• Please review our updated Terms and Rules here

Mac II video sync issues

NeXT

NeXT

Veteran Member
Joined
Oct 22, 2008
Messages
8,178
Location
Kamloops, BC, Canada
I pulled out of my pile a really nice apple branded NuBus video card that can display 16 million colors and also has two VRAM expansion simm slots.
The problem is that the sync is very erratic. It did have a light amount of corrosion which I washed off with distilled water however there is a single crystal on the board that at least feels loose even though it is soldered in place. It would be really nice if I could upgrade my Macintosh II to this card as to replace the original card but do you think that this one possibly damaged crystal might be the problem?

Also, speaking of Nubus, does anyone have a Nubus-based Photoshop DSP accelerator card handy? I have always wanted one for my old copy of Photoshop just to see how much better it makes Photoshop run an old 020.
 
Crystals

Crystals

NeXT said...sync is very erratic
Click to expand...
Horizontal, Vertical or both ?
Dumb question, are you sure your monitor can handle the card ?

Crystals & Crystal oscillators (the rectangular all-in-ones) are definately sensitive to strong shock. The two-wire ones usually come in sort of hollow oblong "can". You can actually cut the can apart if you're careful, and see the crystal. It looks something like this:
http://en.wikipedia.org/wiki/File:InsideQuartzCrystal.jpg

I don't know what card you've got, but usually the crystal drives the dot clock (in 10's to 100's of Mhz range ), and the sync would be derived from that, either directly or through the gpu. If it comes from a PLL, the crystal might be fine, but the PLL circuit faulty( which may actually be in the gpu ).
But if the crystal actually feels loose, I'd try replacing that first.

Does it look like a hassle to replace the crystal ?

patscc
 
Can you take a snapshot of the card? What OS are you using?

Some video cards will not work correctly in system 7+ because the ROMs onboard were for system 6 only. When Apple went to system 7 there was a huge rush to get updated ROMs out for older cards so they worked (Supermac comes to mind). Some probably do not work in system 8 at all (but then again system 8 needs an 68040 to install anyway).

DSP cards can be found on ebay every so often, I have a few but they are in use and not for sale.
 
Here are the photos.

PB082263.jpg

PB082264.jpg


It's currently running under system 6 and I *think* (and if I am wrong it's the opposite to what I say) it is vertical sync I have lost but like I said I have never really managed to tell the difference between the two.
 
when you lose vertical sync, the picture rolls (vertically). When you lose horizontal sync, the picture get wacked out horizontally ("tears", but to me that's hardly descriptive of what happens). Theoretically there could be a bit of vertical rolling w/the loss of hsync. But it's usually obvious what the problem is.
Is the monitor suspect? I thought the 2 terminal crystals could be unplugged (but then the receptacle could have a cold solder joint or be cracked)? The other type would be soldered in.
There's nothing scary about soldering. You can touch up suspect solder joints and sometimes be right back in business. I once had a p/s that was flaking out. I randomly *hit* a number of solder points on the underside of the board (had to remove it of course), and didn't even hit them all! The unit worked fine after that.
In reality it could be the monitor. I used to have a 48khz Sony Trinitron OEM that should have nicely taken a Mac's 832 x 624 mode, but wouldn't. I never actually diagnosed the problem, but I think it may have had something to do w/the sync pulse width or something. It really shouldn't have had a problem, but did. It wasn't an actual Apple card, an eMachines Futura IIRC.
Still have a 1/2 dozen old fixed frequency monitors in the garage. All Sony's.
 
Video & Clock

Video & Clock

NeXT said...really managed to tell the difference between the two
Click to expand...

Horizontal troubles:

picture.php


Vertical troubles:
picture.php


The rectangular shiny bit is a 100 Mhz oscillator, probably responsible for the dot clock. It looks mechanically sound, and if there's no water( see a bit further on ) or corrosion trapped beneath it...
The 20 Mhz crystal looks to be hooked to the DP8531 clock generator, which may drive a clock on the ramdac, the shift clock for the vram, don't know, I'd have to know more about the ramdac. There are boards where the sync is derived from a clock generator seperate from the dot clock, but locked via a PLL, so that 20 Mhz crystal & clock generator may actually be what sync is derived from.

Can you take a picture of the underside of the board, where the crystal is ?
Can you take a picture of the display ?
Can you try a different monitor ?
The crystal looks like it might have some corrosion on top. Is this true, or just the pic ?
You mentioned you rinsed the board with deionized water. SMT devices have a tendancy to trap water between them and the board at times. Are you absolutely sure the board is dry ?

patscc
 
In this case then it's probably neither horizontal or vertical and I know it's not limited to one monitor as two small mac monitors (B/W and color) show nothing at all, my projector tells me it's getting an unsupported signal and my 17" mac display is just barely picking it up but it's next to impossible to do anything on it due to the horizontal tearing and after a few moments the monitor kicks out as to not damage itself.

See for yourself.

P1010207.jpg


Also, the crystal I am concerned about is the one centered in the second photograph.
 
Noise or weak signal

Noise or weak signal

That actually looks more like noise or weak signal levels.
Are you sure that there's no water trapped underneath the chips ?
How did you dry it, by the way ?

patscc
 
Absolutely. whenever I wash a board (I have seen many motherboards go through the dishwasher, sans detergent of course) I then let it dry over a heating register or monitor (my IBM P201s give off a lot of heat) for at least a day before I even attempt to power it up.
 
wash behind your chips

wash behind your chips

tipc bubbled...maybe you should try a different brand of detergent
Click to expand...
Actually, that's not as far-fetched as it sounds. Distilled water has a rather high surface tension, which is why you add detergents to it, so the the surface tension ( and hence the capillary action ) is reduced, so it doesn't lodge between pins & parts as easily.
The trick is that if you start adding too much detergent, micro-clumps start forming, which cause all kinds of problems on their own.
Defluxing baths, if they're aqueous based (instead of some non-polar solvent), have detergents and additives to mimimize the surface tension issue.
The problem with deinozed water is you never know what you're getting unless you test it.
If you're unlucky, you'll have stuff with a resistance of about 200k. This can be responsible for pretty hefty creep currents (well, hefty as far as VLSI CMOS chips, anyway ) between chip pins.

NeXT, do you have a scope, by the way ? If so, you could at least check Vp-p on the video & sync lines and see what you get.

patscc
 
I honestly wish I had a scope.
I have wanted and needed one for years.
The most advanced tool I own is an ancient signal marking generator and I have never even used that.
 
NeXT said:
I honestly wish I had a scope.
I have wanted and needed one for years.
The most advanced tool I own is an ancient signal marking generator and I have never even used that.
Click to expand...

You can get scope cards on feEbay that hook up to the parallel port of a computer (I use an old laptop for portability) for less than a hundred bucks.

They aren't 100 MHz quad trace units, but, for most things, they work pretty well. I use mine, mostly, to hook up to my home-made curve tracer.

Hell, the circuit is so simple, with easily obtainable parts, you could make your own.

Hey, maybe I'll do a run of circuit boards for one.
 
Scope

Scope

NeXT said...I honestly wish I had a scope.
Click to expand...
Is there someplace up there where you might be able to pick up a surplus/used one ?
A basic dual-channel 20 Mhz job should get you started. I'd try to find one that still has a CRT.
I have a Tektronix 2235 & a Fluke ScopeMeter 97, and I like the bright CRT on the older 2235 much better than the LCD on the ScopeMeter 97.

patscc
 
patscc said:
Is there someplace up there where you might be able to pick up a surplus/used one ?
A basic dual-channel 20 Mhz job should get you started. I'd try to find one that still has a CRT.
I have a Tektronix 2235 & a Fluke ScopeMeter 97, and I like the bright CRT on the older 2235 much better than the LCD on the ScopeMeter 97.

patscc
Click to expand...

My high school used to (just my luck that right when I started high school they discontinued the course) have an electronics class and they have piles of HP scopes in the storage room but it will take a lot of persuasion for them to hand one over even though they are all destined for either the trash or the district surplus which the public are not invited to (business only).
There are no other places in town from which you can get a scope. You have to either travel to the coast or use ebay.
 
piles

piles

NeXT said...piles of HP scopes
Click to expand...
Tell them it'll help you repair their PC's or something. Or maybe tell them you want to start a extra-curricular electronics club, or something nice and community oriented like that.
If you get more than one, I got dibbs on the second one.

patscc
 
You must log in or register to reply here.
Back
Top