forums.nabu.ca

Is "NABU Recovery Operations and Hacks" where general hardware questions should go? I didn't see another forum section for this.

Anyway, I've experienced some of the same issues with out of spec video. The Nabu doesn't work when connected through my Extron switcher and composite converter which is where all my other retro hardware goes through. The Extron switcher just plain refuses to pass the signal and the Extron IN1502 will take the signal but with tearing across the top. I also have a RetroTink Pro that handles the video just fine as well as an old Sony monitor which also does the trick but some of my other composite video gear doesn't like the signal either. I saw on the John's Basement video that he was able to use an inline resistor to get it back into spec and someone else recommended a diode. Any consensus as to what the best approach is?

Funny enough, I have the same problem with my video capture. Well, my video capture needs HDMI, so my main issue was with the composite to HDMI converter. Sometimes it would work and lock into the signal, but 90% of the time, it wouldn't. I tried adding a kabillion different ohm resistors to lower the db, but nothing worked. I'm not sure if the DB level of the signal is causing the issue with the HDMI converter or the signal itself. For example, I should scope it compared to a Coleco to see the difference.

Let me know how it compares to the Coleco. A lot of 9918a-based designs seem to have different approaches to the DC level of the 9918’s COMVID output and unfortunately the Nabu seems have its own approach. I’m getting a good picture on a Sony PVM-5041Q monitor and a reasonably ok HDMI output from the RetroTink but definitely isn’t the best quality I’ve seen from a 9918 system.

I put my scope on it and you can see the same issue that the John's Basement video shows, the DC offset is like 1.2V. This shouldn't be the biggest problem but it does seem to mess up certain capture devices as wells as composite to HDMI adapters.

I don't think a resistor in series is the solution - I think a proper voltage divider is necessary

Glad to hear I'm not the only one with this issue. I'll refrain from buying a second NABU in hopes of getting one with better composite output.

fastrobplus wrote: ↑Sun Apr 23, 2023 7:04 pm Glad to hear I'm not the only one with this issue. I'll refrain from buying a second NABU in hopes of getting one with better composite output.

They don't make NABU computers anymore. The ones that are for sale right now are from the early 1980's.

Yes but there was some speculation in those YouTube comments that each nabu may be displaying video slightly differently. The person who used an inline resistor seems to have had different results that I did trying the same fix. I get a pulsing background on one monitor and a clear but greyscale image on another monitor.

I did just try to use a "TinyComp" from https://jcm-1.com/ to pickup the video signal prior to the RF modulator and fabricate a new composite signal to a new RCA jack and amazingly this worked great! I had beautiful blue and white video and was ready to call it a success but after about 5 minutes it degraded and stopped outputting, so it's back to square one.

First power on for my Nabu and looks like I have a bad DRAM chip, U22 according to the Nabu PC Diagnostic manual by Rudy’s Retro Intel. Thanks Rudy for putting this together. I probed all the other Video DRAM chips and all look OK except U22, at lease they are output some data on Q, U22's Q is always low..

Tracking down some 4116 DRAM in Toronto, or ordering on line. Then will remove & replace U22 with socket & working chip.

Any recommendations best methods to remove board and replace this part?

Oh that's too bad. You know what? I needed a solder sucker at my cabin last summer. I found this on Amazon:

I have to say, it's pretty awesome. I actually really enjoy using it and for the price, you can't go wrong. So if you don't have one of these in your arsenal, i'd recommend it!