Overclocking the awesome little PCjr. + Repair + testing faster RAM chips
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- Опубліковано 1 гру 2023
- Skinny Sprint v2. Overclocking IBM PC, XT, Portable, and PCjr.
PCB Prototype the Easy Way. Full feature custom PCB prototype service. www.pcbway.com/
Gerbers and BOM here: github.com/epictronics/Skinny...
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Tools I regularly use
DeoxIT D5 Contact Cleaner
Hanstar 861DW Rework Station
Pro'sKit SS-331 Desoldering Station
UNI-T UT61E Auto Ranging Multimeter
UNI-T UT890D Manual Ranging Multimeter
MESR-100 mk2 ESR meeter
PINECIL Soldering Iron
PinePowerPSU
TS-100 Soldering Iron
AMTECH NC-559-ASM Flux
Kester 951 Flux pen
MaAnt Grinding Pen
Multicore 60/40. 0.38mm and 0.5mm solder
TL866 II Plus Programmer
RIGOL DHO800 70MHz four-channel digital scope
Tektronix 2246A 100 MHz four-channel analog scope
InfiRay P2 Pro Thermal Camera
PCBs from PCBWay.com :)
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patreon.com/Epictronics
Join me on Twitter: / epictronics1
Music by Karl Casey @ White Bat Audio - Наука та технологія
I read something interesting in a data sheet after making this video. I think I know why we couldn't go faster. Parts ordered, stay tuned!
Support me on patreon.com/Epictronics
Join me on Twitter: twitter.com/epictronics1
Gerbers and BOM here: github.com/epictronics/Skinny-Sprint
Looking forward to it!
Does that mean I should still hold off a little bit longer before I order PCBs for my IBM 5155 or are the Gerbers "finalized"? =D
@@cloakedalien PCBs are fine, we are going to swap some chips next
Awesome video.Have you got my promo code of microscope?
Now this is real overclocking!
Enjoy Egypt Mr Epictronics, I too have always been fascinated by the pyramids. I mean who isn't I suppose.
Thanks!, I went inside the Great Pyramid today. It was boiling hot in there, It's like a huge sauna!
May need to change the delay lines used for RAS/CAS strobe. Increasing the clock speed means that the delay lines may have too much delay.
I'll check, thanks
ctrl + alt + insert is your internal self test on the PCjr
Nice job on the redesign; I’m looking forward to trying the board. Have fun on your trip and aafe travels!
Thanks!
Nice! I always find it enjoyable to see how far these older machines can be pushed. Especially the PCjr such an adorable little machine that somehow came out of Big Blue.
Thanks! It's very different from other IBMs for sure. I really like this little machine :)
15:30 The way to fix it is to simply sand the legs of all the chips with 400-grit sandpaper. That will remove any corrosion and old solder. For larger amounts of solder use your powered desoldering tool and put the leg inside the nozzle and suck all the solder off the leg.
In hindsight, I should have cleaned all those chips with the desoldering gun for sure!
The glitch around 14:00 with the random characters is likely because you had a light shining brightly picked up by the front of the system, which was causing random IR keyboard signals. This happens all the time when I try to shoot video of a PCjr, you need to have the keyboard cable attached (or take the keyboard IR module out) to work around this :-D
There was a speedup product for the PCjr that ran the CPU at 9.54MHz, and I think it did that by only changing the divider and not speeding up the entire system. Is that possible with what you're testing?
Lol I have an old late 70s TV with an infrared protocol that basically transmits ultrasound frequencies over IR, so no codes, just the frequency alone determines what button has been pressed.
When I had a CFL installed as a ceiling light, when the light is switched on, the TV would switch to channel 6, then as the CFL warmed up, channel 7 and then 8.
Thanks, I didn't know it could cause that issue. I'll bring out the kb kable for the next attempt. Thanks! Yes, the Skinny Sprint only changes the CPU speed. The rest of the system is unaffected. I think I know what the bottleneck is now. Parts ordered, stay tuned!
Would that bottleneck also affect the 5155?
@@TheSimTetuChannel Yes, all four machines
Always place the values of the components somewhere on the PCB.
Now you need a separate document to know in the future what components you need to use.
Yes, that would be a nice addition to these boards
Great job you did. Keep up the good work. Greetings from Steven from the Netherlands
Thanks!
"Obviously"
Haha, love this dude.
You could program a RAM test in BASIC just using PEEK and POKE or whatever the PC Jr uses. Would be slow of course, but you'd get a consistent test, using 100% of the actual hardware, in-situ. Just poke in 0 to each address, then read back. Then 255, then read back. Then, maybe, 1, 2, 4, 8, etc one bit at a time. Then after that every value from 0 to 255. Repeat the whole test over once it's done, set it to print results to screen, or maybe printer or floppy, so you'd have a record of how far it got before it failed. Then go to bed!
I suggest this order because hopefully it will flag an error quickly if there's anything wrong, the tests ought to fail more quickly with a fault, than just POKEing 1, 2, 3, 4 would.
I imagine when you wake up to sand and sunlight every day, mixing in a few pyramids is a welcome sight?
Absolutely, I had a look inside the Great Pyramid today. It's weird and awesome
Enjoy your trip to the pyramids. Remember, it wasn't the Egyptians that were bored and built them. It was aliens. 🤣🤣🤣
And they used diamond core drills to make holes because lasers would have scared those primitive Egyptians 😉
Ancient Egyptians; the current ones can barely build a shack.
Amazing video again thank you again
Thanks!
The white pixels are, I think, RAM contention. When the CPU wants to access video RAM, it gets priority. So if the video circuit is trying to draw a pixel but can't access the RAM, it just draws it white for that video frame. It's a widely-known glitch with CGA. It has no permanent effect, nor does it effect other parts of the machine. If it were me I'd have made it draw black instead so it's less noticable. Programmers would get around it by checking for the CGA's vertical blank, and only writing to screen RAM then. Perhaps video RAM in the PC Jr is different from the standard PC and maybe shares the main RAM chips?
Other computers of the time would usually give the graphics the priority and halt the CPU for a while, but IBM didn't do that. Perhaps cos there's so much other stuff on the motherboard. For example I believe the infra-red decoding for the keyboard is done in software. Which is idiotic. Saved them a few cents on an IR decoder chip but means the CPU is interrupted at high priority every time you press a key, and if it misses a pulse no keypress happens, with no mechanism to ask the keyboard to repeat. Since the keyboard is send-only and the PC Jr receive-only, they don't have the necessary components to do the other way round.
It's likely something they could have programmed into a little microcontroller like the one that receives keyboard signals on ordinary PCs with wired keyboards. They use a serial signal with a little programmed chip that decodes it for the CPU to read when it wants to. I'm sure they could have done both and it wouldn't have cost more, maybe a couple of pennies for a slightly faster microcontroller, if they even needed one.
Regardless, the keyboard is bone-headed. But that's likely why the CPU needs priority access over everything. The same thing happens with CGA on a normal PC but that's apparently for some other reason. I suppose because IBM don't know what cards a user will have installed, they can't have anything pausing the CPU's RAM access when there might be some card that can't wait around for it.
Thanks, yes, one of the quirky things with the PCjr is that it shares the RAM with the graphics. I think there is software that allocates RAM and should improve things. I have yet to look into that.
the pcjr supports infrared keyboards, right? i wonder if the random keyboard inputs could've been due to something just happening to put out ir light at the right angle to interfere with it
Yes, that is very likely. I will do the next test with the KB cable, thanks
33:22 so many (music) Keyboards! Retro Synths? Korg M1? SY99?
Yes, I'm a sucker for 1980s synths :) Got the usual suspects
@@Epictronics1 Late 80s, 90s, and early 2000s synths do it for me, too. I've got a STACK of Roland ROMplers, some Korg, Yamaha, Ensoniq, Kurzweil.. I just love them.
I think the ISA interface was designed to run at a max of 8 MHz. So this result is expected.
I didn't know it could do even 8MHz. With the Skinny Sprint, it runs at 4.77
@@Epictronics1 Other chips may limit it, but in later ISA designs 8 MHz is the standard rate. Some later ones will run at 10, but the inserted cards also have to run at the faster speed.
The 8Mhz ISA limit wasn't established until later AT machines as people realized stability would be impacted by ever-increasing clock speeds. The peripherals on the ISA bus of a PCJr weren't designed with 8MHz in mind and probably wouldn't appreciate being driven that hard.
interesting enough, before the end of the ice age the nile valley and a lot of that desert didn't exist or was much smaller. it's been established that it was basically jungle like there. then with the end of the ice age, there area underwent rapid desertification. there's also been proof that both the pyramids and sphinx are much older than most thought. however the egyptian government has buried a lot of information about it.
You say buried, but maybe it's just desertification of history. ;-)
I'll give an insanely "short" tldr on the pyramids and why they exist etc,
1. There is only so many ways you can "stack rocks" and have it be stable, triangles are strong. If you look at modern structures (large or important ones) they will have triangles in them like trusses.
2. Egypt during the era of the pyramids being built was a very different climate, a lot less deserts in the sahara region. From memory, so take with a grain of salt, one of the hypothesis of why the bronze age collapsed was due to massive climate change, droughts, famines and the "sea people".
3. One main reason for pyramids being built, religious reasons, honestly a good chunk of early contructions are or could be built for religious reasons.
People of the past were not stupid, infact its a myth that people of modern times, all throughout history, say to others and themselves to feel superior and then it becomes "accepted fact".
Can check out actifactually speaking, miniminuteman for some info on some of that area, actifactually does moremiddle east stuff but still good. Mini does mostly debunking but can get great info
There was likely still some flux on the pins of those chips. If i were you I would want to remove any old solder with solder wick and clean the pins up with isopropyl alcohol.
Very possible indeed. I should have cleaned them with the desoldering gun
Great vid. But I think you forgot to filter out the crt noise during commodore scenes. My ears are bleeding...
You know, if you sit in front of a CRT for hours at a time for years, you start to get used to it.
@@nickwallette6201, well, i did. So much that i couldn't even sleep without having at least one CRT running in the house. :D Thankfully that time has passed...
@@GigAHerZ64 LOL... :-) Well, if you were around when they were fashionable, you ought to be pretty close to the age where nature takes care of that for you. 15kHz? Stuff of make-believe! haha
The error that you are experiencing on the IBM PC 5150 is due to the fact that 64 KB of memory is not enough for your version of PC-DOS. Use DOS 3.1 or older.
I’ll check, thanks!
In the past I've seen individual turned pins that sit tight to the board, no plastic around them. Perhaps those could be used instead of sockets to get the 8284's flush with the board?
That would be a nice improvement
@@Epictronics1They are rare and expensive, don't bother. Not sure if you know what they are but they are basically the top half of a machine pin and the hole in the PCB is larger to accept the larger section of the brass pin. You can make something similar yourself. Rework the PCB to have larger holes that suit the biggest diameter of the machine pins then solder the pins in so that the thin leg section is below the PCB. Put all the loose pins into the PCB then push the whole thing into a machine pin socket to support and align it while soldering. To get the pins simply get a pin header strip and put your soldering iron into the hole and after a couple of seconds push and the brass pin will come out.
Maybe it'll take the 27mhz crystal without the RAM expander?
I didn't think to try. That being said, I think I know what the bottleneck is. Parts ordered, stay tuned!
I wonder if that would work in my IBM 5155 to give it a slight boost.
So far, it will give you a 75%! speed increase, but we're not done yet! Parts ordered, stay tuned
I always solder my sockets in starting with two opposite diagonal pins and they always come out straight and flush. Am I just lucky or is there some method to that madness?
That works well too
Check the speed of the video ram
would the round pin header fit the crystal? would make changing them easy
I tried but it wouldn't make good contact. Mayabe, my pin headers were bad
you should socket adapter for those drbuced bus 386's or 486's if it is even possible because then this pc junior might do unthinkable... run windows 95?
Not possible. Win95 needs minimum 4MB RAM and PC Jr max RAM is 512kB
@@g4z-kb7ct Anything's possible! The 8086 / 8088 can only access 1MB RAM (though there was expanded memory that paged in a block of 16K or so in the address space, if software supported it, Lotus, Intel and Microsoft created the LIM standard for it. 32MB is the limit.)
You could design a board that took one of those 486 adaptor thingies and put the RAM on board, and I suppose you'd need some of the support chips on there too. At that point you're essentially just building a separate 486 computer that drives the ISA bus, badly. You lose the meaning of why you're doing it.
You'd have to put a VGA card in too for Windows 95. It'd end up being completely alien to it's nature, and would run like shit anyway. Only worth it if someone's made you an extravagant bet, perhaps.
Be careful in Egypt, I understand crime against tourists is up this year. Last year my cousin went, and felt fairly safe, but that was because they had armed police officers with them every step of the way.
We actually had a police escort on our trip to the Kairo museum yesterday.
Why not install a socket for the crystal?
I tried with female pin headers but didn't get good contact. Could have been just bad pin headers
Did you try memory chips with faster timings?
I never thought of timings for these chips actually. I'll do some reading
Couldn't you have just soldered in pin headers for the crystal?
I tried, but it wouldn't always make good contact
@Epictronics1 were the sockets round holes?
@@jacobmckenna8661 Yes, machined pin headers
@Epictronics1 I think Adrian's Digital Basement socketed a crystal for overclocking and I remember him having a connection issue that was solved with shortening the legs
Random question but does your Profil Pic come from Gravity Falls ?
That’s what I’ve wondered as well.
Yes, It's heavilly inspired by Bill Cipher
Could this done on a Tandy 1000?
It should be doable on the original, but not on the A or HD.
@@fortmax8370 It's quite likely that there is something similar for an 8088 Tandy. I'll find out when/if I ever find a nice machine to restore
Dave Jones (EEVBlog) did a different overclocking mod on his Tandy back in the day. One of his earlier videos (EEVBlog #32) from September 2009 discusses it. I believe his mod uses an entirely different mechanism but it's been a while since I watched that video.
Why not try putting a faster rated CPU in there? You can get NEC V20s up to 16MHz, I think.
I worry about you using 2 separate clocks, which is how I understand it. Would be better if you used just the CPU clock, and then divided it down with a couple of flip-flops or a counter chip. Then stuff would be more in sync, computers weren't usually designed to run asynchronously back then, the ISA bus, the RAM, and the CPU should all be in sync. In fact they should all be at the same clock speed but if you can't get the whole system to run that fast, you could at least have a clock divided down from the CPU's clock.
The V20 is also about 20% faster than an 8088 even for the same clock speed. Some of it's instructions run in less cycles. It was a popular mod back in the day to swap in a V20 or V30 (the 16-bit bus replacement for the 8086) for your CPU.
You could experiment with different crystals and different dividers. A counter chip would be ideal actually, if it can run at the required speed. So you'd have 1/2 1/3 1/4 and whatever other speeds you wanted. Use a pin header with jumpers to connect the desired pin.
I’m using a 10MHz V20. I didn’t think there might be an issue with two crystals. Thanks
@@Epictronics1 Oh OK I've just looked up the 8284's data sheet, and it already can output 2 different clocks, one for the CPU and one for peripherals. The CPU clock is divided by 3 from the crystal, and then the peripheral clock is divided in half again, from the CPU clock. So they probably are in sync. I dunno what the second 8284 does in the PC-SPRINT though, so can't be sure. Maybe they figured it all out back then, they knew more about ancient PCs than I do!
@@greenaum Both 8284 chips are used for 1/3 Speed on these boards. For your idea to work, the ISA bus must be somewhat overclockable. I'll test, thanks
@@Epictronics1 The ISA standard is 8MHz but I've read about people in the past who could run at 12MHz if their cards would tolerate it. Early overclockers! Whether that holds true for the Jr you'll find out!
So you mean the two 8284's are effectively in series for a 1/9 divisor? Why!? Or do you mean something else?
@@greenaum Not quite. The Sprint disconnects the CPU from the crystal and 8284A on the motherboard. It uses a separate crystal and 8284A for the CPU. This way we can overclock the CPU without affecting the speed of the rest of the system.
I love your videos, but please try to save as much hardware as you can. Just because it is cheap does not mean we have a long lasting supply. It just means it is in low demand. If these memory chips are no longer being produced, please try to save them. This goes for all retro hardware. We need to stretch this out as long as we can because the supply has an end.
Yes, this channel is all about preserving and doing fun projects with vintage computers and parts. However, when I have to, I always prioritize the motherboard because it's the rarest part
YOu should check out BBC's Building the great pyramid. It's an amazingly interesting film and it may answer some of Your questions assuming they are not answered by the guided tour. The series Egypt that accompanies it is also brilliant, especially the episodes concerning Tuthanchamuns tomb and Jean-Francoise Champollions work decoding the hieroglyphs. If you cant find them get back to me.
Great, I may have watched them already, years ago. I'll check, thanks!
Humans tend to do completely baffling things for three major reasons: addiction, sex, and religion. And while the pyramids aren't strictly speaking religious structures, they did serve as graves for the most powerful.
They're absolutely religious structures! They're all about getting the Pharaoh to his proper place in the afterlife, undergoing all the weird challenges dead Egyptians have to go through, before eventually taking his place as a god. That's what all the grave goods are for. The pyramids are as close to the Egyptian afterlife as they could build on Earth.