derkom's doings

[derkom]

I decided to get started on the STE booster installation today, and quickly ran into a problem: The STE I was doing to install it in doesn't run reliably anymore. It's been several years since this one was powered up.

It's behaving a bit curiously. At first it seemed like it was fine, but then it became apparent that it's only briefly willing to run, and how long it will run depends on how recently it's been on. We're talking seconds here, too. A totally cold start, it seems to run for about 30 seconds before it goes to black screen. If I let it sit at that point for 10 minutes, it might run for five seconds. If I let it sit for just a couple of minutes, it will run for under a second.

When I plug in the diag cart and hook up serial, it typically is spitting out a few lines (or even just a few characters) of the startup output before simply stopping cold.

I've tried three different PSUs, including the one that happily runs the H4 for days at a time. I think it is not a temperature-related problem because it isn't running long enough for anything to get warm. Given the relationship between run time and wait time, my hunch is that it's a problem with the motherboard caps, which I presume are original, but I wonder if this looks familiar to anyone else.

[exxos]

Are the power supplies recapped though, the STE is not as forgiving as other machines like STFM etc.

I would also clean the contacts on the RAM,ROM,CPU.

[PhilC]

@derkom does it go to a total black screen? If so its possible the psu has shut down due to a short circuit?

[derkom]

Are the power supplies recapped though, the STE is not as forgiving as other machines like STFM etc.

They're not, actually. That's also on my list of things to get accomplished. I've got a new PSU in the working STE, so I'll pull that out and test it. (Didn't want to have to dig into that system if I didn't have to, as it's actually screwed shut!)

I would also clean the contacts on the RAM,ROM,CPU.

Sure, certainly wise to do that before any major surgery. :)

[derkom]

@derkom does it go to a total black screen? If so its possible the psu has shut down due to a short circuit?

Total black screen, no sync even. PSU output still looks fine on a multimeter.

[PhilC]

Have a good look at the bottom of the board for corrosion and as exxos says, clean up the contacts etc.

Probably dry joint somewhere due to corrosion.

[derkom]

Same behaviour with the Centuriontech PSU. I probably won't get any further on this tonight, as I got started rather late, but I'll dig a little deeper tomorrow.

When powering up with the Centuriontech PSU, which meant the system had been sitting a while, I got all of this (yes, including the truncations):

Code: Select all

16 Checking exception handling...

K1 Keyboard not responding
Keyboard failed, connect RS232 terminal

E9 Ba
E8 Bus
E9 Bad instruction
E
E8
E9

E9
E9
E9 Bad instruction fetch

Keyboard error is expected, as it's not hooked up at the moment. The rest is kind of curious, especially the truncated lines. After that last E9, there is nothing further.

[exxos]

Must have a bad connection on the address or databus, might be worth just re-soldering the CPU socket.

[derkom]

No further investigation done yet today, but powering up the system having sat unplugged overnight, I get the full diag cart startup sequence on serial, followed by the menu, followed by death. Total runtime about five seconds.

[derkom]

I don't like the quality of the TOS sockets on the STE, so I decided to eliminate that variable by going ahead and removing them and soldering in the TOS switcher board. At first I thought the problem was solved, because it made it through a whole series of internal tests, but then it threw a RAM error, followed by a reboot, and now is back to doing nothing unless I let it sit a while. I'll go ahead and resolder other parts of the bus, although I hate to add any more solder to the CPU socket when the whole idea here is that it's coming out! :lol: At least the solder sucker makes pretty short work of this stuff.

IMG_20200519_130913.jpg