SE/30 freezes a few seconds after boot

[my03]

Hi,

i have an se/30 that have been working beautifully for quite many years. Its equipped with a scsi2sd and i also have the Rominator II from BMOW.

2 years ago, i had the "simasi" pattern on the screen and so i ordered the recap-kit and replace all of them. After this, it worked 100% again, until yesterday. Now when i power on, i get the chime and i see the mouse-pointer on the screen. I can move the mouse for ~5 seconds before everything freezes. Restarting the machine only repeats the above.

I wonder if this behaviour could be caused by non-connectivity of the ROM? I get no errors or such.

 

[NeXT]

Does it lock solid with the SCSI2SD attached or will it sit forever at the blinking question mark?

 

[my03]

Hi NeXT,

It locks with and without the scsi2sd in place (totally disconnected scsi and power/molex). Only thing i see is a very clear screen and the mouse-cursor that stops moving after a few seconds and stays frozen. I will try to disassemble it and remove the memory from it to see if that makes any difference. I tried earlier to visually inspect the board for anything out of the ordinary but could not see anything with the naked eye (potentially, it requires proper magnifyers, i agree).

 

[my03]

I noticed another thing also. The floppy does not read disks any longer. I started to suspect the PSU and stumbled across this document:

SE/30 Forever - Macintosh SE/30 Power Supply

This aims to be the most exhaustive collection of resources for the Macintosh SE/30 computer on the World Wide Web.

se30forever.com

where #3 and #4 are (unfortunately) part of my problem here. While this doesn't necessarily cause major issues for me (i have soldered a bit in the past, fixing pc systemboards, synthesizers etc) i'm quite reluctant to fiddle to much with the se/30 screen (the high voltage). Is there some rule of thumb for how long the computer needs to be off the power grid (completely disconnected) before the risk of getting zapped is low? a day? week?

 

[GiGaBiTe]

se/30 screen (the high voltage). Is there some rule of thumb for how long the computer needs to be off the power grid (completely disconnected) before the risk of getting zapped is low? a day? week?

CRTs are essentially giant capacitors, they can hold voltage for a VERY long time. I've personally seen them hold a charge for well over a week. Many flyback designs have bleeder resistors in them to drain the tube charge, but these resistors can fail open and not work.

I would recommend a flat screwdriver with an insulated handle, a 1 megohm resistor and a wire to the CRT mount. Poke the screwdriver under the anode cap and touch the screwdriver to the anode for a minute or so to discharge the tube.

 

[my03]

Thx GiGaBiTe,

i'll muster the courage to try it out. I found this video showing the procedure (minus the resistor in this case), but as i just recently ordered a recap-kit, i assume it will be more than 7 days before it is delivered (but i'll still do this procedure for good measure)

best regards

 

[GiGaBiTe]

The resistor is to protect the tube and flyback from damage from sinking a huge amount of current instantaneously. While you can directly short the anode cap to ground without a resistor, I don't recommend it.

 

[MattisLind]

I never use a resistor when discharging the tube. The only stored charge is in the tube and it isn’t that much of energy. Since there is no charge stored in the flyback no current will flow through it. I wouldn’t think that a quick discharge of the tube would cause any dammage. Besides the diode in the flyback has som leakage so after a few hours there is not much left. https://lowendmac.com/2007/the-truth-about-crts-and-shock-danger/

Not saying that you should’t use a series resistor. Just that I don’t see any point in doing so. I just use a earthed screwdriver which I push under the anode cap.

 

[Timo W.]

Check the Apple service manual. For some models they say you need a resistor, for others you don't. It depends on the model's design.

Let it sit for a week with no power and then discharge without a resistor. If you never did it before, that is the safest way. After a week, most - if not all - stored energy is gone. And not using a resistor has the advantage that you hear a "click", should there still be any engery left that discharges. With a resistor, you never know if something has happened at all.