johndias

Finally got back to this. So, I tested the A101 on both boards I have. Both of them give a high on the logic probe, where I should be reading pulse on pins 30 and 32. 30 is CS0 and 32 is R/W. I also probed pin 24 after running CLOAD... no pulse. Does this mean the POKEY is bad?

Ah, I did have this issue yesterday when I unplugged/replugged the FTDI into my laptop. But I just deleted the unknown device and it recovered. I'll check into this more - nobody else on Amazon reported issues with this FTDI breakout, but I guess it could still have gotten a fake. So, if I were to scope the SIO port and the POKEY, what would indicate a good connection and chip?

No matter what I do, I can't get anything to show except "MEMO PAD" Can't even get the thing to boot from the Atari DOS folder if I mount it. I also tried on another 400 I have and it's not working on that one either. I tried loading PuTTY, and I can hear some noise from the monitor speaker when I press keys in the terminal session (I have UAV and the sound upgrade installed).

Hey all, I have a 400 that I have built a DIY SIO2PC connector for so I can load program files with RespeQt. I'm not having a lot of luck. I bought an FTDI board, built a "franken-cable" to pin the outputs on the FTDI to the appropriate pins on an SIO cable which I connected to the SIO port. I have continuity from the FTDI pins through to the connector. However, I am not able to load anything. RespeQt seems happy with the connection, correct COM port using CTS at 19.2K baud. However, the xex files I try to boot from don't load. Even after I reset (hard or soft) the 400. Is there a step I am missing here?

Stupid question, sorry - but for the audio output can I just use a RCA connection?

Success! Well, kind of. I bought a non-working 400 from ebay (which turned out to be working) and swapped the CPU board... color is fine. I guess the pot was the bad part? I will fiddle with it more to try and narrow it down but for now, my UAV is looking good!

Well, I've replaced the cap and broke the pot down and cleaned it with alcohol (it was just a little dirty). I tested the pot and only got 462k ohm. The result is the same, around +5.7 on the pot output. I bought another 400 from ebay and when it comes in I'll try out the CPU board to see what I can do. Very frustrating! But, thanks everyone for the help and instruction.

So as I was desoldering C305 it disintegrated on me. I'll have to replace it, but I guess it was so fragile because it was failing?

Just under +12V

OK, I see. I can't figure why I'm only getting +5.5VDC maximum. I pulled R308 and it tested at 330K OHM. However, with power the voltage out from R308 is only +5.5. Should I just replace R308?

So, this schematic matches what I am seeing. And basically I should NOT be getting +12V on the pot, but rather +5V so there's no problem there. At this point, I think the GTIA chip is bad - I'm going to see if I can find a replacement.

OK thanks, then that's the right crystal. Yep, when I turn all the way left I get 5.5v - back to the right it starts to decrease to zero when it stops. So, I think I have to trace back to my power supply. I'll pour over the schematics to see what I can see.

So, I adjusted the pot but only got some "noise" on the screen - colorful noise, but noise. When I checked, the pot only got around 5.5v if I turned it all the way in one direction. Voltage on pin 17 of the GTIA was around 5.5v. The GTIA has a part number for NTSC. I don't know how to confirm the crystal?

Rechecked the connections, and wiggles didn't change anything. I wonder... I'm attaching to a 4 pin s-video cable I had laying around. S-Video 1 - no connection 2 - ground to UAV 2 3 - Chroma on UAV 4 - Luma on UAV And I'm picking the C187 on my motherboard for color. Anything else I can check?

Never! And thanks for the help. So I was testing from the board perspective, not the CPU itself. However, it seems that I've gotten things to work somewhat (maybe by re-seating every chip I could find). The RF looked snowy on my display, so I went ahead and installed the UAV I bought recently and presto - I get video... but black and white, no color. Tonight I investigate that issue, although I'm certain I tapped the correct place on the mobo for color in. Good news is, a quick keyboard check in memo pad shows all keys working.

I get a black screen, but I do hear key clicks from the internal speaker. I was following these pages from the field manual (attached)

Thanks to both of you for the help. @rybags it appears I have the "legacy" CPU, so I'll follow your suggestion on scoping the SYNC pin. @ACML no worries, never hurts to state the obvious when helping someone troubleshoot! But, I did re-seat the CPU board chips. However, I didn't re-seat the chips on the memory board so I will try that as well.

Hi all, I am a complete newbie to this hobby, so forgive me if I missed the obvious. I think I've done my homework but you can tell me if not! I am following the troubleshooting in the field service manual, my workflow begins with a system that powers up but has no video. The power has tested fine on the PSU board, so now I'm on to the CPU. Here I ran into a test failure and I'm not sure what to do. The docs have me checking clock circuit and I am not getting any waveform for pin 8 of Z302. From the docs, it just says it will tell me which component is failing but I can't see how to figure that out. Any ideas? Thanks in advance.