IBM PCJr

[Lutiana]

Both of my PCjr machines have the socketed Intel 8088 procs and I want to switch them out for V20s.

Would this work? And it is the optimal part to use?

If that is not the right part can someone give me a part number that would work?

Thanks in advance. :D

 

[Maverick1978]

Check Mike Brutman's PCJr page - while I don't recall him having a link to a specific part number, he has the info about the NEC V20 being what you want in the Jr if you're looking for a processor upgrade.

Incidentally, you'll want the 5mhz clock upgrade if you're running the Jr with the standard clock crystal and timing. You've linked to the 8mhz part. FWIW, an ebay seller has the 5mhz part you need (search for nec v20), but he's rather expensive ($26 shipped). I'd Google the p/n D70108D-5 and see what you come up with (Jameco doesn't appear to carry anything but the 8mhz chip)

 

[ibmapc]

Actually, the 8mhz V20 will work fine at the Jr's 4.77mhz. The other way around would be a problem(Trying to run a slower processor in at a faster clock speed than it's rated for). So, yes that part should work perfectly.

 

[Lutiana]

Actually, the 8mhz V20 will work fine at the Jr's 4.77mhz. The other way around would be a problem(Trying to run a slower processor in at a faster clock speed than it's rated for). So, yes that part should work perfectly.

Awesome. Thanks, I'll probably order 2 next week.

 

[Chuck(G)]

Actually, the 8mhz V20 will work fine at the Jr's 4.77mhz. The other way around would be a problem(Trying to run a slower processor in at a faster clock speed than it's rated for). So, yes that part should work perfectly.

V20s are funny that way. I'm currently running at least one 5 MHz V20 at 8 MHz with no problems, heating or otherwise. It's in a CerDIP package.

That's the funny thing with a lot of early CMOS. As production ramped up, the yields got better, the labeling for the lower speeds would simply be apportioned out according to demand (there are some service manuals that specify the lower speed and some service depots wouldn't order the higher-speed part just out of pure stubbornness). You can see that with early 90's 41256-type DRAMs. After awhile, some manufacturers just quit putting speed labeling on the parts, since every chip that came off the line would pass the 70 or 80 nsec. speed test.

However, on earlier chip runs, that's not safe, as the faster chips are removed from the production stream. Buying a bunch of lower-speed chips in hopes of finding one that passes for a higher-speed version is not a good idea.

Same for stuff like carbon composition resistors. Buying a bunch of 10% devices in hope of finding a pile of 5% qualifiers will almost never work--they've already been sieved out of the production stream and labeled as such.