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@stewartclark3259
could be marginal drive current capability that the china chips failed for - someone got packaged rejects from the factory and remarked them, perhaps?
Комментарий от : @stewartclark3259


@AureliusR
Instead of using the signals directly, it's even better to use some logic chips to select the expansion RAM. Maybe an AND gate with CE and MEMW followed by an inverter? Something like that, I'd have to look at the schematic and think about it to get the logic correct. That way the 245 is only selected only when it both wants to read/write AND the correct addresses match. That way all those OE pulses wouldn't matter, they wouldn't get past the AND gate.
Комментарий от : @AureliusR


@scottgilson3247
The China chips are most likely SLOWER cheaper genuine parts that were remarked as faster. That would explain why one of the five China parts works - they're marginal. That they work in one PC vs. another can be explained by different bus loading, which can affect marginal parts. The fact that the 245 buffer helps is explained by it improving slew rate, which makes the timing better. A slower chip can pass with a strong fast buffer, since it only needs to drive the 345 and not the whole bus.
Комментарий от : @scottgilson3247


@jasonknight1085
Why not the option to map A0000-AFFFF? That was a common trick on T1000's and a few other machines as without UMB's you could just patch DOS to use a 704k limit... well, so long as you're not adding VGA.

Then you'd only have to map 64k into "true" upper memory.

Also isn't D0000 to EFFFF usually free, why did you start at C0000 in the first place?

Basically, needs more jumpers! :D

Комментарий от : @jasonknight1085


@johnathanstevens8436
I had an HX and I remember scratching my head at the PLUS boards at the time.
Комментарий от : @johnathanstevens8436


@fred_derf
For the 62 pin connector, I would have suggested going with two 30 pin connectors and sandwiching the 2 pin connector between them (rather than leaving handing on the end…)
Комментарий от : @fred_derf


@stevenbliss989
I would use 74F245 and NOT 74LS245 or WORSE 74HCT245, (slower and ½ drive ability of LS), ...the F family is much faster and 4x drive ability. If your SRAM timing is off some, any buffer (contrary to others advice) will make it worse! If it is a driving issue, then it might help. If you make a jump over plugs to bypass the 74LS245 and then use you CRO to see what the timing is doing, for comparison, ...otherwise you are working BLIND! Also watch your glitch generation in your decoding logic, it will cause trouble!
Комментарий от : @stevenbliss989


@CapnKetchup
My first PC was a Tandy 1000 EX. Great way to get into PC's. Especially with the Tandy DeskMate software to give it some functionality.
Комментарий от : @CapnKetchup


@alexabadi7458
Congratulations, very neat design !
Комментарий от : @alexabadi7458


@inlywang8157
Good job😃
Комментарий от : @inlywang8157


@new-knowledge8040
My first PCB, fully assembled, cost me a total of about four dollars. Anyhow, way back then, several of the cable TV channels failed, concerning horizontal locking, and so the screen picture was all twisted and scrambled. When looking at my TV control box RF demodulator output, you could see that the horizontal sync pulses were raised up to where they should not be, but only on these particular channels. This H-Sync pulse error appeared on every line, with the exception of those present throughout the V-Sync section. So I designed a little circuit that would pull each defective H-Sync pulse back down to where it is supposed to be. The working H-Sync pulses in the V-Sync section were left untouched, and each would tell the circuit when to look for the next bad H-Sync pulse. When detected and corrected, the corrected H-Sync pulse also was then being used to determine when to look for the next defective H-Sync pulse. And so over all it was fixing H-Sync pulse errors one by one, thus line by line. The circuit pulled about 10mA at 12 Vdc, so I simply put the assembled PCB inside my TV control box and used its 12 Vdc power supply. The circuit itself was then hooked up between the RF demodulator and the RF modulator. Bingo, all those pesky little channels with H-Sync problems now worked perfectly fine. The cable company called these specific defective channels, PAY TV channels, or something silly like that. LOL. Anyhow, for just a $4.00 fix, everything was working as it should be.
Комментарий от : @new-knowledge8040


@aleksandrbmelnikov
No pictures of Ralph Kramden?
Комментарий от : @aleksandrbmelnikov


@starsundsternchen802
What kind of engineer exactly you are? Seeing dozens of your videos, I was pretty sure, you are an electrical engineer. But then you have had made PCBs before for sure! I am confused. I actually don't know any electrical engineer that hasn't made a PCB in his professional life. But who knows!
Комментарий от : @starsundsternchen802


@eddieed_2328
get a IC socket with lever, to insert and remove ICs CONN IC DIP SOCKET 28POS
Комментарий от : @eddieed_2328


@Dorff_Meister
Awesome! I made my first two PCB this year (2021) and the both worked. I need to finish a revision and order a new one as my needs have predictably evolved.
Комментарий от : @Dorff_Meister


@steve6375
Did you check the voltage rail differences between the two systems?
Комментарий от : @steve6375


@rfmerrill
Whenever you have more than one board-to-board connector that need to be aligned with each other, sometimes you can cheat by just soldering while it's plugged in (just enough pins to keep it held in alignment).
Комментарий от : @rfmerrill


@jasondowns2778
Just got a stack of boards from PCBWay... time to start soldering.
Комментарий от : @jasondowns2778


@OzzFan1000
Curious: did you ever order updated PCBs and do they work better / without modification?
Комментарий от : @OzzFan1000


@francoisleveille409
What you call 'bypass' caps are really called decoupling caps. The spacing for your resistors is ok if you use 1/8 watt resistors.
Комментарий от : @francoisleveille409


@mk500
Love that RAM-access LED!
Комментарий от : @mk500


@BeatsUniversalOfficial
Nicee. We are a team of music producers - it would be great if you could take a peek at our instrumentals as well when you get a chance. Respect
Комментарий от : @BeatsUniversalOfficial


@arawndavies8525
"Something came in the mail today"
"What was it?"
"DEEZ CHIPS"

Комментарий от : @arawndavies8525


@MrWaalkman
Pretty much how all of my PCBs start out. :) Nice work!
Комментарий от : @MrWaalkman


@Calphool222
I think Adrian is my brother from another mother... I've been learning PCB development as well over the past year or two... I built a memory expansion card for the TRS-80 Model 1, and I literally did the exact same mistake on a bus transceiver chip (wired it backward). In my case I just crafted a little adapter that plugged into the socket so I didn't have to toss my PCBs.
Комментарий от : @Calphool222


@vjnobody
Pretty cool, but don't ever use samxon, capxon, etc. capacitors. There's a big list of good vs bad caps out there. The story goes that some bad designs were purposely leaked to make certain companies look like bad manufacturers. Many manufacturers used these capacitors because they were inexpensive, but they would self-destruct after only a few months or less.
Комментарий от : @vjnobody


@Elfnetdesigns
This was a really obscure place to find these but Toshiba made a similar module for the Strata PBX system (CRDU2A) as a daughter board for the main CPU board (MCBU4A or MDSU2) that houses a Z80-A CPU or the Toshiba clone (TMPZ84C00P-3) and a 64K RAM IC (TMM2564P). The daughter boards I have come into have only 8K of static RAM on them and a battery but I assume those can be upgraded to larger capacity IC's. The Boards as a whole can still be found online but at collectors rates however many businesses seem to be ditching their old PBX systems for IP phone systems so with some looking you might be able to come across a whole system for cheap or even free via trash bin fishing.
Комментарий от : @Elfnetdesigns


@albertynung1628
OMG premiumtoolsaid,com are awesome, I received $8000 from via hack service
Комментарий от : @albertynung1628


@michaelblair5566
I am thinking of building an 8088 XT type PC to play old DOS games. Maybe get an old Tandy 1000....
Комментарий от : @michaelblair5566


@blackcathardware6238
Good work. I made more mistakes on my first PCB for the Atari ST.
Комментарий от : @blackcathardware6238


@PCBoardRepair
At 7:07 you have a 74LS240 and It should be 74LS245
Комментарий от : @PCBoardRepair


@JeanMachado
perhaps, as the Chinese chips are re-marked, it is possible that they are slower than indicated, perhaps 70ns. I saw some old data sheets that show this access time, and associated with hct-based chips, capacitors and a good PCB, improved the access time enough for the good functioning of the Chinese chips.
Комментарий от : @JeanMachado


@JNET_Reloaded
why cant you put like a gb ram in it?
Комментарий от : @JNET_Reloaded


@omarhammoud7223
Adrian what brand is that soldering iron?
Комментарий от : @omarhammoud7223


@lapulla32
Hi, I just start to watch your videos and bring me flashback when I got my first PC, Tandy 8086 1987. Also the Assembly language from my PC class in University. Looking your situation with the Chinese chips, Did you try to check the voltage with the Osci or a meter. Sometime they fabric this chips with less silicon in the transistors. And then they check them using a standalone tester with enough power.
Комментарий от : @lapulla32


@AmadeuszKlodawski
An amazing ride, from the initial troubleshooting to the discovery of the fake chips, to a finalised board. Truly a fascinating series of videos.
Thank you for your hard work, both on the video and the board design; and, of course, for sharing the finished creation.

Комментарий от : @AmadeuszKlodawski


@flamespear86
Why does he hate RF shields so much?
Комментарий от : @flamespear86


@cheath8705
Tandy 1000HX was my very first computer in my life for a year or two before I moved on to a 386sx 25mhz machine. Just surprised to see you actually worked on the memory e pansion. I recall that 384k expansion card cost $600 and the 386 was costing $200 with 1 meg ram. I badly want to upgrade the Tandy because it was a nice machine but upgrades was just not worth the price.
Комментарий от : @cheath8705


@antonnym214
Not bad for a first effort! I admire your troubleshooting skills. All good wishes!
Комментарий от : @antonnym214


@PsyckoSama
Might want to change the distance of that one capacitor, first chip top row. Looks like it'll interfere with a chip puller.
Комментарий от : @PsyckoSama


@flyguille
As always my theory was correct.
Комментарий от : @flyguille


@jessen600
How much would it cost for you to make one for a view? Factor in costs of materials, shipping, and a reasonable amount for hourly rate for yourself.
Комментарий от : @jessen600


@garydunken7934
New comer here. I really love these videos.
25:12 showing the mistake/errors and then showing the learning is quite motivating.

Комментарий от : @garydunken7934


@TechnicolorMammoth
Your music choice, sir, is indeed choice.
Комментарий от : @TechnicolorMammoth


@gaming53wishmaster71
now to figer out how to use this type of tech but on pci exprass lmao
Комментарий от : @gaming53wishmaster71


@themetalmicky
can i have half your brain please
Комментарий от : @themetalmicky


@elouisevanhelsing3430
Let us know if you solve the HX problems... I am really curious!
Комментарий от : @elouisevanhelsing3430


@Calphool222
When I've built memory expansions for other old computers (TRS-80 Model 1, Apple IIGS), I've sometimes had to merge the address decoder with the CE/OE lines for the bus transceiver... otherwise I would get into weird situations where my ram was being activated when I didn't expect it to... sort of like what you had happening here. It all sort of depends on the details of the timing, and it's really easy to confuse yourself with the timing diagrams. Super easy to get something "close" to working, but not "quite" working... and then you're scratching your head for a while. ;-)
Комментарий от : @Calphool222


@samuellourenco1050
Apart the mistake, the board is actually well designed!
Комментарий от : @samuellourenco1050


@VoxelPrismatic
why did you put rick back there 16:58
Комментарий от : @VoxelPrismatic


@saddle1940
Just 2c worth.

AND the memr and memw together and OR the output to your CE line to get the OE\ for the 245. Wire the MEMW to the dir. Use a single NAND chip to do the job. 74LS00.
Wire the CE to both inputs of gate A to invert it. Wire MEMW and MEMR to the inputs of gate B. Wire the outputs of gate A and gate B to inputs of gate C and wire the output of gate C to the 245 oe\. One chip and you can reuse those boards you made.

Комментарий от : @saddle1940


@inferior2884
JLCPCB
Комментарий от : @inferior2884


@PimpinBassie2
Don't use sockets for everything. I have an non-working Atari TT030 which has sockets all over the place.
Комментарий от : @PimpinBassie2


@richardkelsch3640
Instead of one large connector and a bodged tiny one, why not just use two half-size connectors? The strength would have been better.
Комментарий от : @richardkelsch3640


@chonghome1511
The level of geekiness on this channel is amazing and it just fits my bill. I know enough to just follow along and you almost lost me on the Oscilloscope traces, but it was worth sticking through till the end.
Комментарий от : @chonghome1511


@Sharklops
This video has given me enough confidence to just give it a go and try and make something simple. Any thoughts on the best free layout tool for a beginner to play around with?
Комментарий от : @Sharklops


@AndyDavis007
while I don't have a Tandy to make an expansion board for, I really do appreciate all this work and this video. Thanks again for your work.
Комментарий от : @AndyDavis007


@RodBeauvex
Is it just me or does a tiny moth fly out of the case aty 12:25?
Комментарий от : @RodBeauvex


@michaelblair5566
Interesting. I've been into PC's since my first 80286 back ib 1990. I've been a systems and networks guy since 1995.
Комментарий от : @michaelblair5566


@nunyabusiness7602
One of the most interesting and informative videos I've watched on YouTube in a while. What's the likelihood of adding a DMA chip like the original 640K PLUS expansion board had? Do you plan to make these available for sale at some point, either assembled, kit form, or just the PCB?
Комментарий от : @nunyabusiness7602


@CitroenGames
i dont see a problem with buying parts from aliexpress
Комментарий от : @CitroenGames


@shamrice
Nice vid!

Btw, is that a Rick Roll at 17:00 in the background?

Комментарий от : @shamrice


@tactileslut
The guy who wrote your logic analyzer's print routine must have owned stock in someone who sells ink. White on black is cruel.
Комментарий от : @tactileslut


@onjofilms
I once ordered a PIC32MX evaluation board from Microchip when they came out, and guess what? No bypass caps were installed. It worked fine.
Комментарий от : @onjofilms


@simant5361
really enjoyed this
Комментарий от : @simant5361


@dan2800
maybe the prototype doenst work bc latency and sram from china is good
Комментарий от : @dan2800


@75slaine
Really cool series Adrian. Thoroughly enjoyed it. Nice debugging of the board issues 👍
Комментарий от : @75slaine


@davehohacks
The first board revision always requires at least one bodge.
Комментарий от : @davehohacks


@NewsmakersTech
That's amazing! We may have to build a few..
Комментарий от : @NewsmakersTech


@GeorgeGordonNCA
Use some stitching Vias to connect the ground planes on the top and the bottom. It improves signal integrity and reduces electro magnetic emissions / interference (EMI).
Both helps getting stuff more stable at high speeds. High speeds: Bascially everything in a computer as there are square waves on all the lines. :)
Easiest way: Enable "remove dead copper" (or whatever that option is called in KiCAD - Have to learn that program some time :D ) and then just put vias in until there are no holes left in the copper-fills. After that put vias next to all the signal-lines to ensure every trace has the shortest possible ground return path. Takes a bit of time, but the reward is higher possible speed and less hard to find problems caused by signal integrity that can only be found by using ultra low capacitance active probes on high end Oscilloscopes. I personally ran into signal integrity problems on a 400kHz i2c-Bus with a 2-Layer board when I was doing my bachelor project. :)

Комментарий от : @GeorgeGordonNCA


@greggv8
How about a LIM EMS board for the EX and HX? Bump that up to 2 or 3 megabytes.
Комментарий от : @greggv8


@greggv8
On EX vs HX, have you checked the RAM timing requirements for differences? If the HX has tighter timing where it expects RAM to be ready for reading and writing sooner then the iffy Chinese chips could be just a bit too slow, with the one that works all the time on the EX being just fast enough but too slow for the HX.

What I did back in the days of DIP RAM and 72 and 30 pin SIMMs was install RAM faster than specified. That would speed up the computer because the RAM would be ready right at the start of each read or write cycle rather than somewhere between the start and end of the cycle. The speed difference was easy to see during the RAM count up during POST. With an audible tick the difference could be between being able to distinguish the individual ticks and a quick burst of noise. For those the specified RAM speed must have been at or near the end of the cycles, with the system sitting around wasting many nanoseconds on each cycle.

When DIMMs came along, systems that used them had much tighter, shorter, RAM cycles so speed differences became something only a benchmark could show, or perhaps a bit of time difference over the course of a long process like generating a fractal image or converting WAV files to MP3. Still a significant difference if you were doing things the PC had to crunch numbers on for minutes or hours.

Комментарий от : @greggv8


@jeffscyclingchannel8154
Fascinating! Still need more tools.
Комментарий от : @jeffscyclingchannel8154


@JeffGolenia
I recently made my first board also. It's a cpu and ram board for the Motorola 6800 series processor. Took me a week to track down the one flaw - I didn't realize the EPROM's Vpp pin needed to be tied to Vcc. Now it's running the MIKBUG firmware and BASIC. It's meant to be part of a backplane system like the rc2014 Z80 project. I'm currently working on rev2 of the cpu board, an i/o board, and a debugging board with til311 displays, a serial debug output and the MIKBUG rom. The first board was the hardest, now its full steam ahead.
Комментарий от : @JeffGolenia


@electronicsluckydip
Apologies if you have discussed this in a previous video but I was wondering if you're not grounding your TS-100 sodlering iron. Or perhaps you have it powered by battery. No need to reply - Just making sure you have that covered!
Комментарий от : @electronicsluckydip


@yukisaitou5004
You should swap the LED for an RGB one on the next revision since RGB RAM is all the rage nowadays ;)
Комментарий от : @yukisaitou5004


@emorelama
Hi Adrian.

I have also recently started designing PCBs. I started with Fritzing buy I would like to switch to KiCAD too. Can I ask you what tutorial, book, documentation, ... whatever have you followed to learn? Despite the mistakes, your PCB have a great looking.
I see all your videos. Thanks for your work...

Комментарий от : @emorelama


@awesomefacepalm
I'm doing a course in electronics design at uni right now and we're covering PCB design right now, it's super interesting, and fun to see your board design and see how you did it with KiCAD.
We're not using KiCAD though, but rather an 8000$ professional design software 😮

Комментарий от : @awesomefacepalm


@kelli217
Cool project! I wonder if anyone is doing something like this for storage... something like an XT-IDE.
Комментарий от : @kelli217


@jengelenm
Amaaazing video! Where do you get all that knowledge, are you a high-level, university scholed electronics/IT engineer?
Комментарий от : @jengelenm


@TomStorey96
If at first you don't succeed, call it version 1. Oh wait, you already did. 😄
Комментарий от : @TomStorey96


@keiffitz689
As an electrical engineering student, I can’t help but marvel at the time and effort you put into these projects. Nice work, and keep it up!
Комментарий от : @keiffitz689


@rich1051414
Maybe a schmitt trigger for the data lines would help with the HX compatibility. Not sure it is worth it at that point though.
Комментарий от : @rich1051414


@rich1051414
Right from the Vic-go?
Комментарий от : @rich1051414


@helldog3105
Cool! Now all I need is someone to help me clean up the Tandy 1000 HX that I have that had sat in a flooded basement. I want to restore it, but I need to learn how to remove the rust from the PCB without damaging it, as well as rebuilding the PSU for it, because I'm certain that got rusted as well. Surprisingly, the keyboard and floppy drive were not effected, nor was the serial card or the tandy memory card that was in the system. But the bottom is stained really red and even though I have tried cleaning it with soap and water, I can't get the discoloring removed.
Комментарий от : @helldog3105


@scharkalvin
The bus transceiver won't correct for slow access time, in fact, it will make that problem worse. However it will correct for low drive (fan out).
Комментарий от : @scharkalvin


@FurrySergal
My Tandy EX has been sitting for a year now because of the RAM limitation and resulting incompatibility with a lot of the software I want to run.. I should get back into that thing.
Комментарий от : @FurrySergal


@hollgo626
Congrats for your first step in hardware development, thats really the master discipline in the world of hobbyists computing .
Комментарий от : @hollgo626


@colonelbarker
I'm glad the 245 helped! Looking forward to seeing the upgraded board.
Комментарий от : @colonelbarker


@stephenbell9257
Before redoing the PCB design you should check that the timing of all signals is OK using an oscilloscope, not a logic analyzer. An oscilloscope can show subtle timing variations and signal quality issues that a logic analyzer will ignore.


The fact that you are getting some of the fake chips working in some combinations of units suggests that the timings might be marginal. It might be that the fake chips are slower than marked but you need to verify that all signals comply with the timing requirements (preferably with some extra margin) for the CPU on the motherboard for reliable operation.

Комментарий от : @stephenbell9257


@charlesparmele
Interesting.
Комментарий от : @charlesparmele


@SidneyCritic
They make FM headers with extra long pins so they are a pass-through with FM on one side of the PCB and M on the other, you just have to side the plastic strip from a M header over the soldered joints.
Комментарий от : @SidneyCritic


@danweecc
Another possibility is that the ability of the RAM to drive the logic in the respective PC circuitry is different. The bus transceiver becomes a buffer that enables the drive capability. Different chips have different fan out. You may want to scope the data bus to look at the quality of the signals between the two computers. It is possible that the "good" chips have better drivers.
Комментарий от : @danweecc


@Nono-hk3is
The number of times I've modified a circuit and sent it off for printing without breadboarding the change....
Комментарий от : @Nono-hk3is


@beatadalhagen
Congrats on making (and debugging) your first board! Mine own very first (not including hand etched) board makes a decent bookmark and the second is useful for aligning 3D printers.
Комментарий от : @beatadalhagen


@CenterpointConnect
When I had my HX, I always hoped of one day getting 640k....
Комментарий от : @CenterpointConnect


@brandontechnerd
I think this channel is worth it just for the VHS intro.
Комментарий от : @brandontechnerd


@jimgrady7458
Ok, any video that mentions DigiKey in the first 30 seconds gets an immediate "Like" :)
Комментарий от : @jimgrady7458


@SamuliTuomola_stt
29:05 might be combination of couple of things.. at 7.16MHz CPU is expecting data from SRAM in <400ns + the 8088 clock generator has a feature to inject wait state cycles 8051-microcontrollers.blogspot.com/2015/08/80868088-hardware-specificationsready.html#.XcDjqZMzZo4 in order to deal with slow EPROM .. I'm guessing the china SRAM is relabeled slower >400ns chip and the wait state logic happens to work a bit differently in the other computer. should be possible to verify with a logic analyzer.
Комментарий от : @SamuliTuomola_stt


@jaybrooks1098
Timing error? Without the fancy chip?
Комментарий от : @jaybrooks1098



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