NeXT
Veteran Member
This has been my project ever since 'rona mania flared up. It's an early 1970's Class 250 electronic cash register manufactured by NCR and using core memory. Could also be a networked terminal. All I know is that at one point it was operating standalone. Likewise it showed up a complete disaster and had to be almost entirely stripped, cleaned, reoiled and repaired.
There's a bit more than jsut spit and polish that went into making this shine again.
Okay, so here's where the fun starts. It runs a 400w linear power supply that came up seemingly fine after all the big caps were reformed. It was dirty and the power resistors all showed their age but it hasn't so far given me any troubles.
So now it turns on, the cooling fan works and I can trigger the print motor if I push the receipt advance button, but the advance mechanism relies on the digital side and that doesn't seem to want to come up. In fact, nothing wants to come up. The display remains blank, the keypad does nothing and it doesn't make any noises.
I've made a tread previous about this here about the memory. The electronics are really, really early IC tech. Some chips have date codes from 1971! NCR has gone through their parts and relabeled everything to their own internal part numbers and the only databook I found on bitsavers seems to be too new to list anything. I also sanity checked and cleaned and reseated every plug and edge connector in the machine while checking for any obvious shorts or smaller cap issues. thermal camera complains about a 22mfd50v axial in the display section but otherwise I'm not seeing any grossly overheating components. In fact I'm not seeing most of the IC's give off heat, but the scope at least says there's signals moving around at the test points so....yeah no idea if I'm missing volts or these just are not as power hungry as I'm expecting. I have no datasheets on what to expect from the power supply.
The only way I've managed so far to make it do much of anything was to either press SP2 on the control unit, then it beeps, displays CLEAR ERROR on the display and after six seconds blanks the display, beeps and lights the indicator again...OR by accident I found that if I grounded my scope lead on the black test point on the control unit and poked my probe at the orange test point on the terminal clock board, it might beep, it might run the motor, it might fire a few relays or it might even light up the entire display. Either way, it doesn't like it when I'm scoping using the wrong ground but it still twitches its leg.
I don't know how to proceed from here. I have no service docs, no cross references and the boards are all buried under the keypad assembly which makes them hard to probe pins while running so randomly poking around is a massive pain. Does anyone else have good pointers and what to do next? High resolution images of the boards, front and back, are available here --> https://imgur.com/a/nnDAhRy
There's a bit more than jsut spit and polish that went into making this shine again.
Okay, so here's where the fun starts. It runs a 400w linear power supply that came up seemingly fine after all the big caps were reformed. It was dirty and the power resistors all showed their age but it hasn't so far given me any troubles.
So now it turns on, the cooling fan works and I can trigger the print motor if I push the receipt advance button, but the advance mechanism relies on the digital side and that doesn't seem to want to come up. In fact, nothing wants to come up. The display remains blank, the keypad does nothing and it doesn't make any noises.
I've made a tread previous about this here about the memory. The electronics are really, really early IC tech. Some chips have date codes from 1971! NCR has gone through their parts and relabeled everything to their own internal part numbers and the only databook I found on bitsavers seems to be too new to list anything. I also sanity checked and cleaned and reseated every plug and edge connector in the machine while checking for any obvious shorts or smaller cap issues. thermal camera complains about a 22mfd50v axial in the display section but otherwise I'm not seeing any grossly overheating components. In fact I'm not seeing most of the IC's give off heat, but the scope at least says there's signals moving around at the test points so....yeah no idea if I'm missing volts or these just are not as power hungry as I'm expecting. I have no datasheets on what to expect from the power supply.
The only way I've managed so far to make it do much of anything was to either press SP2 on the control unit, then it beeps, displays CLEAR ERROR on the display and after six seconds blanks the display, beeps and lights the indicator again...OR by accident I found that if I grounded my scope lead on the black test point on the control unit and poked my probe at the orange test point on the terminal clock board, it might beep, it might run the motor, it might fire a few relays or it might even light up the entire display. Either way, it doesn't like it when I'm scoping using the wrong ground but it still twitches its leg.
I don't know how to proceed from here. I have no service docs, no cross references and the boards are all buried under the keypad assembly which makes them hard to probe pins while running so randomly poking around is a massive pain. Does anyone else have good pointers and what to do next? High resolution images of the boards, front and back, are available here --> https://imgur.com/a/nnDAhRy