Embarking on an Altair 8800C build

[BillO]

From what I have heard there is no standard fix. Do you have a 2ch. oscilloscope? It would be handy if you posted a picture of your two clock phases with voltages and relative timings.

[TheoAU]

You have to tweak each system individually. In my case, I got lucky and simply swapping out the 8080a (even though both are genuine Intel chips) was enough to bring the system into spec and eliminate the front panel errors I had been getting.

Thanks Tom, that's good to know. Good idea about trying other 8080a CPU's. I have two or three spares that I can try, including an old ceramic one. I've read in other threads to view the clock issue you need an oscilloscope, which I don't have. But this would be a great excuse to get one.

[TheoAU]

From what I have heard there is no standard fix. Do you have a 2ch. oscilloscope? It would be handy if you posted a picture of your two clock phases with voltages and relative timings.

No, I don't have a oscilloscope but it'd be great to get one. If anyone has any recommendations on good hobbyist oscilloscope send them my way.

[KenF]

https://www.amazon.com/gp/product/B08L3 ... UTF8&psc=1
This is a satisfactory scope for a hobbyist. I got it for the portability as a second device. It certainly doesn't have the capabilities of my Techtronix bench oscilloscope, but it is a quarter of the price. Plenty fast enough and more for any 8-bit processor. Digital of course. Two channel.

However...
I use this far more often than a scope..
https://www.amazon.com/Inno-Maker-Analy ... 313&sr=1-4
16 channels and again, far faster than any older computer. USB connected and works on any OS. Really good software comes with it. And only 80 bucks.

Ken

[TheoAU]

https://www.amazon.com/gp/product/B08L3FRKYF/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
This is a satisfactory scope for a hobbyist. I got it for the portability as a second device. It certainly doesn't have the capabilities of my Techtronix bench oscilloscope, but it is a quarter of the price. Plenty fast enough and more for any 8-bit processor. Digital of course. Two channel.

However...
I use this far more often than a scope..
https://www.amazon.com/Inno-Maker-Analy ... 313&sr=1-4
16 channels and again, far faster than any older computer. USB connected and works on any OS. Really good software comes with it. And only 80 bucks.

Ken

Thanks for the suggestions Ken, they look good.

[AltairClone]

Theo,

Yes, you'll need a scope to properly adjust the CPU clock. On the CPU board, connect channel A to IC-Q pin 13 (phi 1) and channel B to IC-Q pin 5 (phi 2). Set the vertical scale to 1v/div and have the two signals at the same vertical position on the screen so they overlap each other. Set the time scale to see about one full cycle across the display. Post a clear screen shot of that.

Mike

[BillO]

https://www.amazon.com/gp/product/B08L3FRKYF/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
This is a satisfactory scope for a hobbyist. I got it for the portability as a second device. It certainly doesn't have the capabilities of my Techtronix bench oscilloscope, but it is a quarter of the price. Plenty fast enough and more for any 8-bit processor. Digital of course. Two channel.

However...
I use this far more often than a scope..
https://www.amazon.com/Inno-Maker-Analy ... 313&sr=1-4
16 channels and again, far faster than any older computer. USB connected and works on any OS. Really good software comes with it. And only 80 bucks.

Ken

The logic analyzer will not give you any idea how clean your signals are, and unless they can allow for the particulars of the logic family under test (NMOS, HMOS, TTL, CMOS, etc.. which all treat what level "0" and "1" are differently) can give you significantly erroneous timings. LAs that do all that run a pretty penny. Lower cost ones are great for decoding serial protocols though. That one look pretty good though. While you need to enter thresholds manually it does have that ability. Cool.

[BillO]

If anyone has any recommendations on good hobbyist oscilloscope send them my way.

Depends on your budget, but something like a Hantek 6074BC USB scope is very useful. For a little more you might consider the Hantek DSO2D15 which includes a signal generator and the ability to decode serial protocols. Then up the scale a little further you have the Siglent SDS1104X-E or even the SDS1204X-E .. still under $1000. I can vouch personally for the Hantek 6074BE and teh Siglent SDS1204X-E both of which I have and both do a great job.

[TheoAU]

Theo,

Yes, you'll need a scope to properly adjust the CPU clock. On the CPU board, connect channel A to IC-Q pin 13 (phi 1) and channel B to IC-Q pin 5 (phi 2). Set the vertical scale to 1v/div and have the two signals at the same vertical position on the screen so they overlap each other. Set the time scale to see about one full cycle across the display. Post a clear screen shot of that.

Mike

Thanks Mike, these are exactly the sort of directions I need. I'll get my hands on a scope and report back.

Luckily this is not an urgent issue. I've been using my new machine over the last couple of days and with the current configration which resolves the 882SIOJP issue, it's proving to be consistent and reliable.

[TheoAU]

If anyone has any recommendations on good hobbyist oscilloscope send them my way.

Depends on your budget, but something like a Hantek 6074BE USB scope is very useful. For a little more you might consider the Hantek DSO2D15 which includes a signal generator and the ability to decode serial protocols. Then up the scale a little further you have the Siglent SDS1104X-E or even the SDS1204X-E .. still under $1000. I can vouch personally for the Hantek 6074BE and teh Siglent SDS1204X-E both of which I have and both do a great job.

Thanks BillO, I'll look into those models.