25MHz cube motherboard recap and vram replacement

Started by Nitro, June 11, 2023, 05:41:19 PM

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Nitro

I recapped a couple of 25MHz cube motherboards recently and replaced a physically damaged video ram chip as well. I picked up this inexpensive tweezer soldering iron and it worked like a champ to desolder the SMD caps.

tweezer_iron.jpg
https://www.amazon.com/dp/B01M2YHJAB

The board that required a new vram chip was physically damaged during shipment years ago. Replacing the video ram chip required a bit more work to desolder than the caps did.

before.jpg

during.jpg 

The board cleaned up nice with no lifted pads, so that was good. The new vram chip soldered in nicely, and I was able to reflow the solder on the top side with a fine-tipped iron.

vram.jpg

after.jpg

When I went to test boot the board I was met with a black screen, and the keyboard power key wouldn't shut the cube down. It sat for a few days until it occurred to me to swap the v66 EPROM chip with one from a known good board. The cube then booted up and ran normally. Whew. The recap of the second board was successful as well.

If you need replacement video ram chips for your NeXT then these are the ones I used:

Mitsubishi Electric 24-PIN 262,144-Bit Dual Port DRAM M5M4C264AL - 17PC (1 TUBE)
https://www.ebay.com/itm/272703366698

I also had good luck with MG Chemicals #8341 soldering flux paste.
https://mgchemicals.com/products/soldering-supplies/soldering-flux/soldering-flux-paste/
Nitro

pTeK

Excellent work Nitro, To the right of the RAM chips where the blob of solder is, what 28 PIN CHIP and HEADER pins go there? Oscilator, GAL, FPGA??

How many layers is the NeXT board? That NeXT promotional video, The machine that builds the machines is very inspirational, it's a shame it can't be digitized at a higher resolution.

barcher174

The missing chip is a video buffer. It was populated by special order for units that included a card for use with projection equipment for classrooms and demos.

Nitro

Quote from: pTeK on June 12, 2023, 01:52:59 PMExcellent work Nitro, To the right of the RAM chips where the blob of solder is, what 28 PIN CHIP and HEADER pins go there? Oscilator, GAL, FPGA??

How many layers is the NeXT board? That NeXT promotional video, The machine that builds the machines is very inspirational, it's a shame it can't be digitized at a higher resolution.

Thanks. I haven't seen a high quality version of the video, unfortunately. Maybe Apple has a high definition version stored in a vault somewhere; that would be cool.
Nitro

pTeK

Quote from: Nitro on June 13, 2023, 10:26:19 AMThanks. I haven't seen a high quality version of the video, unfortunately. Maybe Apple has a high definition version stored in a vault somewhere; that would be cool.
Yeah that's what pisses me off about that $trillion dollar company, but I guess that is why they are a $trillion dollar company they don't spend $$ on archiving their old stuff.

I remember seeing a 480p version of Steve Jobs demoing NeXT 3.x and it was better quality then all the other youtube versions, sadly I can no longer find the link.

Quote from: barcher174 on June 12, 2023, 02:56:33 PMThe missing chip is a video buffer. It was populated by special order for units that included a card for use with projection equipment for classrooms and demos.
Thanks for that @barcher174

gtnicol

Quote from: barcher174 on June 12, 2023, 02:56:33 PMThe missing chip is a video buffer. It was populated by special order for units that included a card for use with projection equipment for classrooms and demos.

I had a couple of those boards. It'd be interesting to see one work.