Apple II Europlus video output

[zippysticks]

I'm really glad that all the IC's in this machine are socketed....

Strange video output on this Europlus. The machine seems to work in every way (starts up, beeps, responds to keyboard, loads and runs files from disk etc.) but has a messed up video output - see picture.
The screen appears as two replicas vertically with a squashed version of the characters displayed in both halves of the screen.

I'm working my way through the video section of the repair guide but its slow going - anyone seen this before ?

Interestingly, this machine came with a Videx videoterm 80 column card that when installed in this machine and its output switched on (in slot 3) using PR#3 , the 80 column picture view is superb.
I'm not quite sure how much of the onboard video circuitry is replaced by this card to narrow down my fault finding. I suppose its possible its a RAM issue too of course, but difficult to run the RAM test disk with this screen corruption.

By the way, if anyone can recommend a reasonably priced 74 series IC testing device I'd be interested - I have quite a few IC's to remove, test and replace.

Thanks

 

[zippysticks]

Hmm, I might already be on to something. The 74LS161 counters at D11-14 that form part of the vide generation timing are a bit suspect. There are four of them in a chain and simply swapping them over is giving quite different results.

 

[Eudimorphodon]

Interestingly, this machine came with a Videx videoterm 80 column card that when installed in this machine and its output switched on (in slot 3) using PR#3 , the 80 column picture view is superb.
I'm not quite sure how much of the onboard video circuitry is replaced by this card to narrow down my fault finding. I suppose its possible its a RAM issue too of course, but difficult to run the RAM test disk with this screen corruption.

The Videoterm 80 generates video completely independently of the main board; you can hook a separate monitor up to it and run your Apple II in a dual-head configuration if you get rid of that little magic switch board that separately plugs into the Apple II's motherboard via a piggyback socket. per the manual that board just does some black magic by monitoring that socket to determine if the Apple is trying to display a graphics mode or not; graphics override the 80 column mode.

So in short the 80 column mode working is completely independent of what's going on with the native video. You might even want to consider removing the VideoTerm board and its piggyback switcher (don't forget to transfer the chip that was removed for it back into its socket) to remove them from the equation.

Hmm, I might already be on to something. The 74LS161 counters at D11-14 that form part of the vide generation timing are a bit suspect. There are four of them in a chain and simply swapping them over is giving quite different results.

It does look very much from your original pictures that the vertical counter chain is incrementing by 2 lines for every one; you're essentially getting two copies of the screen with with half the lines missing from both copies in each frame.

 

[zippysticks]

So in short the 80 column mode working is completely independent of what's going on with the native video. You might even want to consider removing the VideoTerm board and its piggyback switcher (don't forget to transfer the chip that was removed for it back into its socket) to remove them from the equation.

It did not come with the piggyback switcher, just an RCA fly lead to connect the monitor. When you say 'chip that was removed' - what do you mean ? I got this machine with the Videx card and a PAL colour card (also with a fly lead) but no 'chip'

I'm sure the problem is with the 74LS161 counters so Im waiting for some to arrive.

Thanks

 

[Eudimorphodon]

It did not come with the piggyback switcher, just an RCA fly lead to connect the monitor. When you say 'chip that was removed' - what do you mean ? I got this machine with the Videx card and a PAL colour card (also with a fly lead) but no 'chip

Oh, I was assuming from your original post that you were switching between native video and the Videx on the same monitor. Disregard, then.

(If you look in the manual for the card there was an optional autoswitch accessory that included a little piggyback board that plugged into the motherboard… near the upper right-hand corner of the board, if I recall correctly. You installed it by pulling a chip out and transferring it to a socket on the board, that’s what I was referring to.)

 

[Hugo Holden]

Just a tip on the SN74161 counter.

The high quality versions of it were the DM9316. These always came in the ceramic package, very much like what a mil spec 54161 would be.

They still crop up on ebay from very good sellers like Dave & Jan:

9316 F9316 Fairchild IC Binary Counter Ceramic - NOS Qty 1 | eBay

Qty 1 9316 F9316 Fairchild IC Binary Counter Ceramic - NOS.

www.ebay.com

Though , if you wanted to go quality mil spec crazy, you could get the mil spec SN54161J

SN54161J Original Texas Inst. Integrated Circuit | eBay

SN54161J Integrated Circuit. (Specifications: Binary Counter, Synchronous, Up Direction, TTL, CDIP16). Dalbani is a national and international distributor of high quality electronic components and parts.

www.ebay.com

I'm still hunting around for the radiation hardened versions.

 

[zippysticks]

So I have actually managed to get a bunch of mil spec SNJ54LS161AJ ceramic versions and they work perfectly. Machine now sorted with a great video output.