Your NPN / PNP transistor explanation was the best I’ve seen. Also am impressed by the schematic graphic with the indicator which shows what pin you are probing on the ICs. This makes your channel unique. Well done. You’ve got a new subscriber. PS: this is the first time I have ever commented on a KZfaq video so your work was that impressive. Cudos.

Your channel really deserves more subscribers. There are so many "retro" channels now but most of them are "I cleaned the keyboard in the dishwasher and retrobrighted the case" instead of actually knowing what they are doing.

Oh my god man, I just got a non working ZX Toastrack and couldn’t get a picture, a search got me to your channel. Thank you so much!! I have very little knowledge, but I found your video very novice friendly, I performed the same video chip test so I took a pint with what you said and ordered a TZX651. My soldering skills are fairly primitive but I now have a working toastrack!! Thanks again :)

Cool. I`ve got the same 1.4 voltage. I`ve already ordered the 2 transistors so this confirms there is a problem with them. Great help.

Fantastic repair session with 4 failing components! Thank you very much, since I learnt a lot from just this video!

So much destruction leads to one conclusion as to cause and you did mention it earlier in the video. Plugging something into the (totally unbuffered) expansion port while the machine is powered up is a huge no no and that is almost certainly what happened. I saw it so many times when repairing the 48K machines back in the day.

Great video again, Noel! Really enjoyed your methodology in diagnosing and fixing the issues.

Man, your videos are awesome. I just find it amazing how you teach everything with ease. Thank you!

Great stuff . Im doing a 128 plus at the moment. Will watch tonight . Thanks Noel.

I honestly thought you said nipple edition :-) wasn't sure what to expect. Keep up the good work.

Awesome repair job and well explained and logical process. After watching that, I've subscribed.

Hat off to you sir! This makes it understandable how to deal with large problems.

Another remarkable repair video from Noel (or is it Noël?). Your channel deserves far more subscribers.

famous last words "common fault" :)

Gran video Noel, estoy aprendiendo muchísimo sobre electronica retro, y técnicas de reparación, tengo un "Toastrack" y de momento funciona genial. Gracias por tus videos.

I was never into the Sinclair computers, so I know very little about them, but I find your videos and knowledge very engaging. Your need for sockets is very nice to see, even if you are using the inferior leaf spring sockets. And your meticulous clean-up of flux is also nice to see, so many old hack jobs left flux on everything.

Excellent video, Noel! Inspired to pick up troubleshooting on my own poor blown up toastrack again! And 16:08 : Too bad it's not a nipple edition indeed 😂😉

Awesome retro computing channel, Greetings from Poland! :)

Excellent videos and I want to add how much having those diagrams showing the pins being checked makes a difference. Thanks :-)

at 9:59 nice new transistors

Nice work and very fine explanation, greetings from Spain!

when I was in high school (back in Soviet times),i had to repair the spectrum 128. more precisely, it was a clone developed in the USSR. it was called "Pentagon" (because one of earlest the pcb have five corners ground field). this clone did not have ULA, and instead had many chips (counters, multiplexers, logic). the fault was caused by an incorrect power supply (Chinese 7805). first of all, all memory was burned out. memory-related multiplexers have burned out. the memory page Manager burned out... the highest bit of the address on the Z80 also burned out, but the processor remained alive. in the original zx128, the repair would have ended up replacing the ULA and Z80, but I had to spend a lot of time finding every faulty chip. I didn't have an oscilloscope, instead I used an old tube TV (as an indicator. connecting the video input to the inputs/outputs of the chips). there were no other options. .....didn't have any money for another computer. the repair was completed successfully. \ \ \ it was very interesting to watch the repair of the original zx.

Fantastic video, got a +2 that looks to be blown in a similar way. I'm not prepared to send it to silicon heaven just yet (not without a fight at least). Great diagnostic tips, much appreciated.

Great work. New fan. 👍

Nice video Noel.

Very nice video. Your explanations are very welcome :)

Great video ! Nice explination

I know you're saying nibble, but I kept hearing nipple. I'll go get my brain from the gutter....

nice job..thanks for sharing!

Looks like that transistor went out big style.

love your channel!

Well, that gave you the run-around. :)

Great Video

I would not have expected that you were taught "conventional" current flow. I learned electron flow back in 1974/75 when I went through training in the Navy. Either way is fine, as long as you understand what's going on and can apply sound troubleshooting principles (something you've very seldom had any problem with!)

Great channel great video! So was that ram chip faulty or was it all the BIOS chip?

Wow, how many breakdowns for just hot-plugging in peripheral. This action is something that we have gotten badly accustomed to with today's electronics, but disastrous in retro. Thanks for reminding us of the consequences ... although I probably forget it and I will connect the external DDI-1 floppy drive to my Amstrad CPC464 on without realizing it. :-)

Hi, found your videos a couple days ago and slowly getting through them, they are great! Just one quick question, which scope are you using for probing the busses and clocks?

Very instructive, takes me at a higher level to test defective boards. I liked the way to test the databus and the address bus. Now i have some reference. For the RAM chips, someone made a RAM tester and it works great. Did you find a replacement ULA or did you use the original one again. ULA is somewhat hard to find these days.

That exact CPU is still made new and NOS. Also might want to replace the power jack with a gold plated one just for better transmission. The composite mod would also make the display much cleaner and you can get small composite kit boards for around $10 USD.

Wow so many problems on one machine. Glad you got it figured out. please keep showing the oscilloscope and multimeter. It is great to actually see on-screen what we should be looking for. Have you ever been on bytedelight.com. They sell all kinds of spectrum mods. I just ordered one that uses the back port to connect with a rasberry pi to create an hdmi signal.

Great video as usual, thank you! It would be nice to see how those Data lines are supposed to read now that the ROM has been replaced? :)

I have a ZX Spectrum 48K that broke down because of the power supply went through a wrong switch cable and it reversed its polarity. It instantly destroyed the 7850, but after that being replaced it had very similarly symptoms: bad ROM, partially damaged ULA (working but after a while bad video signal) and bad Z80.

Hi Noel, nice video! With the final culprit being the ROM that seemed to corrupt the memory test of the RAM chips, did you happen to probe the data bus lines after the ROM change? I was curious whether the waveforms looked any different before and after. Do you think one or more of the ROM data pins was stuck high or low?

@Noel's Retro Lab : How are the data buses after the ROM replacement, are they more "straighten out" ? Asking cause i have some similar problem on a clone Z80, and i have the same suspect (ROM). I don't have the test cartridge to try it on(heck, i don't thing they are even compatible).

Wow!, that really was a mess :-( If it was a 48k speccy, all the ram chips would be hotter than hell lol :-D

How many people would have given up on such a repair? Your endurance in those difficult cases is great. I wonder how many Specrums would be in running condition today if you were the one who did the repairs.

I would look for a replacement for TR4. Something with similar gain but higher power dissipation.

I must echo other commenters that your transistor explanation is way better than text book explanations I have read (and reread, and reread, trying to understand) ... thank you! I had to relocate a scene in this video to be sure I was commenting on the right video. You were testing a transistor with your multimeter while the transistor was still on the board. I always wonder about how to interpret the results of an "on board" test like that. Won't other components on the trace always affect the result or are there definite rules about certain results regardless whether the component is still on the board or not?

Hi Noel. I have a Speccy +2 Grey with the same issue that the 128 Toastrack that you are repairing on your video. I know that essentially both are the computer, but I see all the components misplaced comparing with the board of the Toastrack. It lights the Power led and the cassette drive runs when a key is pressed, but nothing else... I wonder if the transistors you repaired are the same or not. Perhaps with different names too... Some idea?

Very didactic!

Repaired a c64 a year ago to play with it. I now want to get more retro Computers and try to repair them for fun. Btw I see you do a lot of desoldering, what gun do you use for desoldering? I’m thinking about getting one because desoldering with braid is pretty annoying, atleast for me😅

A Nibble😏 thats 4 bits as I learned last Wednesday.

Hola Noel, saludos desde Colombia, dónde consigues los chips de reemplazo para tus reparaciones?, Quiero iniciar mi negocio de reparación de computadores retro. Gracias por tus videos, son exelentes

@3:42 A question: You said, that you would measure pin 11(VCC) against ground. No I wonder, since the schematic shows only 8 pins on the right side (where pin 11 is), but the soldered TEA 2000 has 9 pins on each side and all seem to be soldered. How did you know, that you had to measure the penultimate pin against ground?

you should show databus signals after repair) also there is chineese component tester (TC-1) it can test a lot of components really fast (transistors also, and it shows actual punout of component, and other parameters (h21 and so on)) i think its`a good cheap solution. For high end - there are infrared cameras (seek thermal and others) that can show u which component is faulty even if its barely hot (29 deg celsius for example and others are 26)

At the beginning - current 666 mA, hell's power supply :)

my first computer was a Sinclair zx81, until i upgraded to spectrum 48k 😁

Hi! I replaced the membrane on my ZX Spectrum 128k+ "Toastrack" but it doesn't work, just the start screen. Can you please tell me what's wrong? Thank you

Hi Noel, I have a 128k "Toastrack" that's basically stuck on the menu screen. The keys register as I hear the beeps when pressed but I am unable to scroll down on the menu, nor will pressing enter do anything. Do you know what could be the problem? The system work fine before, only recently has it started acting up and I can't find anything about this issue online.

My spectrum 128 k still working my friend...

:_( I miss my old ZX Spectrum 128K

Noel, where do you get these awsome T-Shirts? (writing from Germany)

Something which I've always thought was n 'issue' when I've seen it on older boards is the 'warped' traces on the underside. Is this normal? I always thought it belied corrosion underneath the solder resist.

what the model number of your solder remover you used on the Z80? nice vid man.

one transistor fail took 4 chips dead amazing!!!

how interesting thing... the ROM, I would never figured it out.

If all this damage was done by connecting something to the user port, I wonder if it's possible to modify the board to protect it from such things? Maybe add diodes to avoid voltage coming in on the wrong pins?

Possible decoupling cap issues with those terrible rise times. i.e. low or no local voltage reserve. Pretty bad. I've seen some other scope traces where it was clear the decoupling was a problem in some other video's. One chip's signals shouldn't show up on the trace from another as a minor dip.

Oh cool, some Ferranti chips. I've got a rotary GPO phone that Ferranti made. Can't remember the exact year of the phone, but its probably a similar age to those chips

does anyone know what computer the 1084s monitor was most commonly sold with? I have a computer in a very old very worn and stuffed original box in a storage shed, and while I can remember the 1084s from the monitor I can't remember if the computer was a C64 or some sort of amiga(as its been many years since I looked at it and its a fair distance away, I remember it came with a bunch of expansion stuff(extra disk drive, ram expansion(that doesn't work anymore)) and the computer worked, but I had to bypass the power switch on the monitor, and the main OS floppy disk had a bad sector and I couldn't copy it due to formatting problems(basically I couldn't make a new disk with my PC floppy drive the format it uses isn't pc compatible) it used 3.5" floppies additionally, is such a computer worth hanging onto? while watching video's on old retro hardware repair is interesting, actually doing it myself/using it hasn't been for me for many years, and its taking up space, space I'll need to reclaim sometime in the next 6 months

cool video..i Just bought a toastrack off ebay..( untested) hope its not too broken :O)

Wow, how could so many parts fail at once?! Do you think maybe somehow static discharge or a power surge could have zapped it?

Why my zx spectrum with the composite video mod gives a good image in some lcd TVs, but gives very bad image quality in other lcd TVs?

I connected my ZX 81 to the wrong power output, it got 24 V. Not functioning anymore. Is it now completely toast? Can I try to save it ? (Or let someone save it bc I'm without electronic know how?)

Don't be silly, I'm not going to try and fix my computer: I'm going to send it to you :)

is the base always the middle pin out on a transistor ?

Hey Noel, Karl from the UK here. Just recently found you channel, and i Just wanted to say how awesome the videos you make are. Have you heard of a UK youtuber called Retro Man Cave? He's also quality, would be great if you guys could collab sometime. Keep up the great work, and thanks for the great content. :)

One of these days I'll try to fix my C64... :(

Something a little odd is that the ROM in both machines is an EPROM. Something to try would be erasing and reprogramming it.

I was taught electron flow not conventional flow like you use.

Is there a common cause to this many failures? I'm a bit confused.

I enjoyed the video, but for a ZX spectrum.. there's always the point where you have to think why continue? Make a new board with an FPGA.

Why don't you touch the top of the chips? More often than not the failed components get super hot very quickly, especially RAM. It could save you some troubleshooting time. I learned that from GadgetUK164's videos. Recently I purchased FLIR One Pro, it makes finding the failed components and shorts much quicker and easier.

It would be cool to have you as a neighbour :)

** ZTX651

Here goes the inefficient linear regulators again!

16:06 I can make out the text "RAM FAIL 012345678".