Apple //e picture issue

[Tony359]

Greetings all,

 

My first post here.

 

I've acquired a 1982 PAL Apple //e - motherboard 820-0073-A (with a B stamped underneath, same as here: https://atariage.com/forums/topic/304447-graphics-corruption/?tab=comments#comment-4492557) which is working but it has a graphic issue: there is a vertical line missing every "column" - see attached pictures, in text mode you can see that on the inverse text. So I have 40 black vertical lines when in 40 columns mode and 80 black lines when in 80 columns mode. 

 

I am still familiarising with the circuitry of this thing so I'd appreciate your help. I poked the video section with my oscilloscope and I did not find anything obvious such as dead or stuck data lines on the Video bus. All lines seem to have continuity. I have reseated all the relevant chips - LS324, IOU, 2732. LS166. Someone on another forum suggested the RAM: all software I tried say RAM is good but I went ahead and shifted the RAM chips by one position. The line did not move one pixel.

I found evidence on another forum that it could be the Video ROM - I have a ROM writer coming as I need it for other projects too.

 

Any ideas? BTW, can you possibly confirm that the "2732" mentioned in the schematics is the Video Rom? I found the description to be not entirely clear.

 

Thanks a lot!

Tony

[GameGeezer]

I posted replies to you on AF. I've no need to duplicate them, here.

[Tony359]

Of course and thanks for your help!

[Keatah]

Useless thread.

 

[Tony359]

why is that? 

 

Don't you think you're being a bit aggressive guys? I'm just asking a question and I believe I did that politely and giving plenty of details.

[The Usotsuki]

His attitude is "why not just emulate?"

[Tony359]

whose attitude?

[ChildOfCv]

Sounds like you're getting help on Applefritter, but the most plausible cause appears to be the 74ls166 chip.  It's a parallel-load shift register that pushes pixels out 1 bit at a time.  Obviously if one of the parallel load input lines is dead, you'll get a stripe every 8 pixels.  If you checked all the inputs to this chip and found them all alive, then it pretty much has to be the problem.

 

If you mean you just took a brief look at a few data lines, then do the above check of all LS166 inputs.  If any are dead, the 2732 is the next likely culprit.  If they're all dancing gleefully, then like I say, the 166 has to be the problem.

[GameGeezer]

7 hours ago, Tony359 said:

why is that? 

 

Don't you think you're being a bit aggressive guys? I'm just asking a question and I believe I did that politely and giving plenty of details.

 

My apologies if I sounded cross. I wasn't. I just do not feel up to cross-posting all of that diagnostic information. There is nothing wrong with asking for help from different venues. I posted here, primarily, to indicate that I was not ignoring the thread, but rather, to indicate that I was rendering aid elsewhere. 

Edited June 22, 2020 by GameGeezer

[Keatah]

8 hours ago, The Usotsuki said:

His attitude is "why not just emulate?"

Incorrect. Useless because the solution was being posted elsewhere.

 

[Tony359]

First of all, apologies for cross-posting. I know this is not good on the same forum but I thought it was ok on different forums. By doing that I didn't mean to imply that I do not trust AF's users of course, I just feel that the more the voices the better: as you can see I'm now getting more options for my issue.

 

GameGeezer, I am not sure who you are on AF but thanks anyway for your help and of course I don't want to duplicate information here. I appreciate I should have at least mentioned that the same info was posted on AF. No apologies necessaries!

 

ChildOfCv

I have checked 166 again and yes, I have data on all input Video lines. I put Copy II Plus on screen and I while I was moving the inverted text up and down, I could see a cluster of "zeros" moving on my scope screen. Which is a bit puzzling as you say: as one vertical line is not drawn, I was expecting NOT to see data on at least one line. I am probing on the top of the leg of the chip itself so it cannot be a bad contact. Indeed I feel you are right and the 166 could be skipping that line when it's making the serial data out. I believe I can find that chip online, brand new. Shall I order the LS or HC version? I believe LS which is 5V supply (HC is 2V)?

 

Also, is the PAL HAL supposed to be 20C warmer than any other chip on the board?

 

Again, thanks all for your help, I hope we can all be virtual friends!!

Tony

Edited June 22, 2020 by Tony359

[Keatah]

It is not rude to ask a question in multiple forums. It is rude to say there is no need to post the answer here.

 

 

[ChildOfCv]

1 hour ago, Tony359 said:

Shall I order the LS or HC version? I believe LS which is 5V supply (HC is 2V)?

It's often best to replace in kind.  For instance, HC (which actually allows much higher VCC's) or HCT (the TTL equivalent built with CMOS) may use less power and run cooler.  But the difference in propagation delay or drive current may cause unexpected pixel smearing.

 

Of course you could buy one of each and a socket, so that it's easy to do side-by-side comparisons.  They're probably only a couple of bucks per chip anyway.

[Tony359]

On my board every chip is socketed. I understand it's a peculiarity of early PAL boards so I'm in luck

The current 166 chip doesn't show any LS or HC, I'll do a search tomorrow and see if I can find more info. 

Thanks for your help so far

[ChildOfCv]

Oh I see.  Euro Apples used a 74166 instead of the LS.  I wonder why?  Looks like it can source about .8mA, sink 16mA, and has between 35-40ns propagation delay.  LS is similar but slightly slower.  74HCT166 can source or sink around 25mA but has up to 20ns propagation delay.

 

HCT may be worth a shot if you can't find a straight 74166 (TI, among others, consider the straight number obsolete).

[Tony359]

ahhh - bugger. Well, I have an LS coming, I shall try that but I've also found some 74166N on Ebay.

Cheers!

[Tony359]

Today I received the LS166 - I gave it a go and... it worked! No more black lines at the end of each text block! I have a proper 166 coming but I couldn't resist!

 

Thank you all so much, ChildOfCv in particular!

 

Now I need to sort out the unstable picture - particularly when in colour mode. I believe I can play with the controls in the video area - the variable capacitor close to the oscillator and the two trimmers. Is there a more scientific way to adjust them or do you just play with them until it gets better, if it gets better? I couldn't find any instructions on the technical documents. 

(First I will mark their position of course - or even better I'll try to take a reading of the resistance and the oscillator amplitude.)

 

I'll make some videos so you can get an idea.

 

Thanks again!

[Tony359]

Here is a link to a video. This is in B/W mode. In Colour mode it seems ok but every now and then it pulses red which is quite obvious when in text mode. It seems to happen randomly, sometimes it keeps happening and sometimes it's ok for a while - I couldn't catch it on video tonight. The issue when in B/W instead (which is probably not too relevant 'cause I'm not going to use that with my LCD, only with the Apple monitor) happens all the time.

 

 

[ChildOfCv]

Is the stability a new issue since installing that chip?  Or has it always done that?

 

Also, it appears to be shifting by entire character widths.  Do you agree?

 

If so, then that may be the HAL chip.  You mentioned that it heats up.  60C is not death to a chip, but it definitely shortens its life.  You could get a can of compressed air to blow on it and see if the stability improves.

Edited June 24, 2020 by ChildOfCv

[Tony359]

No, that was a pre-existing issue. I am not sure it's being shifted by one position - I feel it's the monitor not locking somehow. I have watched carefully and it doesn't seem to move one space - more like 1/2 or 3/4. 

I have tried cooling down the HAL but it doesn't seem to improve. I'm ok with 60 degrees on a chip, it's just that it sticks out of the board as no other chip gets so hot.

 

I've managed to catch on video the red blooming - that happens when in colour mode, text mode. It almost looks like it's linked to the drive activity - and indeed it stopped after the drive stopped - but then it did that again when the Apple was idle so I think it's just a coincidence.

 

 

[ChildOfCv]

Have you tried it on a TV or other composite monitor yet?

[R.Cade]

Yeah there is no way to really know if something is wrong when connected to LCD. It usually does wacky things.

 

[Tony359]

Yes, on a proper old SONY LCD TV and I could see the red flashes there too. Now, I know these are not CRT TV's but I do see lots of videos online of Apple showing fine on LCD's so I assumed something is not right with the signal? 

[ChildOfCv]

6 minutes ago, Tony359 said:

Yes, on a proper old SONY LCD TV and I could see the red flashes there too. Now, I know these are not CRT TV's but I do see lots of videos online of Apple showing fine on LCD's so I assumed something is not right with the signal? 

The red flashes may be PAL encoding issues.  But I was currently concerned about the shifting screen.  If that doesn't happen on other CRTs or TVs then I'd conclude that it's the Apple Monitor.

[Tony359]

The shifting screen happens in B/W on an LCD. It's fine on my Apple green phospor monitor. To be honest, since I will never use the B/W on an LCD, maybe we don't have to worry about that - but it may give us some clues on what's wrong.

 

Please note that what you see on the videos is on a DELL LCD monitor with proper composite input.

 

Are you aware of any instructions on how to tweak those four adjustments for video output? I've read about tinkering with them while looking at the video but nothing more.