Tandy CM-1: A broken high-end 26khz monitor from 1984

[@yakmage8085]

No groan over here. I love the crt videos

[@jamiecruickshank9697]

Same! I seen another CRT and was excited to watch 😀

[@barnyardproductions1649]

Same here I'm always excited to see a new crt video

[@aaron5364]

Same.

[@NeoNyder]

Me too, especially RGB monitors from that era.

[@bengelman2600]

Same here

[@runderwo]

Another museum quality device saved from the dump all thanks to newer technology and determined people like Adrian.

[@jeromethiel4323]

When i was working at Computerland in the mid 80's, we sold some stupidly expensive monitors. They were intended for CAD use, and required a full length graphics card to run. They had 4 BNC connectors, one for each RGB color, and a synch cable. 19" CRT monitors with a crazy high (for the time) dot pitch. Only sold a few, as the monitor alone was more than the computer you put it in. And don't get me started on the video card, it was almost as much as the monitor. And that wasn't the worst part. You then needed an extremely high end plotter to get anything useful out of the system if you wanted hard copy. All this for a very early version of autocad, running on an IBM PC. Slow was the operative term here. But it sure looked pretty!

[@burnrubber7547]

Just goes to show every single component, no matter how small, is important to the operation of the system. Really enjoyed this. Good work Adrian.

[@rasz]

Earl William "Madman" Muntz disagrees.

[@keithkneeland6849]

@@raszTrue, but he never made a computer monitor 😉

[@agranero6]

I was screaming at the screen since you determined it was not the CRT : it is the capacitor! Notice the "smearing" wave looks more like a cap charging slowly than a linear one. I thought the capacitor had a leakage, but you proved it wrong. It was not the butler, it was the maid! Very nice monitor and very nice video.

[@ytmadpoo]

Yeah, those RC circuits are generally to help improve the ramp rates during voltage changes. It's a fascinating subject of its own, and during my EE days in college we spent a hefty chunk of time on those. They can be simple like that or get quite complicated (like, you want your Q time to improve, but don't want ringing either, or keeping the ring to an acceptable level). Don't feel bad that it takes a while to grasp, and I've probably forgotten all of the details myself now that I think back on it however many decades later. You grasp the fundamentals though about measuring what voltages should be and eventually getting to the root of the problem and that's awesome. Keep at it! I enjoy vicariously going through the troubleshooting process. :)

[@burn0u71]

Adrian, your inexperience is worlds better than some people's extensive experience. just sayin. keep it up. your videos are freaking awesome and very informative.

[@ingwarnilsson668]

His patience is the Key.

[@kennethflorek8532]

Adrian has professional fearlessness. You have to have that to learn to fix nostalgic, obsoleted things. Whatever experience that once existed has also been obsoleted. What did Adrian do before that strengthened this virtue?

[@chuckbenedict7235]

I don't mind seeing a CRT getting fixed. What I love about your content is the desire to step-by-step logic your way through a problem. And you explain your thought process well. Once I saw the scope trace, I thought there must be a bad cap somewhere. In this case that intuition might have led me to the solution quicker, but breaking from a very methodical approach also can lead to frustrating dead ends. Nicely done!

[@GrangerMeador]

Wow, this brings back memories. I bought a Tandy 2000 with a CM-1 monitor back in 1985 for $2,750 when I was a student at the University of Oklahoma. I loved its high-res display, although it never was as bright as the yucky monitors at work. I was grateful that WordPerfect worked on the machine, and I remember buying the Tandy 2000 versions of Microsoft Flight Simulator, Lotus Symphony, and GEM. Good times!

[@Merescat]

Boomer!

[@klaatubob]

The Tandy 2000 is the only PC i ever knew of that used the 80186. The machine bombed so badly that Tandy ended up using them in the backroom of every radio shack store with a monochrome monitor. It had the store operating system on it and the employees had to manually type in every paper sales slip at the close of the day and then transmit the daily report to the head office in Texas via dial up modem. They ran MS-DOS 2.11.

[@piero_75]

If someone had told me 20 years ago that I could watch a video of a guy fixing a CRT monitor whilst I had my breakfast I would have truly thought the future is on its way!! Fascinating to go on the repair journey with you.

[@jonathanwhiteside6092]

That monitor looks to be in excellent overall condition, it's lovely.

[@DerIchBinDa]

I am relative new to electronics repair and analog stuff like CRT is still above my skill grade, but that was an fantastic look into how it works and a great ride along the way to the solution. You really are gifted and entertaining while doing your repairs, chapeau!

[@jwhite5008]

Absolutely true. I also know very little about the analog stuff and next to nothing about CRTs but Adrian is so pleasing to hear talking and he explains stuff so well! No other channel I know of does that to this level.

[@mistermac56]

The cheapest passive components can be a nightmare, as you discovered. You learned a valuable lesson in diagnosing analog circuitry. One of my EE professors always told us to check passive components first. He came from the old school of vacuum tube tech. He taught a elective course in vacuum tube theory and I am glad I took that course.

[@theturtle32]

Despite the naming, the 2000 actually came BEFORE the 1000. It was not intended as a higher end version of the 1000. Rather, they learned a from a lot of their mistakes with the 2000 - particularly around IBM PC compatibility - as they designed the 1000.

[@RadRat78]

No groans here, dude. I collect the old monitors and truly enjoy these episodes.

[@R_Squared933]

If it's any consolation, your "fumbles" are what helps me think more critically in what I do. Different paths, that I probably would have bypassed, or not even thought of. Thank you.

[@FinalBaton]

Your crt content is some of my favourite! I'm a crt maniac, it's probably my fave part of retro gaming and computing.

[@pb_magnet]

6:18 anyone else go looking for their Discord notification? 😊

[@samueltoogood5703]

Yep

[@v4lgrind]

Sure did

[@jamiecruickshank9697]

Haha, I skipped the video a few times to check 😂

[@adriansdigitalbasement]

ROTFL -- sorry I usually keep my Discord tab muted, to prevent that exact thing!

[@Synthematix]

Whats discord?

[@chrismansi4855]

What a great video! I sincerely hope I never actually need to troubleshoot and repair a monitor like this, but if I ever do, this video does such a great job of showing how to think logically about where the issue may reside, and troubleshooting steps someone could take. Thanks as always for your work!

[@jkweb3]

I’m so proud of myself that I immediately suspected and was screaming at the screen that it was a pull down resistor problem. I’ve learned so much more from your videos then I even knew :D

[@dawnmitchell8213]

One can only watch so many videos related to retro computer repair before they all start to repeat so mixing up with stuff like this keeps the channel fresh and teaches people troubleshooting skills.

[@DavidBrant]

Love your CRT videos! No groan except when the video ended! Thank u for saving another CRT life. ❤

[@RobotnikPlays]

Yeah gotta say I find the old CRT videos the most interesting. Well, generally any sort of troubleshooting, but each CRT is kinda unique and quirky, and not as well documented as say, the C64, so it's always interesting watching someone open one up and just prod around finding things.

[@marcseclecticstuff9497]

I started working on TV's in the late 70's. I've always cleaned & applied silicone grease around the HV Anode caps just as a matter of course. If I can do a bit extra for little money/time I do it to show my customer/employer I care about doing quality work. In reality, I think the only time it would really matter would be in very humid environments especially if a lot of dirt/dust has accumulated in the area that can trap and hold the moisture. Otherwise, I'd agree that it's really not necessary assuming the rubber is still in good condition.

[@greenmoose_]

That "eureka" moment when you found the bad resistor! Love these videos!

[@LoranFrank-b4u]

Adrian I truly appreciate the post especially with a Tandy CRT you saved a vintage Radio Shack so it can be enjoyed again.

[@Ojref1]

Silicone grease is a secondary dielectric measure for that cup. It prevents arcing in case the yoke gets dusted with conductive dust. I.e. the monitor sitting out in a manufacturing plant floor where the air might have graphite or fine metal dust. Probably helped them meet/exceed ratings in different markets when it was being manufactured.

[@tomothywalker]

Really appreciate this man. I used to steer well clear of CRTs, but your videos have given me the confidence to get in there and diagnose, and I’ve fixed a few now. This one is next level awesome!

[@mckinnon42]

Hi Adrian, I wanted to comment to let you know I adore you're positive attitude. You mention complaints about 'another CRT video'. I know you have to be conscientious of popularity and the algorithm as this is your income, but I strongly urge you to look more to your data and analytics and less to grousers. The focus on negativity can be heavily corrosive and eat away at your enjoyment of the process. Anyway, that's enough from me. Thank you very much for sharing your passion!

[@nigelrhodes4330]

I own a CM-1 in Australia, I knew nothing about it till this video, thank you now I know that it is of little use to me I will probably get it to a place that can use it.

[@Agnemons]

The CM-1 and to a lesser extent the VM-1 are quite hard to come by. Quite often the TRS80 2000 will be listed for sale but with no monitor which makes the computer, at best. a static disply item. Being from Australia it will a 230 volt 50hz unit some even rarer. If you are interested in it finding a good home, hopefully attached to a working 2000 I can give you some contacts in Australia that may be able to assist.

[@cgbolton1]

Hi Adrian, seeing this monitor brings back tons of memories. I worked for Radio Shack in Ontario, NY back in the late 1980s and before we had POS systems to input our sales, we wrote receipts by hand and then at the end of the day we had to enter all the tickets into the trusty Tandy 2000 in the back room. That T2000 had CM-1 monitor on it. When the store retired that computer I managed to buy it but alas its lack of PC compatibility made it really nothing better than a brick to my younger self. Eventually I got a Tandy 1000 TL/2 but even that computer is long gone. I have managed to get a 1000EX that I’m working to restore but finding a CM-5 or CM-11 is getting harder. Maybe someone watching has a spare that they would consider parting with.

[@johnglielmi6428]

I did notice that on the bottom the the main board there was an electrolytic cap that went missing after you removed the glue. Maybe that was a filter cap, and it is causing your bleeding issue. Hard to tell without knowing how the schematic looks for that part of the circuit. Otherwise great video as always. you're a great teacher, and go to great lengths to get the layperson to understand.

[@met9009]

I have been watching you channel for years. I had one of those Tandy 2000s. I couldn't find really any software back when I was a kid. I would just do basic programs. I remember being so disappointed with the graphics when I upgraded computers with a cga.

[@thirstyCactus]

Nice find! I've been missing the catharsis of watching you fire those dead components into the bad parts bin!

[@gizmosx84]

Thanks, Adrian, for this awesome troubleshooting and repair. When you learn something new, we also learn from you, keep the great work ,wishing you all the best

[@750kv8]

This was a very elusive fault, great job fixing it, Adrian! 👍👌

[@maniatore2006]

I love your Monitor and even TV Videos, thank you so much for that Video.

[@nikelquint]

Wonderful diagnostic work Adrian

[@joshhiner729]

Love the crt videos. This was a great troubleshooting demo. Ive learned so much from this video and of course all past videos. Awesome

[@insanemal]

In the end of the video, where you did the long piece to camera the focus was hunting quite a bit. I usually use locked focus for those bits with as large as possible F stop for the biggest depth of field possible. But really locked focus is really going to be a must for those shots. But thanks for an awesome video and keep up the awesome work man. Seriously love your content!

[@AK-vx4dy]

20 year later...next guy..."I must definitely remove this horrible hot glue"🤣

[@CRSolarice]

In all of the years that I have watched videos from ADB I haven't seen one that I didn't like (but I believe that its a good idea for the author to always have that question in mind because if you don't then all of your videos are great and you won't be capable of improving or even realizing the necessity for improvement. Its like if you know everything then there is no 'space' for you to learn anything new. Modesty is one of the best routes to improvement).

[@KennethSorling]

Never apologize for making monitor videos. I love monitors! In fact, I think I have a slightly unhealthy obsession with the god forsaken things. Videos about obsolete CRT tech is my kryptonite.

[@user-rs8zg8ey2b]

I worked on that thing when I worked for Mitsubishi from 84 to 90. Mitsubishi was a great company. I worked my way from 8", 5.25", c/e/vga, controller cards, video, storage (mfm/rll/SCSI), then motherboards.

[@alisharifian535]

If I can learn something and have fun, I will watch. No matter if it is about a monitor.

[@PhuketMyMac]

I love monitor repair videos. Love CRT repairs. Please keep them coming.

[@hapskie]

Well found sir! Really unusual for a resistor to fail, never seen that before.

[@jwhite5008]

That would be the LAST component I would have checked. How the heck did it manage to fail (and not charred)?

[@Renville80]

Carbon composition resistors (the cylindrical brown ones) in older radios and TVs have a very strong tendency to drift out of tolerance as they age. The more modern metal-film ones can fail if stressed, but can 'hide in plain sight' when they fail.

[@fumthings]

@@jwhite5008 how indeed. if i understand the scope traces at 39.43 the cathode is reaching zero volts some of the time. so is the resistor punching through and being 100 ohms again then rising to high resistance some time later? totally weird why didn't it just stay open? 90 volts in the circuit?

[@deplinenoise]

Great work on this one! Always love the detective stories.

[@paincreatesfame]

I love the monitor videos! I may not have grown up when these CRTs were new but I still have fond memories of CRTs in my home as a kid (early 2000’s lower income household, if you know you know) so I always enjoy seeing one of these bulky bois in a video.

[@mrflamewars]

Growing up my family had a Tandy 1000 with a CM-5 monitor and the dot pitch was best described as "you can drive a bus through there"

[@brentboswell1294]

The Tandy 2000 was Tandy/RadioShack's original MS-DOS machine. It could run MS-DOS applications that used proper systems calls, but not IBM PC applications that used CGA graphics. (MS-DOS architecture didn't originally include graphics, as it was more like CP/M). It also had a nonstandard disk format which was incompatible with the IBM PC, but stored much more data on its floppies. The Tandy 1000 was next, and was kind of a "Mea culpa" move by Tandy, as Compaq demonstrated for them the importance of full PC compatibility. Whereas the Tandy 2000 was only advertised as a business machine, the Tandy 1000 was advertised as a high end home and hobbyist system.

[@adverschueren]

Hi Adrian, with that faulty 100 Ohm resistor, the drive signal could still be pulled down to ground, but that was done by the first transistor via coil L651, diode D692, resistor R667 and the base-emitter junction of the PNP transistor (acting as a diode). This must have overloaded the first transistor, leading to the smearing.

[@twocvbloke]

Nah, more CRT videos are welcome, it's nice to see them come back to life, especially when it highlights how the brown goo is killing electronics if left in place, also is pretty fun knowing that this is the monitor that VWestlife pointed out too, wonder how many enquiries the seller had about it back when his vid went live... :D

[@alfonsotoledo8009]

man, i've been anxiously waiting for a crt video!

[@briangoldberg4439]

absolutely love the monitor videos. they are my passion; i repair monitors here at home all the time

[@quakesin1982]

I love your CRT repair and troubleshooting videos!

[@The1RandomFool]

I thought this would be the repair of the computer from the mail call episode, but hey, I'll watch this too.

[@tcrime]

I always your enjoy your CRT videos, personally. As for the faulty component, I recently fixed an NAD receiver that was entirely prevented from working by one bad resistor keeping everything locked in a protection mode. That bad resistor showed no outward signs of damage either, so perhaps it's more common than we think.

[@shanemshort]

as soon as I saw that gradual ripple I said out loud "ooh, that's a bad pulldown surely" and I'm so chuffed I guessed correctly.. seems like watching all these videos is starting to pay off xD

[@nicktasios1862]

That’s so awesome about RGB monitors; the circuits for each channel are duplicated so it’s easy to compare voltages or use diode mode to troubleshoot. I used the latter method to find a faulty RGB amp on a Sony monitor.

[@trance_trousers]

55:14 You gave me kittens thinking you were going to short out some of those joints with your probes! Enjoyed the video though, and great fix!

[@GiammarcoZacheo]

You are a true artist of troubleshooting.

[@maillouski]

Analog stuff is weird but very interesting. It’s mind bending and very interesting to me for that reason!

[@thirstyCactus]

Pro tip: if you sling the AC cord over your left shoulder before lifting the back cover, you can then more easily pull the cord through from beneath, using left hand, whilst holding the cover with the other hand.

[@imqqmi]

Had an open resistor once on a hp IPS monitor PSU, same thing, no visual damage. Those faults are challenging to find! Job well done! The signal looked like an oscillation to me, with some damping. Could be one or two transistors started oscillating with the open pull down resistor.

[@bishopofrustyiron3101]

No groan here just a cheer!! Nostalgic throw back to Radio Shack, where I grew up as a kiddo in front of old black and white CRTs learning programming, there in the store.

[@galeng73]

I just noticed the TRS 80 sticker on the monitor. I chuckled. Also, I'm not too picky. I don't mind monitor content.

[@duanerobinson935]

The manual makes me miss the days of technical writers for documentation creation.

[@jrnovosel]

I had that monitor and card back in the day with my Tandy 1200. If I remember right, the monitors were heavily discounted by that time (no way I would or could have paid full price). I think even the 1200 was discounted by the time I got the whole bundle (no hard drive) from RS in around 1986-1987 It was a great monitor though and I had a couple of applications that used full resolution (VersaCAD I think).

[@adriansdigitalbasement]

I can believe it, as these monitors were expensive when new, but quickly became boat anchors no one really wanted. So it makes sense you might pick one up on a big sale and pair it with the STB Card on a non Tandy-2000 for some nice 400 line action.

[@tomstdenis]

problem solving videos are always cool even if I'll never open a CRT myself :-) (I don't even own one anymore). keep on!

[@tekvax01]

Nice job Adrian, I would have jumped to conclusions and thrown the CRT regen on the red tube, and likely made it worse...

[@oledave2540]

The monitor and disk drive videos are my favorites.

[@KING_VHS]

Watching this and seeing the text appear with a glow was very pretty to me.

[@thirstyCactus]

Fascinating! I've only seen the 80186 used in embedded systems until now.

[@mikebarushok5361]

There were some 186s used on adapter cards for the PC, but the Tandy 2000 came closest to a successful system using it as the main processor. I remember a full page color ad with a young Bill Gates talking about the Tandy 2000 being the next big thing.

[@SilentShadow-ss5xp]

I think for longevity and reliability the grease should be applied. It still help keep the connection sealed from the environment and help to keep dust and moisture out. Plus if it happens to be in a garage or something and gets wet while in storage the water is less likely to get inside that part and destroy the tube.

[@erickvond6825]

What you're most likely experiencing here is a marginally functioning transistor. It tests good but while it's in circuit, it's faltering. I'd try putting a new part in where you found the discrepancy in the signal. At least that's what I thought until you found that open resistor...

[@frankowalker4662]

Great work Adrian.

[@adelestevens]

Great video , I actually managed to understand what you were talking about. I must be getting this CRT thing now.🤣

[@Brian-L]

Nice sleuthing! Every small oversight becomes a lesson learned and another tool in your toolbox.

[@simontay4851]

Those tiny 1/8 watt resistors are nasty little buggers. I had to replace one in a switch mode PSU. It was the startup resistor for the UC3842 chip. It had gone completely open. It wasn't damaged or burnt, just like your one.

[@massimopessino7606]

Always great and very informative to watch your CRT repairs! Keep em coming 😊

[@NullReference119]

RE Dielectric grease: it's used in theory to keep the rubber of the cup from sticking to the tube. If you think it might do that, use it. Otherwise use best judgement.

[@wirtannen]

The moment you realize Adrian's labcomputer has the same background image as you had for years. LHC.

[@RetroHQ]

One of the most common failures for battery corrosion I've found recently has been surface mount resistors. Even parts which have visibily looked fine and have been on the other side of the PCB to the battery. So these days I always suspect resistors!

[@helmargesel3972]

Thanks for sharing your knowledge

[@IanFarquharson2]

Nice perseverance. It looked like some cap charging and knocking out the drive on the transistor after each pulse train.

[@thirstyCactus]

The higher cost of the CM-1 might be due to the lower dot-pitch CRT. I remember low dot-pitch being a premium cost.

[@andrewlittleboy8532]

I think the silicone grease on the cap is to help prevent any arcing.

[@movax20h]

Good troubleshooting. I think the mods on the neck board were to remove some of the high frequency edges to comply with the FCC in US. My guess. Also sometimes the high frequency content can cause some resonance and ringing (due to parasitic inductance maybe), which causes text to not be super sharp, and this maybe was a way to text look better. Probably not critical for TV, but important for a computer.

[@GalthimGaming]

The smallest repairs are the ones that take the longest. Also, Nice Mega Man 2 NES cart in the background!

[@GalthimGaming]

Actually, I should say Lanyard for a show with the art of Mega Man 2. :)

[@nrdesign1991]

1:05:08 in a parallel universe, it would be Adrian's Analog Basement slowly getting the hang of digital :)

[@CasualSpud]

Adrian's Analog Alcove

[@oliverer3]

​@@CasualSpudAdrian's analog attic?

[@nrdesign1991]

@@oliverer3 that should be his second format!

[@rommix0]

If it were the alt universe, digital would be hard to work with due to archaic copy protection lol.

[@storhemulen]

Very interesting! Thanks Adrian.

[@richardbrobeck2384]

Nice Repair Adrian !!

[@GGigabiteM]

I hate that circuit glue. I once had a Dell power supply where the manufacturer got the bukakke blaster 9000 of circuit glue and covered about 1/3 of the PCB in a quarter inch thick glob of the stuff. I spent hours having to chip all of the stuff out, and replace dozens of components that were entombed in it and had been corroded to nothing. I had resistors where the legs had been completely corroded away, and only left the casing. Once I started finding stuff like that, I had to slow down to an archeologists pace to avoid damaging components that I'd need to be able to read the values from. The reason I didn't replace the power supply is because it was proprietary, over a decade old, and any substitute I'd find would have the same problem.

[@benanderson89]

So essentially, there was nothing to drain the capacitor, so the smear was said capacitors natural voltage decline. I saw the ramp on the oscilloscope and I said "that'll be a capacitor not being drained properly" but I wasn't expecting a tiny resistor to be the problem.

[@patrickcraenen5163]

Hey Adrian, Thanks for another super interesting video! I've been a big fan of your videos for a long time. Very well done! You're sometimes a bit hard on yourself because you do it incredibly well ;-) I regularly watch repair videos from other creators where I often shout at the screen, I've never had that with your videos :-) Although you may say you have less experience with analog circuits, your technical insight and logical thinking always ensure that the problem is found. Thanks for all the passion, time and work you put into your videos. Take care! I'm already looking forward to the next video. Cheers!

[@horusfalcon]

That glue looks suspiciously like hide glue, which is still used by violin makers and luthiers. It is the "original" hot glue. No worries about camera issues - the important stuff was sharp and clear.

[@zero0ryn]

Yay, I got a mention 🎉

[@solarbirdyz]

The Tandy 2000s got incredibly popular amongst BBS runners when Radio Shack started clearing them out, because they were so capable and suddenly so cheap. They were also - as far as I'm concerned - kind of the last hurrah of Radio Shack/Tandy as a fully independent system designer, being as far as I know the last time they really tried to forge their own (and I'd say better) path. Really good machines, particularly given they were DOS based. It's just too bad they didn't do better in the market. (You may and may not consider the Tandy 6000 in that, but the 6000 was just a faster 16B, etc.)