SE/30 Black screen but works otherwise

[egrath]

Hi,
i got a non working SE/30 (did not come up, no chime, ...). At first i thought it was a defective logic board as the caps nearly felt off just by looking at them, so i replaced all of them, but still no luck:
- After powering on, the chime is played, the hard drive starts spinning up and even boots the system. I know that it has been booted, because after a few minutes i suppose that some kind of screensaver installed is kicking in and starts playing nice, relaxing sounds.
- The monitor stays completely black, but i assume that it has power as there's a static charge building up in front (don't know how to explain properly, you can feel it with your hands when slightly touching the display)
Any hints on how to properly proceed in analysing the issue and getting the device to work? It's my first non working macintosh, so i have no experience with macintosh specific issues.
Thanks, Egon

 

[joshc]

Reflow the yoke connector on the analog board with new solder because they are subject to weak/cracked solder joints

Reseat the yoke board, they can come loose in transit

Check power supply voltages from the floppy port:

 

[pocketscience]

I assume you checked the brightness knob under the CRT...?

 

[PacificState]

I had this and it turned out to be dry joints on the yoke board.

 

[egrath]

Just removed the Analog board for inspection, but started with the Power supply.

Sony CR-44 PSU gives me the following readings: (standalone, no load connected)

Pin 4-GND +5.57 V
Pin 5-GND +11.16
Pin 6-GND -8.30 V (-12.49 V for 1/3 second, then settles at -8.30 V)
Pin 9-GND +5.56 V
Pin 10-GND +10.56 V

The -12 V rail seems a little odd to me, as it shows -12.49 V when measuring but almost immediatly settles down to -8.30 V. Can anyone verify if those numbers/behavior is correct for a SE/30 power supply?

 

[amedeo_68k]

-12V is not used by SE/30 itself, it is just passed through PDS slow or expansion board (if needed), btw, -8V is odd.
Do you have a spare logic board, from any other SE or SE/30, that you can put in and test ? just to be sure that the issue resides on analog board.
(Also analog board and PSU need recapping)

 

[egrath]

-12V is not used by SE/30 itself, it is just passed through PDS slow or expansion board (if needed), btw, -8V is odd.
Do you have a spare logic board, from any other SE or SE/30, that you can put in and test ? just to be sure that the issue resides on analog board.
(Also analog board and PSU need recapping)

Yes, i pulled the logic board from my working SE/30 to make sure that my solder job didn't caused the problem. The board i recapped yesterday works in the other SE/30, but not the other way round. So i strongly assume that the issue is somewhere in the Analog or CRT yoke board. Just measured R22, CR2 and CR3 - they look good with a forward drop of 0.3 V for the diodes and 420 kOhm for the resistor.

As the previous owner mentioned he "had some issues with the brightness knob" i measured that too: resistance goes from 5 Ohm to 700 kOhm

 

[egrath]

Reflow the yoke connector on the analog board with new solder because they are subject to weak/cracked solder joints

Did that right now, the connector is now sturdy as hell and has a good connection when measuring from the pins to other connected solder joints. Unfortunately, no difference.

Question: The yoke board is the pcb which sits on the backside of the CRT which controls the electron gun?

 

[amedeo_68k]

Did that right now, the connector is now sturdy as hell and has a good connection when measuring from the pins to other connected solder joints. Unfortunately, no difference.

Question: The yoke board is the pcb which sits on the backside of the CRT which controls the electron gun?

No, the joke connector is the big connector ( 4 poles ) that goes to the joke coil, on the neck of the crt, where you all the copper around.

Did you try to put another power supply ?
Have you recapped the analog board ?

one more thing,...when Mac is on try to turn off room light, is there a little light at the backside of crt ?

 

[egrath]

Hi, today i replaced the Analog board with a known good one and it works, so i assume a issue with the Analog board. Eventually i really need to recap it completely.

There's a slight glimmer visible on the back of the CRT when it's powered on, similar to a very weak neon lamp. Does that mean that the CRT is actually getting power but no control signals?

 

[amedeo_68k]

It means CRT is alive. But if you tested with another analog board, then ok. Try to recap it. In the worst case could be the flyback transformer

 

[egrath]

Regarding the Flyback transformer: As far as i understand CRTs, the flyback is responsible for producing the high voltage sawtooth waveform used to drive the electron beam. I built my own grounding tool to discharge the CRT before working inside to make sure it doesn't kill me. On various sources they state that in the process of discharging, a snap should be very hearable, similar to the one you hear when you personally build up static charge and touch a metal part. That hasn't occured once with the not working Analog Board. After testing with the good Analog board, i heard it for the first time from this SE/30.

 

[amedeo_68k]

The flyback transformer of SE and SE/30 has an internal discharge resistor. So you may not hear the discharge crack. But it is always safe to discharge.