I got one of these, replaced the onboard battery, hooked up into the main battery plug with my bench power supply, and I am not able to get it to show anything on the screen, other than a long horizontal line that can move down the whole screen.
I went through the technical manual and so far, I've gone through the validation that the 7508 (7501 in actuality) is working.
Pin 23 goes high when power switch is on (only after an initial reset)
Pin 5 goes high, so there is main battery power.
Pin 35 goes low when I do an initial reset and returns to normal high.
Pin 36 goes low and stays that way, as I'm not plugged into power and it's not going to go into trickle charge mode.
Pin 37 is low, bit it can go high if I vary my power supply to lower than 4.8v. It seems to stay that way even if I raise the voltage back up to 5.4v
Pin 28 is low, so no it's not recharging
Pin 30 is low, so the aux battery would go into normal charge, voltage on it is 5.1v so it seems fine.
Pin 14 goes low when powered on, stays low even when the power switch is flipped, only goes high and stays that way if I hold the initial reset.
Pin 15 is low.
So, power control appears to be working. The fact that the screen can draw a line across (normally if I hit that initial reset while its powered on) tells me the screen should work.
Q23 has 5v, Q20 has about 8.5v and Q6 also has 5v. Q9 is only active if I plug in the charger, so I'm assuming that's related to the charging circuit.
I've adjusted the V3 because it was reporting about 230khz on the CL2 test point, so now it shows a 199/200khz as the manual states it should be about 200.
I've not gotten any beeps out of the system, but I can get some scratchy noises if I touch pin 5 of the 6301.
VRF is showing between 1.8 and 2.0 depending on the main battery voltage, and goes to 1.75 or so if the main battery voltage is about 4.8, so I don't think the other variable resistor needs to be changed. All other voltage test points seem fine, about 5v.
Anyone know what else to try? The whole board looks completely fine, no bulging caps, no green splotches, it's mint condition. I don't think I need the tape drive connected to power it up, but I don't know that for a fact. I've tried it with that connected and nothing changed.
I went through the technical manual and so far, I've gone through the validation that the 7508 (7501 in actuality) is working.
Pin 23 goes high when power switch is on (only after an initial reset)
Pin 5 goes high, so there is main battery power.
Pin 35 goes low when I do an initial reset and returns to normal high.
Pin 36 goes low and stays that way, as I'm not plugged into power and it's not going to go into trickle charge mode.
Pin 37 is low, bit it can go high if I vary my power supply to lower than 4.8v. It seems to stay that way even if I raise the voltage back up to 5.4v
Pin 28 is low, so no it's not recharging
Pin 30 is low, so the aux battery would go into normal charge, voltage on it is 5.1v so it seems fine.
Pin 14 goes low when powered on, stays low even when the power switch is flipped, only goes high and stays that way if I hold the initial reset.
Pin 15 is low.
So, power control appears to be working. The fact that the screen can draw a line across (normally if I hit that initial reset while its powered on) tells me the screen should work.
Q23 has 5v, Q20 has about 8.5v and Q6 also has 5v. Q9 is only active if I plug in the charger, so I'm assuming that's related to the charging circuit.
I've adjusted the V3 because it was reporting about 230khz on the CL2 test point, so now it shows a 199/200khz as the manual states it should be about 200.
I've not gotten any beeps out of the system, but I can get some scratchy noises if I touch pin 5 of the 6301.
VRF is showing between 1.8 and 2.0 depending on the main battery voltage, and goes to 1.75 or so if the main battery voltage is about 4.8, so I don't think the other variable resistor needs to be changed. All other voltage test points seem fine, about 5v.
Anyone know what else to try? The whole board looks completely fine, no bulging caps, no green splotches, it's mint condition. I don't think I need the tape drive connected to power it up, but I don't know that for a fact. I've tried it with that connected and nothing changed.
