Any guesses as to the failure? - Page 1
Forum section: electronics / general

author: alank2
author_rank: Super Contributor
timestamp: April 22, 2017, 09:50:10 pm
content: There is a guy selling 7 original compaq portables - he says they all have the same failure - that the CRT does not work. I would be interested in having one, but only if I could have a reasonable chance of getting the CRT working. Any guesses as to what might be the failure? Especially since all 7 of them have the same failure point. I guess there were 9 originally, all with the same failure.

author: Rbastler
author_rank: Frequent Contributor
timestamp: April 22, 2017, 09:57:47 pm
content: My guess would be that something so wrong with the line transformer itself or the circuit powering it

author: tautech
author_rank: Super Contributor
timestamp: April 22, 2017, 10:16:05 pm
content: Portable with a CRT ?If they use and LCD type display the backlight failure would be my first suspect....easily checked with a bright light shone on the display while powered on.

author: alank2
author_rank: Super Contributor
timestamp: April 22, 2017, 10:18:25 pm
content: Yep, CRT. This is like the _first_ portable, if you can call it that! Built in 8" or 7" CRT...

author: Wimberleytech
author_rank: Super Contributor
timestamp: April 22, 2017, 10:50:21 pm
content: If you are referring to the first Compaq, I can tell you this. The power supply board was notorious for going out. I owned one and replaced the power supply board twice.

author: tautech
author_rank: Super Contributor
timestamp: April 22, 2017, 10:57:10 pm
content: CRT failures could be something quite simple like:Heater supplyEHT supply. LOPT ?HV supply for the deflection plates (if used) or drive of the deflection coils.

author: SeanB
author_rank: Super Contributor
timestamp: April 23, 2017, 12:03:04 pm
content: CRT does not work, likely you have dead capacitors in the power supply, the monitor board also has some dead capacitors, a few high value resistors in the CRY bias have drifted high, and the 2A fuse on the board is blown because of dry joints on the LOPT base and the scan coil plug. Other than that a dead line transistor because of the dry joints, or dry joints on the line driver transformer or the base pull down resistor across the driver secondary. Beware of low value high voltage electrolytic caps there, they can go open circuit or very high ESR, and give odd symptoms.Not too hard to fix those, done a few in the past, and the board layouit will be similar amongst all the assorted chassis variants they used. Still have one at work as a spare CRT display for a camera, Panasonic and still works well, though the tube is getting a little tired.

author: tooki
author_rank: Super Contributor
timestamp: April 23, 2017, 12:09:25 pm
content: Quote from: tautech on April 22, 2017, 10:16:05 pmIn the early days of PCs, "portable" meant an all-in-one that could be carried (nobody said comfortably!) and easily transported in a car. The first Mac, for example, was a portable, at "only" 17lbs. Same with the original Compaq, the Osborne, etc. Most of these didn't have a battery option, they were mains powered. They also predate dot matrix LCD screens, so they used either CRTs or monochrome plasma displays.The term "laptop" was invented to mean something more portable than a "portable". "Notebook" in turn meant smaller still.

author: Shock
author_rank: Super Contributor
timestamp: April 23, 2017, 02:43:29 pm
content: Quote from: tooki on April 23, 2017, 12:09:25 pmWell actually close, Portable was the marketing name used by the Compaq and the IBM for those desktop PCs with CRTs built in. The words laptop and notebook were coined really really early on and the same form factor as each other. More definitive is when tablets and netbooks started was many years later.Edit:Actually well over a decade later some companies marketed laptops saying they are specifically notebooks. But you got to remember laptops back then started tiny as they couldn't make huge screens. When they started making cheap behemoth screens the high res small screens became niche, hence notebook made it's second coming. Geography made a difference as well.Also the Compaq wasn't the first portable either. I believe according to the documentary I watched they said the first overwhelmingly financially successful one. I was around then but you had to have some nice spare cash to buy these new. You could buy a whole computer now for the cost of a floppy drive back then.

author: alank2
author_rank: Super Contributor
timestamp: April 24, 2017, 12:00:47 pm
content: The seller and I have agreed upon a price - hopefully in a week or so I can do a teardown with some pictures and we can start looking at what might need to be fixed!

author: tooki
author_rank: Super Contributor
timestamp: April 24, 2017, 06:42:55 pm
content: Quote from: Shock on April 23, 2017, 02:43:29 pmPlease don't gratuitously quibble with me — a computer history buff — about terminology distinctions that contribute nothing to the discussion. I was helping another member understand why a CRT-based computer might be called "portable", and your reply only takes away from the clarity I provided.

author: Shock
author_rank: Super Contributor
timestamp: April 24, 2017, 08:25:56 pm
content: It's my civil duty to add ambiguity to any thread I see with posts from proclaimed computer buffs.

author: bitseeker
author_rank: Super Contributor
timestamp: April 24, 2017, 10:16:18 pm
content: Quote from: alank2 on April 24, 2017, 12:00:47 pmLooking forward to it. It's fun to see these once-referred-to-as-portable PCs.

author: alank2
author_rank: Super Contributor
timestamp: April 28, 2017, 02:58:26 am
content: Well, it arrived, and it looks pretty, but it has been a bear to get running.The power supply would come on for a second and then shut down. I discovered the +12V rail was shorted. I found the short (bad tantalum cap) on the main board and replaced it with an electrolytic. Feeling pretty good, I plug the video card back and and it was shorted again! Another bad tant on the video card needed replacement too. Finally got the PS to stay running and saw the familiar blinking cursor!!! Then it came up with a floppy disk error and displayed some text. The monitor is at least working well. Tried a few things with the floppy controller and was probing it a bit when I discovered a 16 MHz oscillator was not oscillating! I had a spare so I changed that out and that fixed the 601 error, and finally it seems to be trying to access the floppy now! Whew. Then I discovered the keyboard doesn't work.... It is the capacitive pad type and I took it apart thinking the pads were disintegrated, but oddly they don't look that bad, they just don't work. If I touch the pcb pads with my finger, it does however work and will type a key and cause it to hit the floppy drive again to look for a disk. I don't have a bootable disk yet because the guy forgot to ship it, so the no disk message is all I can see on it.Here is my post at the vintage forum with more detail and a picture of the keyboard pads:http://www.vcfed.org/forum/showthread.php?57414-Compaq-Portable-12V-rail-on-motherboard-is-shorted&goto=newpostThanks!

author: helius
author_rank: Super Contributor
timestamp: April 28, 2017, 03:04:14 am
content: There are people making kits to restore the capacitive keyboards.http://www.ebay.com/itm/Victor-9000-SIRIUS-1-Keyboard-repair-Foam-Pads-for-KeyTronic-Keyboards/121266887970

author: alank2
author_rank: Super Contributor
timestamp: April 28, 2017, 03:07:15 am
content: I sent one of them some questions.Is it the part that touches the PCB that activates a key (it looks like a plastic circle), or the disc on the other side of the foam, away from the keyboard?

author: helius
author_rank: Super Contributor
timestamp: April 28, 2017, 04:01:24 am
content: The metal foil that makes the other capacitor "plate" is above the foam. When you press a key the foam compresses and the "plates" get closer, increasing capacitance.

author: Shock
author_rank: Super Contributor
timestamp: April 28, 2017, 12:23:15 pm
content: Hopefully you dodged the CRT burn in bullet.Remember the golden forum rule as well, photo or it didn't happen.

author: alank2
author_rank: Super Contributor
timestamp: April 28, 2017, 12:32:25 pm
content: Quote from: Shock on April 28, 2017, 12:23:15 pmI did, the screen looks beautiful.Quote from: Shock on April 28, 2017, 12:23:15 pmI'll get some done later today - the odd thing about this machine is that it looks so clean. Even the circuit boards look clean! Wherever it has been for the last 30 years, it was away from dust and dirt.

author: vealmike
author_rank: Regular Contributor
timestamp: April 28, 2017, 01:05:53 pm
content: Quote from: Shock on April 24, 2017, 08:25:56 pmEdited for accuracy.

author: Shock
author_rank: Super Contributor
timestamp: April 28, 2017, 03:12:31 pm
content: Quote from: alank2 on April 28, 2017, 12:32:25 pmSounds like it has low hours, could have been shelved after it was seen to be faulty. I'd keep an eye on it and give it a good graceful run in. Turn down the CRT and disconnect the cable if your scared of burn in. Common for caps to go bang after its been running.Every single version of dos is on the web you just need to look for them.Once you get a keyboard running download a game like Hack and use this machine like it was intended.http://www.abandonwaredos.com/abandonware-game.php?gid=1731

author: alank2
author_rank: Super Contributor
timestamp: April 28, 2017, 03:55:42 pm
content: Pics!

author: alank2
author_rank: Super Contributor
timestamp: April 28, 2017, 03:57:50 pm
content: Quote from: Shock on April 28, 2017, 03:12:31 pmI have no bootable diskette, but am waiting for one to arrive, so all I can see for now is "insert diskette"!

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: April 28, 2017, 04:54:58 pm
content: That's a beautiful PC. The CRT is white, green or orange phosphor? Somebody gave me a dead backlit Mac Portable (the first model) with a lead-acid gel battery that's been in my to-fix list for years (and still is).

author: helius
author_rank: Super Contributor
timestamp: April 28, 2017, 05:07:13 pm
content: I believe the Compaq Portable, Plus, and II screens were green. The IBM Portable screen was an amber CRT.Compaq used a red-orange plasma display for the Portable III. Some laptops also had those.Edit: the really spectacular luggable from that era was the HP Integral PC. It had a built-in full-size inkjet and ran Unix!

author: alank2
author_rank: Super Contributor
timestamp: April 28, 2017, 05:16:17 pm
content: It is green and it has a long persistence as well!

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: April 28, 2017, 08:15:25 pm
content: Quote from: alank2 on April 28, 2017, 05:16:17 pmWow, awesome, that's cool! The longest persistence I've ever seen was that of the original IBM PC green monitors, those with the cast metal enclosures that weighted tons, more than a second perhaps two or almost, it was amazing.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: April 28, 2017, 08:18:20 pm
content: Quote from: helius on April 28, 2017, 05:07:13 pmThose were amazing too!

author: james_s
author_rank: Super Contributor
timestamp: April 28, 2017, 09:18:44 pm
content: I used to have one of these, I kind of wish I'd kept it, I even had the matching padded carry bag for it.They have a 9" green CRT monitor that uses CGA scan rates and appears as a CGA monitor to the system. It was quite nice as I recall, very crisp picture.

author: SeanB
author_rank: Super Contributor
timestamp: April 29, 2017, 02:27:38 pm
content: I forsee a Schaffner input filter change will be a future thing, they will go bang after no power being applied to them for a few years.

author: alank2
author_rank: Super Contributor
timestamp: April 29, 2017, 05:40:26 pm
content: Quote from: SeanB on April 29, 2017, 02:27:38 pmWow, you guys are impressive. Yes, this happened. It began to make some fizzle noises for a day or so and I wondered if it was just a loose connection or something. Last night = loud fizzle and quite a burnt smell!!! It does seem to keep working though after that event, at least it is usable.

author: james_s
author_rank: Super Contributor
timestamp: April 29, 2017, 08:55:44 pm
content: If you have trouble finding a bootable disk I can make you one, I still have one XT in my vintage computer collection. Sounds like you might have one on the way already but thought I'd offer in case you don't.My Compaq Portable had a 10MB hard drive in it and that worked fine, although the power supplies in those machines were known to be marginal. I think if I had one now I'd install an XT IDE interface and small SSD or a Microdrive in a CF to IDE adapter.

author: alank2
author_rank: Super Contributor
timestamp: April 29, 2017, 09:00:20 pm
content: Thanks James - I appreciate it. A friend of mine actually had a 5.25" box of old disks and one of them was DOS 3.30! Once I had that I was able to create new disks and used fastlynx to move files across to create the other disks I needed! I ordered one of the XTIDE kits with a 128MB disk on module to plug onto it!

author: PA0PBZ
author_rank: Super Contributor
timestamp: April 30, 2017, 09:31:40 am
content: On topic (I guess): I just watched "Silicon Cowboys" on Netflix, recommended if you are interested in the rise (and fall?) of Compaq.