Recent content by Dwight Elvey

The I/O ports are relatively easy to talk to thru the monitor and a minimal of code. Debugging anything there should be relatively easy. There are not that many things that could have shorted other than the wires at the connectors. Dwight

If you put sockets on the board,make sure to use an ohmmeter to make sure both the top of the board and the bottom of the board traces make good contact to the socket. I like to use machine-pin sockets because it is easier to solder the top side if the feed thru is broken in the repair. Dave is...

Hi Do you have an oscilloscope? That will help quite a bit. A logic probe can be used but a volt meter would be quite restrictive. The diagnostic board is quite simple and could easily be put on a hand wired vector type board. There area couple sections of the EPROM that are intended to be used...

It is like with a sharp knife. When you notice it starts to fall, you move quickly out of the way, rather than reach out to catch it. It is a lesson that is learned early on.

What can make it more confusing is the timing diagrams. Unless the diagram shows which level is VCC, one doesn't know if a one is up or down for PMOS. Is up a one or is down a one. I find the only way to tell is to look at a schematic with a TTL involved. Dwight

love it !

I've still not taken the time to debug address error on my SYM4-01. I need to do that before reading the AD542 EPROM. On a separate subject, I was looking at the description of the stack in the instruction manual on bitsavers. I was looking at the description of the stack in the programmers...

Then you know that a ST-506 drive is only 5megs in size. That is why I asked. A drive with ST-506 compatible interface might go to around 100 megs as I recall ( not really important number though ). I have a real ST-506 drive that I used with my Forth computer. These drives have a killer issue...

What I'd like to see is a soldering iron that turned the heat down a little when put in the holder. When working on projects, if I forget to turn down the heat, the tip looses its nice tinned surface to oxides. I see on the web people using oxidized tips to solder with and wonder were they...

Hi I'm just curious. Are you looking for a real ST-506 drive or just a ST-506 compatible drive? Dwight

I doubt it used 1702s, They only made them for a short time and not while the 8080 was made. I'd think it only did 1702As. The programmer card looks like a typical programmer for 1702As. There are a number of one shots at the bottom of the picture for the programming pulses. The 2102 RAM chips...

I doubt it has anything to do with the charger unless it was generating spikes. I doubt it is the video chip. What I was talking about is the TFT/LCD driver chip. It is often part of the screen but I've never looked at your machine. The fading is the result of the DC bias on the signal going to...

I assume you have an LCD screen. The problem is the pulses to the screen have a DC component. Don't run it to long like this or it will damage the screen. I'm not sure how your particular screen maintains the AC balance. As I recall most driver chips do that internally. It is possible that some...

The big T03 looking ic's are the drives for the stepper you might check some ofthe voltages around them. The stepper motor with nothing happening should have grounds for each phase step. If you don't see any of the phases with 24V on a meter the stepper motor has an open.You can look at IC 1B to...

PolyPhase format requires a good quality tape machine as it uses timing of phase shifts to create and restore the data. When those phase shifts happen require the proper phase delay over a relatively large portion of the audio spectrum. The Byte format just requires a couple of pure tones to be...