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Awesome! Yeah the 18khz/50hz signal you were seeing was the MDA scan-rate. The internal monitor on these is multi-scan and can run at either 15.6khz/60hz or the MDA rate of 18khz/50hz. Incidentally even though that scan converter says it can handle "CGA" it really means the 15.6khz scan rate... it's expecting an analog level input and no tthe TTL 5V signal that is coming from that card.

16:43 The menu says: 1. Image 2. Position 3. Display 4. Language .. Exit

A completed repair on the EEVBlog? Impossible!

Perhaps it needs to be in the case for all the grounds to tie-up? A 'chassis ground', so-to-speak..

3:07 Dave: Pat on the head Tantalum capacitor: :3

That GBS scan converter board is typically used in old arcade machines when changing them from CRT to flat screen. Used them a few times, with mixed results. It's cheap, but the more expensive ones give a much cleaner output!

The internal monitor is a different scan rate than the external 15K. The dip switches on the motherboard pick which kind of video card, not what video modes come out of the card. Hook to the 9pin for standard video signals and hit ctrl+alt+< for 15k.. Also, your keyboard is probably shot because of the foam going to crap over the years. (I rebuilt a compaq portable last year, including the power supply)

I worked with the guy who designed this machine. Back in the day.

My second work computer! Fantastic machine! :)

From what I can remember, negative voltages are for the tape and/or disk drives? Been a long time, memory gets hazy for that time period lol Great work, Nice vid.

Nice launch and belly-flop, but I was expecting more explosions at the end.

The composite issue looks like the same grounding problem I had a few months ago. Chuck in an ATX PSU and hook up a wire from Composite GND to PSU GND. Great vid , Dave. Looking forward to the next part.

Some older DRAM chips need +12 and -5 to work.

Only two days after watching the first video, someone in my apartment building dumpstered a November 1983 unit! It was the craziest coincidence I've ever had. I've disassembled it fully and tested the voltages on the power supply, but I'm apprehensive of putting it back together and plugging it in for fear of the tantalums going full nuclear. I've ordered a bunch of 10uF 25V replacements, but is there anything else I should watch out for? The unit came with quite a few upgrades, notably a multifunction 384K RAM expansion card and a 40MB Quantum HardCard. I'm eager to get this thing running, and I'll definitely be watching along!

I've had one of those GBS-8200 CGA2VGA converters back I'm 2016 for use with arcade boards. Since then, the video game community has turned it into a VERY competent scaler using custom firmware with some small tweaks/mods and an ESP8266 board to control it all via WiFi. The project is on GITHUB as "GBS-Control." I find it particularly useful since it properly handles 240p and consumer RGB (0.7v peak to peak, 75-ohm impedence) when it is very difficult to do anything with 240p RGB in NTSC land. :)

Well, the MDA and CGA are two different cards. MDA is a higher resolution monochrome card (max 720×348), while CGA is a lower resolution colour card ( max 640×200). You would need a different monitor to display an MDA card's output. We used to call the MDA compatible monitors TTL monitors, the CGA compatible monitors were composite monitors (cheaper), or RGB (More expensive!). Although, in theory, the MDA card could output graphics, it didn't so. The Hercules monochrome card, on the other hand, could output graphics at the 720×348 resolution. This made it very popular for doing CAD. After the Hercules card came out, it took over the MDA market...no one bought an MDA card...I think that the Hercules card was actually cheaper than IBM's MDA card. A very popular use for the Hercules card was for AutoCAD. In fact, it was that combination that made AutoCAD the defacto standard. Much in the same way today that we use Blender for benchmarking systems, people used AutoCAD on a Hercules card (or clone thereof) drawing the Firehose Nozzle as a good all-system benchmark.

You are a brave man to work on a Compaq portable. I remember working on those Compaqs back when they were still used and they were a nightmare compared to any desktop of the same era, as you have noticed. My "repairs" consisted of buying a replacement board and plugging it in, I never heard of anyone doing board level repair on those.

18:20 VHS mode: ACTIVE :D

I wonder if the composite video bouncing all over the place is related to the missing ground on its connector? Surely that should be grounded?

TO-3, now that's a device I haven't seen in a long time

Ah, the Compaq Portable - that was one fine (if heavy) machine. Portable computing and a nice workout in one package. ComputerLand (remember them?) sent me to the 2nd ever Compaq training class for techs down in Texas. Before I left ComputerLand I bought one with every conceivable option (and damn near everything was an option - like a serial port or even a clock card so you didn't have to type in the date and time on every boot). I think I had nearly $6K in that thing!

Super video

Dave, at risk of stating the obvious: didn't you have something plugged into the composite jack when it was grounded? :) If it was plugged into a display that puts 75 ohm across the composite connector, which is not a great ground but might explain what happened, if the signal leg was being driven to 0V

Thanks for this, Mate. I still have my Compaq Portable purchased as a Christmas gift in 1982. It's totally dead but now Dave has given me the urge to crack it open to see what's what. (If I can find it.) Dave --- I have a photocopy of the factory Maintenance and Service Guide. Lemme know if you want a copy. I also have both factory diagnostic disks but they're 5-1/4 inch so no easy way to dupe them.

when you showed aligator clips on power connector and said don't try this at home, I said I normally put temporary tape between them because eventually I bump something. Next shot, you've got the tape on there like I said 😁

EEVBlog Retro Computer repairathon =) Any chance you make retro stuff on a more regular Basis? :)

I know that +12 and -12 are used for the RS232 serial port.

Saw one of those Lugable PC at University of Nebraska at Omaha in about 1984 or 1985 in a Computer Science office area where I used an Original Macintosh. An Engineering Tech professor had an Osborne with tiny screen, and the Labs had IMSI computers with the Toggle Switched to Program them

In early IBM type PCs, the POST ran a memory test that had no visual output. Most people upgraded to 640K of RAM so when you flipped on the big red switch, it would appear to do nothing for over a minute while the memory test ran. There were many complaints about this so later PCs would show a memory count of the test on screen.

You should be aware that Compaq used a Dual-Mode monitor those days. That monitor can sync on either CGA (15.6kHz/60Hz, 200 visible lines) or MDA (18.something kHz/50Hz, 350 visible lines). The machine is replacing the CGA 80-column text mode with an 8x8 character box by an MDA 80-column text mode with an 8x14 character box, to achieve a significantly better text mode output. As the MDA text mode is quite different from standard TV timing, it's not surprising that it does not get synced. I guess the 40-column text mode is generated as genuine CGA text mode, and thus it works in this mode. The original (non-portable) Compaq Deskpro has a hotkey to switch between 350 and 200 line text mode, I think it was Ctrl-Alt-less/Ctrl-Alt-greater, which might work on this machine, too.

The ground shell on the rca jack might be broken, soldering it to the plate should snug it up

IC hook clips are great for these kind of power header connections when compared to alligator clips! Definitely my preference, usually easier to keep away from other pins and more secure.

3:08 is that a face drawn on that tantalum capacitor? a :3 face??

many early pc’s output diagnostic codes down the parallel port - so you can see what it’s doing before the screen initialises - i made a simple binary for hex decoder to get the code - 8 bit logic analyser will do.

IIRC -5v are needed for floppy disk controller op amps that control the disk heads on old/early floppy drives. [it's been 15+ years since I read that] [edit] this source mentions -5v for floppy and is routed through ISA card slots. A second poster mentions -5 for larger-than-64k ram (?!) by having onboard charge pumps ("4116" ram chips). [I can confirm that a 4116 datasheet does indicate -5v rail required.] electronics.stackexchange.com/questions/105064/what-is-the-usage-of-the-negative-voltages-on-a-pc-motherboard this post mentions -5v back bias for DRAM chips: electronics.stackexchange.com/questions/57368/why-is-there-a-12v-rail-for-atx also rs-232 serial ports DEFINITELY use +-12v rails.

2004 HP Compaq PSU seems like the then becoming obselete minus 12 volt rail was implemented the same way but through a surface mount LM 339 , sort of like a lock, I.E. PSU gets first say before mother board can send power good signal

Consider your self lucky: My IBM 5150 which I restored was dead when I got it. I had to replace all the buffer chips, Most oif the RAM & even the ROM as that had suffered bit rot. The last hurdel was the RAM dipswitches. But I was so happy when I got it to boot from MS DOS for the first time. Oh & there were RIFFA caps in the PSU, some did go pop.

Nice to see it's working.

amazing video

Love the repair vids Dave!

I have one of these plus a big box of 5 1/4 floppy disks. The only thing that doesn't work is the small CRT screen built in. The external VGA output does work which is how I've used it to test everything. Have no idea what I'll do with it...

I think the hdd floppy controller card needs the -5 and -12 volts....

FYI? Seen Fran, playing with one of your EEV BLOG Meters on her latest video... Your Famous!! Dah Dahhhh

-5 and -12V are usually used in peripheral cards. For example -12V is necessary for RS-232C to work properly.

I used to repair those and there is a "special tool" to remove that power supply screw

Composite output only works with certain video modes on CGA. I haven't used one since elementary school back in the 90s, but I vaguely recall that it worked fine in 40 column 320x200, 80 column 640x200, but not in the normal high(er) resolution mono text mode.

All this is vastly over my head but I love your accent haha.

I just fixed one to, and it also took me off in a wrong direction for a while, that it don't print anything on the screen for a loooong time.... but the original IBM PC also don't do this... it's first the IBM XT, which output's memory counts at start up.... Mine also contained a 'hardcard', and from the files, and dates, it seems it hasn't been used since 1987.....

Is that scan converter at 17:40 any good? is it one of DIY-kits or make it your self? second question why was displaying green text and not blank and white signal on the screen, like the out from the Compaq Portable when it was connected?

Either the -5V or -12V would be used with the DB25 RS232 serial port. I'm not sure why both would be needed but this could be an 'off the shelf' PSU providing more outputs than necessary. ETA: Only needed for your 110 or 300 baud acoustic coupler, LOL.

If the components and the settings check out...If you have continuity, throughout the system, it will usually work as designed?

Hi Dave, I don't know if this was pointed out or matters: The first time you connect it by composite and get it to work, I believe the TV info bar at the bottom said NTSC (18:20), shouldn't it have been PAL?

The graphics card and monitor should be Hercules compatible also. I put a 25MHz 386 motherboard into one of these back in the early '90s. I had to rip out the 16 bit extension of one of the ISA slots so the original graphics card would fit. Also had to modify the power connector to be AT compatible. I installed Windows 3.11, but had to make up a driver disk because Hercules wasn't natively supported (got the files from an older version of Windows). The disappointing thing was XT keyboards are not compatible with AT PCs so the keyboard had to be replaced and no longer fitted into the front of the case. If it was my machine I might have hacked an AT controller into the XT keyboard, but it was for someone else who didn't care. [edit] The Hercules scan rates used by that graphics card in most modes are probably why only the 40 colunm mode works with the converter and external monitor.

The reason it takes time to boot its performing a POST power on self test, memory ,drives etc

لغتك جميلة اتمني ان اتعلمها ويعجبني جاهز الاسلسكوب رائع شكرا لك♥

Sweet! 🤘😎🤘

On my Portable II the 601 error was from the bios battery being dead. I replaced the battery and configured bios and it went away.

is it hard to build demo/test stand for core memory module? please can you help in developing one?

When you were showing the powersupply it looked like there was a loose connection from the transformer

whats a reefer cap? what material does it use to store charge?

The board you're using (GBS-8200) is known to be pretty crappy, however there has been a community effort to enhance the stock program, especially for retro computers and consoles. For the price, the scaler chip is actually very powerful, but stock implementations are terrible. github.com/ramapcsx2/gbs-control

The video card connector was getting it's ground from the case.

But why is the composite jack not grounded?

- Mom, can we have part 1? - We already have part 1 at home. Part 1 at home: Part 2

With how popular those GBS8200 CGA/EGA/YUV converters are, you'd THINK they'd support the 18.4 KHz sync pulse used on these MDA cards.

Might I make a suggestion? Why not fit a Mean Well PSU in the system if the original really goes haywire. It seems like it's half dead at this point and the floppy controller uses one of the negative rails iirc.

Blast from distant past, haze 300bps carried one of them to class and used it to `take notes, in class. Lotus 123 anyone, miss that, It is late, and I can here the bar from hear. kbps vs Kbps ha, be safe out there!

if i find one dry joint i sit back heat up the iron and re solder one by one the whole board find it almost therapeutic

Look at: *CR52*

getting composite video from CGA/EGA cards to work on modern LCDs is very hit or miss. The signals on those cards weren't exactly designed to NTSC or PAL specs, so you need a real tube with its loose tolerances, a forgiving TV, or a good converter. If you're going to continue with this repair, I'd recommend investing in an old Trident TVGA9000i ISA video card. They're 16 bit, but have 3 jumpers that can be closed to force 8-bit mode operation, and will work great with these old computers on modernish monitors. I still have a functional 8088 Turbo PC that uses one.

Dave, I love your alligator (Crocodile) clip set, in this video. What are they?

Even my turbo pc dont have an open power suply lol

Isn't the Neg power for UART devices, for driving RS232 type ports

Your bench PSU grounds are isolated, aren't they? Maybe the (analogue) ground reference for the video circuitry is not the same ground as the bracket/digital ground. That would be a really dumb design, pushing the ground path through the PSU wiring, but it would explain why it worked a couple of weeks ago with the defunct PSU but not with the bench supply today.

The bigger question, can i play Cyperpunk 1980 with it?

And Dave is not even taking part in #DOSCember

i think there is some powersupply data in the service manual and am 95% sure the sams computerfacts for this machine has a ps schematic

I beleive the terminology is "Focus you Faaak" Dave. LOL

Great to see this machine coming back to life! I’ve been following along with mine. Would you be willing to share the pinout of that internal CGA connector? I lost the original video card, so I have no way of connecting the internal display. But I do have other CGA cards I could modify to add an internal header with the right pinout.

That psu dosent look thought out very well

Is it possibly an ntsc composit signal?

they ground through the case and mains ground

Hey Dave (and youtube), I know it's probably a bit late to ask but I'm curious if you could suggest some Christmas gift ideas for the electrical engineer that performs reverse engineering, schematics, and fpga programming. I was thinking of a vise...Or perhaps a digital caliper. Thank you!

COMPUTERS OFTEN MAKES PEOPLE ANGRY QUITE

The traces on the back of the power supply board look odd, almost like they're delaminating from the layer beneath them. Since it's not mentioned in the visual inspection I assume it's not a functional issue, but I'm wondering what's going on there. Is that normal for older boards?

Looks like a cracked joint around 5:30

Hey guy, you set a bad example, I mean, your crocodile clips!

Что за блок питания на 4 канала?

That is your pc

I don't think I've ever seen a part origin marked Britain like that TO-3 is, didn't know they ever exported any semiconductors at all!

I lusted after that PSU until I googled it NGP800 = starting at £2430. Nope, but just for reference here are the specs www.rohde-schwarz.com/uk/product/ngp800-productstartpage_63493-670592.html

It's only me who noticed :3 face on C37 (bottom right corner)? ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-4XGwveNyLJo.html

Davies New saying " one of time things"

I've got that motherboard that I was never able to get working...

For anyone else buying hardware with chinese menus 英語

Wouldn't the bracket on the video card be grounded through the chassis?

chassis grounding !

This is what the DIP Switch does: Switch | Function ---+----------------------------------+-------------------------------------------------------- 1 | Reserved (always off) 2 | Numeric coprocessor | Off: 8087 installed | On: No 8087 3,4 |Memory size | Reserved (always off) 5,6 | Initial video mode | Both on: EGA | 6 on, 5 off: CGA 40 | 6 off, 5 on: CGA 80 | Both off: MDA 7,8 | Floppy drive count | Both on: 1 | 8 on, 7 off: 2 | 8 off, 7 on: 3 | Both off: 4 -----+-------------------------------+--------------------------------------------------------

is using the case as a ground

I own a thinkpad from the 90´ with similar error codes and in my case it´s a friend superio chip causing this problem.