Search results

First timer here also. Awesome show all around. Agree that Ruud and Birt's presentations were very informative - those were the ones I had in mind when I signed up. I'd seen Birt's retrobriting analysis on youtube and appreciated the attention to detail, so he was the main reason I signed...

The crystal tests ok. Tested by building an AD9850-based signal generator and pushing 9mz and 10mhz through the 10mhz crystal. Output jumps when I hit the correct frequency. Actually found the frequency to be 10.001 Mhz Attached imaged show a red trace which is the output from the signal...

I don't have any spare crystals lying around, but ordered a pack of cheap crystals in different frequencies, they will be here in a few days. The two capacitors tested OK on the LCR meter, 20.5 pF, which is close enough given the rating of 20 pF +/- 5%. I am putting together a cheap signal...

Confirmed that there is no oscillation on the XTAL pins of the 80c39. They read 2v and 1v, flat. On powerup they go direct to those readings with no delay, and stay there. The keyboard does not work, even when I got to the 'world map' screen while I had the oscilloscope hooked up, no...

I appreciate your assistance! So, given that the schematic and board don't match in this case, my confusion on inductor vs crystal was understandable, so I don't feel quite so silly. :) However this inductor/crystal is the first inconsistency I have noted in the schematic compared to my...

You are correct, I need to look closer - the concept is clearly not as simple as I had thought.

That is the chip. Y2 is an inductor? I thought it was a crystal oscillator... In my mind the difference was that a "clock signal" is what I would call something that had more of a square wave, and the "crystal oscillator" was the silver component (usually with a frequency printed on it)...

Quick question... On the 80c39 ("Keyboard Controller" in the schematics) the two XTAL pins go to either side of a crystal oscillator, then both pins go to ground through big capacitors. I don't read a clock signal there, and the two capacitors appear to be open don't go to ground. I'm...

I got the thing to sort of boot... Long story short... Attaching my LA to the 8 data pins on the PPI resulted in a change to the bootup behavior. Previously I would get a "Testing Memory" message for a few seconds, then the message would be replaced with a flashing black cursor and the CPU...

Continuing this diagnosis, I've found a couple of interesting things using the LA on the 8088 pins. The 8088 is running in max mode, so I can use the state pins S0/S1/S2 to tell the difference between IO Write, Mem Read etc. One of those states is "Halt". That's where we get to right as all...

Ah! I call them "factory bodges". There are a couple, I'll have to compare the diagram with them to see if they affect the screen. For now I'm trying to get a clear read of BIOS ROM addresses that are being read. I'm seeing addresses bring read that are in the copyright message, so that...

I don't have the RGB card, is that what you mean by a 'barnacle' (like the memory and modem cards?)

So, your character rom versus my character rom... They are the same, except for one small detail... :) (No change to the boot failure behavior, but it's cool to find it's just an inverted rom. I wonder - could we burn both onto a 27C512 (one rom in the lower half, the other rom in the...

I appreciate you taking the time to scan that for me! If you are scanning at 1Mhz you may be missing data or getting a harmonic/resonance effect. I have been scanning at 100mhz and I find that to be too fast because I get strange results where some pins change before other pins. The bet scan...

I got an immediate message saying that there was an error at 0000:0000 bit 0, so that seems to work. I put the memory board back inn place and gave it 30 seconds. The "Testing memory" message lasts about 10 seconds, then soon after the message disappears the traces stop showing activity. I'm...

Cool, I'll try that.

Will try, stand by. Also I'm looking to see if I can use a 27/256 eprom in place of the 57/256 character rom.

Interesting.... Your character rom and mine are actually fundamentally the same, but there's something funky going on. A quick glance gave me the impression that my rom has many of the bits inverted. Example of first 6 bytes: Mine: FF 81 81 FF FF C7: 11111111 10000001 10000001...

Sure, good idea, that should be easy enough. I'll see what blank eproms I have.

There were some minor differences I believe. I'll disassemble your rom and see what the differences are.