an unregulated 24v DC supply (they are connected together). The other pins are 19 for the tach signal, plus a bunch of others to set up a balanced RS422 serial interface to the deck.
The CB140 takes the 24v supply and by some convoluted means converts it to a regulated 5v DC output to power the system logic. The guts of it is an STK772B chopper regulator of which there is very little information available, and almost the entire circuit board is taken up by support components. The regulator itself is attached to a massive slug of aluminium as a heatsink. The later output stages involve a triac, for reasons I do not comprehend.
The PSU board is thus:
When we see the reverse side, things start to get ugly. Someone has been dicking around with it, cutting tracks off the board and attaching these strange globes, which I think may be some esoteric form of zener diode, but look like some kind of alien technology, or would if they glowed.
I've replaced the electrolytics. The PSU board blows fuses even when disconnected from the motherboard which simplifies things a bit - going by the schematics the only other components after the fuse are the triac, a zener diode, and a mylar capacitor. I have sourced a replacement triac, but not the other suspect parts. In any case the board has some extra weirdness not on the schematics, and I have to wonder if the tacked-on globes or the cut traces are somehow shorting - the fact that it tended to blow fuses when knocked does make me wonder.
At this point I'm starting to run out of 2A fuses as well as patience, so my current plan is to do away with the entire board, and replace it with a 5V DC-DC converter off ebay. As I write this I have actually managed to get the remote to boot and operate by patching a USB charger to the 5V line on the motherboard, but this is a complete bodge.
It may be of interest to note that if the remote is powered independently like this, with the remote booting up before the deck is powered, it will display Error 90, and then establish connection to the deck later once that has been powered up.
One thing that disturbs me is that using a continuity tester on the motherboard, the 5v and Ground test points appear to be shorted together. This persists unless CN5 is disconnected, which is the ribbon connector for the transport buttons on the remote control. Since I am more interested in recording my song than experimenting on the fragile innards of an already sick remote control I have left this disconnected for now, but I would be interested to know if anyone else with a CB140 can take the same measurements and let me know if that's normal (i.e. the Fluke is seeing ghosts).
The CB140 takes power from the MX80 via the D-sub connector. Pin 1 is the chassis ground, pins 16 and 17 are an unregulated 24v DC supply (they are connected together). The other pins are 19 for the tach signal, plus a bunch of others to set up a balanced RS422 serial interface to the deck.
The CB140 takes the 24v supply and by some convoluted means converts it to a regulated 5v DC output to power the system logic. The guts of it is an STK772B chopper regulator of which there is very little information available, and almost the entire circuit board is taken up by support components. The regulator itself is attached to a massive slug of aluminium as a heatsink. The later output stages involve a triac, for reasons I do not comprehend.
The PSU board is thus:
When we see the reverse side, things start to get ugly. Someone has been dicking around with it, cutting tracks off the board and attaching these strange globes, which I think may be some esoteric form of zener diode, but look like some kind of alien technology, or would if they glowed.
I've replaced the electrolytics. The PSU board blows fuses even when disconnected from the motherboard which simplifies things a bit - going by the schematics the only other components after the fuse are the triac, a zener diode, and a mylar capacitor. I have sourced a replacement triac, but not the other suspect parts. In any case the board has some extra weirdness not on the schematics, and I have to wonder if the tacked-on globes or the cut traces are somehow shorting - the fact that it tended to blow fuses when knocked does make me wonder.
At this point I'm starting to run out of 2A fuses as well as patience, so my current plan is to do away with the entire board, and replace it with a 5V DC-DC converter off ebay. As I write this I have actually managed to get the remote to boot and operate by patching a USB charger to the 5V line on the motherboard, but this is a complete bodge.
It may be of interest to note that if the remote is powered independently like this, with the remote booting up before the deck is powered, it will display Error 90, and then establish connection to the deck later once that has been powered up.
One thing that disturbs me is that using a continuity tester on the motherboard, the 5v and Ground test points appear to be shorted together. This persists unless CN5 is disconnected, which is the ribbon connector for the transport buttons on the remote control. Since I am more interested in recording my song than experimenting on the fragile innards of an already sick remote control I have left this disconnected for now, but I would be interested to know if anyone else with a CB140 can take the same measurements and let me know if that's normal (i.e. the Fluke is seeing ghosts).