Recent content by rodders

To continue with testing I've lashed up an alternative PSU with a cleaner output. After much cleaning, examining and testing I established that the ROM select line was not being activated. This line goes through jumper W1 which disables the ROMs when a SIMMROM is used. By removing the jumper I...

This is what 5V looks like on the cheap PSU: that can't be good. I've tried another, PSU with much cleaner voltages. The clock signals look much better but still no chime, its just not booting. I've checked a few address and data lines but there's nothing happening. The main chips do warm up a...

Checked reset values at various points, all were high (inactive). The spikes in the DC voltages are coming from the cheap PSU I used. The scope shows spikes at 22kHz of about 2V p-p. I'm guessing this is seriously going to mess up the clocks which could explain why its not booting up. I've dug...

Checked voltages all over the board and I'm getting 5.02v everywhere. I had a few problems checking the clocks as my scope was coming up with som weird values. However, setting the ranges appropriately and calculating manually all 4 clocks seem about right. The problem seems to be noise on the...

I do get a thump through the speaker when I switch on but I suppose the sound chips could have a problem. I have hooked up the Apple Colour Monitor that came with it but I don't know if it works. There is nothing on the screen but that could be because its faulty or out of adjustment. I need to...

1. No, no chimes at all 2. I haven't checked out the reset yet. I'm working through Voltages, Clocks, Reset next.

Another step forward, I buzzed out the stop part of the startup circuit and found an open connection between pins 2 and 8 of the 74HC132 so the SR latch wasn't working. It was a bad solder joint between pin 8 and its pad. Re-soldering it means the power stays on now. It doesn't get much further...

Thanks guys, I'll have a probe around. I've done lots of repairs so not surprising it didn't work first time. Still trying to get my head around how the startup circuit works. In particular, does it hold the PS-ON line high all the time it's on or is it a momentary thing? I'm assuming the...

Well, I finally plucked up the courage to switch the thing on. Thankfully no magic smoke but this is all I got: Its clearly trying to start but failing and trying again. I'm guessing that its not even getting into the POST. If anyone has had a similar experience and knows where to start looking...

Hmm, when testing I found that the soft start didn't work. It turns out that the optocoupler design I used has pins 3 and 4 labelled the wrong way round. I feel a bodge wire coming on...

Finally got a usable PCB for my interface board. The Kicad footprint for the 24 pin ATX socket follows the Molex spec. and has a larger pitch between the rows of pins on the PCB side than the plug side whereas the Chinese copies that I have are the same (simpler to manufacture I guess). As a...

Restoration proceeds in https://68kmla.org/bb/index.php?threads/restoring-my-iicx.48705/

I have one question. Some people claim this computer won't start without the PRAM battery, is this correct?

Well, the new UV torch arrived but it was pretty pathetic and I had trouble getting the solder resist ink to cure. I bit the bullet and bought a more powerful (10W) one which had good reviews. I still struggled with curing until I applied a little heat with my hot air station at around 270C...

Well, I started by scraping back any traces that looked discoloured because something nasty had got under the solder resist.In many cases the trace has not been eaten away, at least not completely, so I tinned the trace to beef it up a bit so they didn't fail later on. In some places the trace...