derkom's doings

[JezC]

@derkom Great news - very glad to hear :thumbup: that the surgery appears to have gone well!

[derkom]

A curious development. GEMBench ran just fine for several hours last night, so today I did the booster install, which seemed to go fine, but when I powered up the system, the video was a little bit shaky, then when trying to run GEMBench, I got some bombs (didn't get a chance to count, but something around 10), and then the "system out of memory, use foldr100" message. And when I restarted, I'm back to exactly the same glue behaviour as before, where I briefly have sync, and then it goes away. Same thing happens at 8 MHz.

So it looks like I've got another dead glue, which means something is wrong with this board that is killing glues. I don't know why it ran just fine for hours last night, but I am back to square one with this board, only with a really nice booster installed on it. :)

[exxos]

Your not using parity simms are you ?

[derkom]

Your not using parity simms are you ?

Nope. Just plain old 256k SIMMs at the moment. Never upgraded this system past 1 MB (but obviously plan to if I get it working).

There may be something else amiss here, but producing the same symptoms as before. Now that I pulled out the scope, I see that the glue is only very briefly seeing a clock signal on pin 2, so I'll be tracing that back now to see what's causing that problem.

[derkom]

Okay, after numerous things happening (*), I finally have this...

IMG_20200607_122808.jpg

It's still not 100% stable, and I don't know why. It took a couple of resets to get it to boot, and then GEMBench crashed during its first run, but now it seems stable. Will try swapping out memory, etc.

Diag software is all passing except the RAM test, which passes at 8 MHz, but fails at 32 MHz. Is this perhaps expected behaviour?

* So yesterday I was back to seeing similar symptoms (no sync), but upon inspection it became clear that this time, the Glue was not receiving a good clock. Tracing that stuff around, I discovered that in soldering on the 32 MHz tap to U405, I'd chipped a little bit of solder off and it settled under the chip, bridging a couple of pins. Removal of this fixed the clock problem, but... Strangely enough, that left me with precisely the same Glue situation as when I began. Vcc and CLK fine, output clocks fine, no vsync, no hsync, no running of diag software. Argh!

I had one more new Glue chip, and decided I'll swap it in, just to see if somehow my solder bridge had killed the new Glue. I'm getting more SMT practice than anticipated here, but at least I'm getting pretty good at it now, so swapping out the Glue wasn't difficult. Same symptoms on the new new Glue. In fact, things were even closer to the original symptoms at this point, because I was sometimes getting sync briefly on powerup, only to lose it fairly quickly, and was getting instruction fetch errors in the diag software when it could be convinced to run at all.

So this morning I checked all my Glue solders, no problems, no change. Then I moved over to my booster solders, found a few I wasn't entirely happy with, although nothing that actually looked bad. As long as I was in the neighbourhood, I reflowed the TOS switcher board solders as well (and a few of those actually did look iffy), and that left me with the above situation. Took a couple of tries to boot, and a couple of tries to get GEMBench to run, but eventually it ran. This leads me to believe that the original Glue may have been fine all along. Possibly the whole problem was the TOS switcher board, although it is odd that it ran perfectly stable after swapping the Glue and before installing the booster. And it comes as something of a surprise that the Glue does not necessarily produce sync, even if it's working fine.

Like I said, I'll pop in some different RAM, which was my plan anyway, since this machine still has only 1 MB (though I don't think it's original). Maybe inspect the solders one more time and see if I missed anything. But definitely in a better place than yesterday!

[exxos]

Done the reset circuit fixes ? Made sure you having got a "S" version buffer ?

ROM sockets on the STE are iffy, best to remove any sockets in fact to rule out problems.

[derkom]

Done the reset circuit fixes ?

Erm, no? I wasn't aware of anything necessary on the reset circuit on the STE. Point me in the right direction?

Made sure you having got a "S" version buffer ?

Wait, S or F? Your booster page says, "some STE's may have a 74S257chip for U405. This chip does not output correct TTL voltages to drive the booster. As such the machine will likely be unstable or not boot. This IC should be replaced with a 74F257 IC." Both my STEs have a 74F257. Which one is actually the desired one?

ROM sockets on the STE are iffy, best to remove any sockets in fact to rule out problems.

No sockets here. Switcher is soldered.

[exxos]

The 74F257 is the ones you need.

Reset stuff here https://www.exxosforum.co.uk/forum/viewt ... =17&t=2175

BTW is your blitter integrated or external ?

[derkom]

Reset stuff here https://www.exxosforum.co.uk/forum/viewt ... =17&t=2175

BTW is your blitter integrated or external ?

Ah, thanks. Will check into that.

Blitter is integrated. I know you mentioned that that may require some "resistor fix". Figured I would address that in time, but there's no time like the present. :)

[exxos]

Blitter is integrated. I know you mentioned that that may require some "resistor fix". Figured I would address that in time, but there's no time like the present. :)

I'm waiting on @PhilC to get back to me with testing internal and external blitter fixes currently.

Also note you need to likely do DMA fixes as well. https://www.exxosforum.co.uk/forum/viewt ... =17&t=1585