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Apple IIe not booting

G

GrahamN

Member
Joined
Feb 5, 2015
Messages
19
Location
Burnham on Crouch, UK
Can anyone give me some advice on a problematic Apple IIe?

This is a UK spec. PAL version, that was in very poor condition when I got it (damp mainly), and I have been slowly refurbishing it.

I've replaced the capacitors in the power supply, and the RAM chips looked rusty on their legs so I've replaced them (I used 4864P-3 which seemd to be equivalents of the MCM6665BP20 that were originally fitted except slightly slower which I've assumed is not critical), but when I switch on I get horizontal lines on rhe screen and no beep from the speaker.

I've tried a replacement 65C02 and there is no difference. The reset circuitry seems to be OK (Pin 40 on the CPU goes low when control and reset are pressed), and the clock also seems OK.

I don't have any replacement Apple specific chips to try swapping, but I've tested all the socketed TTL and they are fine.

Can anyone suggest what my next step should be? Or have I made an incorrect assumption regarding the RAM and the Apple is fussy about the right chips?

Any suggestions would be appreciated.

Thanks

IMG_2915-1600.jpg

IMG_2916-1600.jpg
 
I've tried to locate the exact data sheets that match the DRAMS you have used - but couldn't find what I was looking for with the MCM6665BP20.

They both claim to be 200 ns access time devices (from /RAS to data available) but there are a couple of other parameters that are important:

1. Cycle time (rom /RAS to the next /RAS). This is identified as 335ns for the 4864P-3. I can't find this parameter for the Motorola RAM.
2. Refresh cycles. Most early devices are 128 cycle/refresh - but later ones came in 256 cycles/refresh. You can't put a 256 in place of a 128 (but you can do the opposite).

To be safe, I would try and locate some DRAMS that are faster than 200 ns with 128 cycles/refresh.

EDIT: Just checked what I used to repair a duff DRAM chip in my Apple IIe - Texas Instruments TMS4164-25. These are rated at 250 ns access time - so I doubt whether your replacement devices account for your problem.

Your video image is interesting though... Let me think on that one.

Dave
 
Thanks

I have located some RAM of the right type, but it's pretty expensive, so I would prefer not to get it if I didn't need to - on the other hand, if it is likely to be a RAM problem, then I do have that as an option. I should have said that I have checked and there is activity on all RAM data pins.
 
If your RAM pins were rusty, there may be corrosion on nearby traces. I would check all the data and address lines for continuity and shorts.
 
The board itself has no obvious corrosion - and I've checked for shorts on the data and address lines. The data lines are certainly OK with ref to continuity, but I have't checked the address lines as yet.
 
Okay - I'm now completely confused! I've been looking through some old PCBs, and found a ZX Spectrum with 4164 200ns RAM chips in working order. So, I replaced the Apple RAM with these and instead of horizontal lines I got vertical lines! As far as I can see these are exact replacements chips.

IMG_2917-1600.jpg
 
Okay - I've just tried reading the ROMS in my programmer (set as 2764), and one shows just FF al the way through, the other isn't recognised at all. The next step is possibly to burn new eproms and see what happens...
 
Just to update this thread. I ended up having to burn new 4 new EPROMs after which I had a working board. I also had to replace the keyboard encoder chip in order to get the keyboard working properly. I still have about 12 keys that don't work, so will strip down and refurbish them over the next week or so. Other than that, though, I now have a working IIe enhanced. :)
 
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