Novice Apple 2e user needs help

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Novice Apple 2e user needs help

Hi folks,

  I have a situation here I need help with.  Quick background: I recently recovered my childhood Apple 2e Enhanced from my parents and it worked - I was thrilled, discovered a thriving Apple II enthusiast community and a bunch of innovative people making cool devices for the vintage computers.

My setup:

Apple IIe Enhanced 128k 607-187 Motherboard

Aux slot - 80 column card

slot 3 - Uthernet II (a2RetroSysyems.com)

slot 5 - FastChip //e (a2heaven.com)

slot 6 - Yellowstone Universal Disk card (BigMessOWires.com)

slot 7 - AllVGAS VGA scaler (a2heaven.com)

Also : Power supply from ReactiveMicro.com and his 12 inch color LCD through composite video - so I had 2 monitors connected - 1 through VGA and 1 composite video 

My source for software is the FloppyEMU floppy disk emulator from BigMessOWires.com

Everything was working until yesterday when I went to move some cards around because I was having some odd behavior with the FastChip on boot when it was disabled (I disabled it when not using because it caused some software I had to glitch) - I had to remove jumper wires connected to LS166, IOU and S10 for the VGA scaler and it was difficult getting them off the pins. Now my Apple II only boots to a prompt. It will not access a drive. I've removed everything and kept in only the original Disk II card and 80 column card - tried multiple slots and nothing- straight to a prompt. Built in system test says system ok (ctrl-both apples-reset). PR#6 just hangs. I have no idea what else to try - praying this isn't a nostalgic paper weight now. Any advice would be greatly appreciated. Thanks!

 

 

 

 

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Boot ROM access

Looks like your machine is having trouble with accessing the ROM on the disk II card. C600 is the ROM of the disk II card - assuming you have inserted it in slot #6 (where it normally is). Your dump is showing bad/random data - no wonder the CPU is crashing (since it's hitting a BRK instruction).

 

This is how the disk II card's ROM at C600 should normally look like:

 

So, it could be an issue with the ROM or interface card itself. Or it could be an issue with the mainboard logic - so it's unable to access the ROM of any card. What happens if you remove the disk II card - and plug another card with a boot ROM instead - like the Yellowstone card. Try this - and maybe show a photo of how the dump looks if it also crashes.

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Apple IIe problem cont.
Here is with the Yellowstone in slot 6 - same results in slot 5 

 

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Mainboard issue

So, it's not the card - but the mainboard. The machine is unable to access the ROMs on any card.

What happens when you type "C600L" repeatedly. Does the content of the ROM dump change (some bits change), or does it always look exactly the same? Also, try dumping the (non-existent) ROM of any unused slot - like C400L (when no card is in slot 4). How does the dump look then? These memory dumps can sometimes give a clue at what exactly is failing...

Since the machine is otherwise working, and only slot access isn't working, I would suspect an issue with one of the chips driving the slot signals. The Apple IIe has chips to separate the signals from the slots from those on the mainboard. A frequent suspect is the driver for the data bus (LS245 at UB1). It's not uncommon for this IC to fail. Otherwise, since ROM access at CnXX isn't working, the address decoder LS138 (at UB4) would also be a likely suspect (so, with a "shotgun approach" you could just try replacing both - they are cheap and still super-common. And they are both socketed, since, well, they are both driving the slots, so more easily damaged...).

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Apple IIe problem cont.
Here's is C400L with no card in slot. Where would I buy said chips? I looked on eBay and didn't see anything. Wow I pulled out LS138 trying to see if I could reseat it and it bent all to Hell coming out and went flying - ugh. Is there a trick to removing safely - now I definitely need that one - and to put them in safely?

 

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m0ebiu5 wrote:[[{"fid":"35939
m0ebiu5 wrote:

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You can find 74LS138 and 74LS245 on eBay or even Amazon.  Unfortunately most of the big electronics suppliers like Mouser or Digi-Key don't seem to reliably stock 74LS parts anymore.

 

If it is the PROM, then you are basically SOL as they are hard to find.  In most cases these days it is easier to just buy another controller card than to find a P5 or P6 PROM or a blank 6309 type BiPolar PROM (and then even if you have a blank, it is hard to find anyone who can program one since most modern programmers don't do those old chips anymore).

 

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Sometimes the dumps are very

Sometimes the dumps are very telling when only specific bits are affected. I don't see any pattern with these dumps, however. So not conclusive.

The chips are easy to obtain. You will find then both on ebay, as well as from any respectable electronic parts distributor. Make sure to search with the full part number: "74LS245" and "74LS138" (or "SN74LS245", ...).

Here's another idea: you mentioned an 80 column card in your aux slot. Remove this card - and have a look: it should also have a 74LS245 - and it's usually also socketed. You could borrow this IC - and use it to replace the UB1/LS245 on the mainboard. Then test your machine again (without the AUX card). If the machine works and boots from disk again, you know it's indeed the LS245. Otherwise, it's got to be something else. If you had more cards for the Apple II, you might be lucky and also find one where you could temporarily borrow the 74LS138. It's also present on many cards.

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Apple IIe problem cont.

One other question - do you think the pins that I connected the jumpers from the VGA card to have nothing to do with it? Trying to wiggle those jumper clamps off wasn't easy - connected to LS166, IOU, S10.  I didn't go anywhere near the LS245 or the LS138 though it's above the S10.  Thank you both for your help - I will buy these 2 chips and pray that they solve the issue.

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Other causes for failures

The 74LS245 would usually just fail with age - mostly has nothing to do with touching.

But, ok, I'm not familiar with the VGA scaler and the wiring/clamps you mention. Maybe show a photo of what was connected before and what you had to remove (or maybe someone else on the forum is familiar with it).

Indeed, if the machine stopped working exactly after you've been working on it, then other reasons for the machine to fail are also quite possible (indeed maybe even more likely than an ageing IC, failing at exactly the moment that you had the case opened).

Especially if you had to apply force and wiggled the mainboard, it could be cracked solder joints or broken traces. Or bad IC contacts - especially if you removed something which was "clamped" to the ICs before. In that case a close visual inspection may help. Also, remove and reseat socketed ICs - especially in the area where you had clamps. If there were broken traces/solder joints, it sometimes helps to carefully apply a bit of pressure in different areas of the mainboard, while switching the machine on. That can help to identify the presence of a bad contact.

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I see...

I see...

In that case, closely inspect these ICs. Pin 3 of the LS10 at UC5 has a bitstream of video signal - which is why the VGA scaler connected to it. But some of UC5's gates are indeed involved in addressing the I/O slots - especially pins 1+2, which are directly next to where the red clamp was. So, yes, if these pins got bent, this could affect the slots...

Start with removing the LS10 at UC5. Make sure its pins are not bent and it makes proper contact with the socket. If that doesn't help, do the same with the IOU. The LS166 at UF5 is not socketed - so you can just visually inspect the solder contacts (make sure nothing is wedged between the pins or broken).

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Apple IIe problem cont.

The red I really had trouble with multiple times that removed it. My concern would be damaging them trying to take the IC off - I really mangled LS138 taking it off.

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Apple IIe problem cont.

Do the IC pins need to flex outward to make contact or inward?

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Did you remove the clamps -

Did you remove the clamps - or temporarily remove and reinstall them? The photo above looks a bit like the red clamp was wedged in between pin 2 and 3. If the clamp bridged those pins, then yes, the slots certainly would not work (it would affect an upper address line, which is connected to the I/O strobe signal for the slots).

The 74LS10 is another cheap, standard device. These clamps are also nothing special. If the machine isn't working anyway, I wouldn't worry about removing any of those. They are all easily replaced.

 

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Apple IIe problem cont.

They are currently off and directly after I took them off Saturday morning and moved a few cards this happened.  

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If you don't have the special

If you don't have the special tool that allows you to pull the chips straight up, you can use two small screwdrivers as levers to lift both sides simultaneously. If you only have one or space doesn’t allow it, you can do one side at a time, but lift just a bit and go to the other side. Keep switching sides and try to keep the chip leveled as it does up.

 

Once the chip is out, you can use the same approach to also remove the plastic part of the socket in order to expose the contacts and to make sure nothing is mangled or jammed.

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Apple IIe problem cont.

What are the names of the chips I need to replace for the IOU and S10 If they are damaged - what to look up on eBay?

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I don't think the 74LS10 was

I don't think the 74LS10 was damaged. Both immediate neighbours of pin 3 are also inputs, so a short between pins 2 and 3 or 3 and 4 caused by pulling the red clamp sideways would not damage this chip.

 

Hopefully it's not the IOU, since it's almost impossible to find.

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Apple IIe fixed!
Thank you all for your help - it was indeed the 74LS245 IC that was the culprit - I'm back in business - I can't thank you all enough.

 

 

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I'm starting to think the 245

I'm starting to think the 245 fails more than other chips including the Apple MT RAM.  Not sure why they are so sensitive, other than they are first in line. Although I killed one inserting a card with the wrong end facing the keyboard, I gotta remember to add a "facing keyboard" label so I don't make random mistakes thinking I know what I'm doing with the tiny cards.

 

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Great news

Great news. Always good to see a machine revived! (And forum members which report back when it has worked...)

Yes, the LS245 is a fairly common culprit. It does fail more often than other ICs of the LS TTL series - which is why Apple placed it in a socket. Reason is probably obvious once you compare data sheets. The LS245 is a bus driver. It's able to sink a current of 24mA per output - and it has 8 of them. That's quite a bit of power - so it does get warm in normal operation. It's having a relatively tough live constantly driving the data bus signals...

If you compare this to other basic LS TTL logic gates (like the 74LS00 etc): these usually only drive 4-8mA per output - and most of them only have 2-4 outputs. Most LS TTL ICs consume less power in total, than the LS245 is able to drive on a single pin... So, yeah, I think it's got a pretty good excuse for often being among the first to quit.

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One approach is to replace it

One approach is to replace it with the 74HCT245, which runs much cooler.

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CVT wrote:One approach is to
CVT wrote:

One approach is to replace it with the 74HCT245, which runs much cooler.

Is using the HCT series to replace LS chips generally safe in Apples if an equivalent exists? Or are there some cases where you would want to stick with LS?

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nick3092 wrote:CVT wrote:One
nick3092 wrote:
CVT wrote:

One approach is to replace it with the 74HCT245, which runs much cooler.

Is using the HCT series to replace LS chips generally safe in Apples if an equivalent exists? Or are there some cases where you would want to stick with LS?

 

"Generally", may be too optimistic.  A lot of the time it will work, maybe even most, but certainly not all.

 

74HCT245 will usually work as a replacement in a lot of places where a 74LS245 was originally used, but by no means all.

Other 74HCT and 74LS chips may be more or less likely to be interchagable.

They are mostly signal level compatible but things that are dependent on specific timing or load behavior may not work.

 

So it is basically something you have to try and then test thoroughly.  Because often substitutions like this will seem to work fine until edge cases come into play and then failures may be interesting.

 

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That is true, the 74HCT

That is true, the 74HCT series are more than twice faster than the 74LS series and in certain cases they can produce undesired results. One example is using logical gates in order to produce a delay: the resulting delay will be shorter with 74HCT.

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CVT wrote:That is true, the
CVT wrote:

That is true, the 74HCT series are more than twice faster than the 74LS series and in certain cases they can produce undesired results. One example is using logical gates in order to produce a delay: the resulting delay will be shorter with 74HCT.

 

This is exactly the kind of thing I'm talking about.  It may not even be delays that are intentional that get messed up.  If you replace a 74LS with a 74HCT in one part of a circuit but another dependent part is left all 74LS, the side with the HCT may be out of sync with the other side.  It is for cases like this tthat I say you have to test carefully when you make substitutions because there may be unknown side effects.  You can't just assume it will work or only do a very simple cursory test and be confident that it will work in varied operation.

 

 

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For synchronization issues

For synchronization issues caused by a faster propagation delay we need to look at the frequency of the circuit. If the speed of the 74LS series is ~30 ns and the speed of the 74HCT series is ~12 ns, then being ~20 ns faster equates to 50 MHz. Even if we divide it by 4 for good measure, the only thing in the Apple II that runs anywhere near this frequency is the composite signal generation circuitry.

 

The other thing is that a lot of new chips that are labeled 74LS are actually 74HCT and no one notices. There are even cases when they are 74HC and that can be a real problem as shown in a few videos on YouTube. My TJ Boldt ProDOS card came with 3 of these so-called “74LS245”. (I got suspicious when I noticed that they don’t heat up at all.) So I decided to measure their temperature in my Apple IIe after it has been running for a while with the slots full of old TTL cards:

 

Original 74LS245 chip from 1983: 36°C

TI 74HCT245N from a reputable source: 28°C

These so-called "74LS245N": 21°C (This temperature makes sense if it's actually 74HC245.)

 

Ambient temperature: 18°C

 

They don’t cause any issues and so far I haven't found a test that I can run on the Apple IIe that can detect them, but I am open to suggestions.

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