Re: Vertical Hold problem

From: Ray Arachelian <ray_at_email.domain.hidden>
Date: Tue, 30 Aug 2005 09:22:11 -0400

Be very careful when working on the video side of the Lisa - if you've never worked inside a TV, stay away, it's very dangerous. (working inside a Lisa is a bit easier than inside a TV though) - Standard warnings apply - You could be killed or shocked, etc. (standard precautions apply, don't sue me if you get shocked, you were warned, these technical procedures are provided for entertainment purposes, kids, don't try this at home, etc.)

That said, should you wish to continue, I'd highly suggest unplugging the Lisa from power for a few days to discharge whatever is stored up in the capacitors before attempting such work. I'd also remove all the cables from the Lisa such as mouse, keyboard, connections to a Profile hard drive, etc.

Tricks to prevent yourself from completing a circuit, such as working with one hand behind your back are useful here, so you don't electrocute yourself. An static wrist strap might not be a good idea as it will help complete a circuit, thus shocking you, so as a precaution to the sensitive electronics inside the Lisa, don't touch any of the boards other than the video board.

Wearing rubber heeled shoes for insulation is a great idea. There is also a small danger of X-Rays from the tube, but since you're not going to stay close to the tube too long, I wouldn't worry too much about it.

Worry about the tube being very fragile and breakable, make sure there's nothing that can fall on top of it or be dropped over it - if it shatters, it will implode and send lots of sharp heavy glass shards everywhere - wearing eye protection is a good idea just incase this happens. (If it does, you lost your Lisa as you're unlikely to find a replacement tube for it.) Worry about the high voltage, and currents. If you can wear a glove on the hand you'll use to adjust the settings, don't touch anything with the other hand that could be act as ground (i.e. the table, any metal parts inside the Lisa, etc.)

You'll have to remove the back cover, then the top cover. Once you've removed the top cover, you can access the video board which is behind the CRT. The CRT's are quite fragile, so be very careful not to drop a screwdriver on top of it, or for that matter anything else. If you can, find a plastic screw driver, or something you can use in it's place - the video board has several sets of pots which can be used the adjust the vertical size, and vertical hold. Likely some component has gone a little bit bad or the pot itself has oxidized and isn't making a good connection, but you might be able to adjust one of these pots to fix it. Some may have some glue over them as a seal which you'll have to break in order to adjust.

Also look for a screen modification kit, you'll know you have one by the ROM version or by the existance of a transformer between the CRT cable and the video board. If you see this, it's a modified Lisa that will have square pixels and will not run Lisa OS, only MacWorks. You could remove this transformer, but you'd also have to get a set of replacement ROM's or CPU board. The normal Lisa OS capable ROM's are versions F-H (you'll sometimes see D, though I'm not sure if the D ROM will be able to work with OS 3.x) If you see a two character ROM, it's likely the video size modified ROM. i.e. "AA" is not what you want to see.

Once you get the display working, you'll know the ROM version for certain, it'll be displayed in the upper left corner on the menu bar as the Lisa POST works. It'll be something like H/A8 or H/88 - the H is the POST ROM version, if you see AA/88, you likely have a video modified ROM. The 88 is the I/O ROM which lives on the I/O board along with the 6504 I/O CPU. The two versions I've come across are 88 and A8. Some of these support 800K floppies, If you ever come across a 40 or 44 or any I/O ROM below 80, hang on to that, it likely came from a Lisa 1 which had Twiggy drives, and is valuable - it won't work with a 400K floppy, but it will be worth some money.

It's important to note the positions of all of the pots on the video board, incase you go too far and have to reset them to their normal values.

If I recall correctly, the back cover has a little bit of plastic that sticks out - when it's closed, it mates with a somewhat hidden switch that cuts power whenever you open the back cover. I think it's over the power supply if I remember. Once you familiarize yourself with the video board and the other insides of the Lisa, and are sure you're safe, you'll have to plug up that hidden switch with something - a small piece of cardboard will do.

You can then plug the power cable back in and power up the Lisa - then carefully insert your hand and the plastic screw driver, and adjust the vhold/vsize pots. Do it very very slowly.

(If you know how to get into service mode, perhaps you'll want to plug the keyboard and mouse in before you power on the Lisa as there's an option in there to display a square grid - that way you can make sure the size aspect ratio is correct. I believe once the boot menu comes up you need to tell it to boot off a floppy but not insert one, then hit Apple-S or Apple-Enter - the one on the numeric keyboard. Haven't done that in a while, sorry. You could also boot LisaTest if you have it to test your video display - it also has display test patterns which you can use while adjusting the video board's pots.)

Once you're happy with your change, you can hit the power switch and once the display is off, remove the bit of cardboard holding the hidden switch down, then close the covers back up, and turn the Lisa back on - hopefully, it'll hold it's new settings - otherwise, you may have to figure out what's bad on the video board and fix it, but that's a much more difficult task.

Mike wrote:

> Hello, I have been a lurker on this list for a good while now,
> picking up little Lisa pieces of information from time to time. I
> haven't posted before because I didn't own a Lisa, although the hunt
> was definitely on ! I have been lucky enough to get two Lisa's very
> recently. First impression: aren't they big ?! Photographs don't
> really convey the size.
> One Lisa is missing several parts which I am working on acquiring, the
> other Lisa (a 2/10) powers up just fine, however there is a problem
> with the screen, looks like the vertical hold has 'gone'. I have
> never worked on a Lisa before, but have a dozen or so 68k Macs that I
> have restored, so I know my way around old Apple products in general.
> Could anyone offer any tips or places to start to address the video
> issue ? The display is readable, but is repeated down the screen
> three times, with lots of flicker, and a bit of scrolling too.
> Many thanks
> Mike

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Received on 2005-08-31 08:26:29

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