Apple IIe enhanced Clone characters display wrong?

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Apple IIe enhanced Clone characters display wrong?

hi all im hoping to get some help in fixing our iie enhanced clone which displays wrong characters and has a background of apostrophes . It displays: Appde eee (on top) which should be Apple //e? also the ] is displayed as U? keyboard also seems to be delayed/hesitant?

 

the board beeps and boots fine and passes on board diagnostics? all psu voltage rails correct.

 

Ive done some research online and checked usual stuff like video rom/keyboard decoder 3600-pro etc and swapped out the cpu with known working but no change. 

Was going to try swap out the IOU and MMU but the clone uses the STK ASIC chips i remember reading they are not pin compatible can anyone confirm?

 

So far this is what ive tried/tested:

ram - passed with onboard diagnostics (the display however is not the normal but rather checkered but it displays (in wrong characters) system ok

 

swapped out all system roms with known working roms - same screen

 

tried different keyboard, no change

logic board is clean, no traces are damaged

 

my thoughts are a faulty ttl logic chip? anyone know which one to check thats related to the video rom/decoder?

 

will update with photos of the screen im getting once i reconnect everything 

 

thanks in advance:-)

CVT
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Let's look at the binary of

Let's look at the ASCII values in binary, shall we:

 

   ] vs U:

   01011101 (])

   01010101 (U)

 

   / vs e:

   00101111 (/)

   01100101 (e)

 

   l vs d:

   01101100 (l)

   01100100 (d)

 

   space vs backwards apostrophe:

   00100000 (space)

   01100000 (`)

 

As you can see the second bit (counting from left to right) is stick at 1, while the fifth and the seventh bits are stuck at 0.

 

I would start with the character ROM.

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Hi CVT, thanks for responding

Hi CVT, thanks for responding, forgot to mention i tested the keyboard and video roms and both were working on another 2e and vice versa. The only IC's left that haven't been swapped so fare are the IOU/MMU im leaning towards the IOU as a possible issue but the clone uses STK 65371 , i can swap out with the apple iie IOU but not sure if they are the same/ or possibly damaging the original IOU?

 

Re the TTL's So far have tried (via piggy back as they are all soldered) 74LS166 and 74LS10 no change

waiting on parts to test the others in the video circuit)

CVT
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First of all you shouldn’t

First and foremost you shouldn’t piggy back the IOU or the MMU, because you might end up with 2 machines that need those chips, instead of possibly none.

 

From what I can gather the problem is either in the CD-ROM chip, the 74LS374 or 74LS245. Also it would be useful to know if it's a 1:1 Apple IIe clone or not. If not, please provide the make and model. It is definitely not in the video circuit, so don't bother looking there.

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the MMU and IOU are both

the MMU and IOU are both socketed on the clone so would be an easy switch I just cant get any info online if anyone has tried to replace these and if working? Ive only tried the TTL 74ls chips via piggy-back method as they are all soldered on the clone.

 

no name on the board but it looks identical to the iie , uses the same roms, just not sure if the real MMU/IOU will work on the clone - if anyone has done it/can confirm either way that would be great..

 

All the roms on the clone ive tested and used them on the real iie which works perfectly with them . Ive checked the roms all are exact copies of the iie.

I will try the 374 and 245 and report back

 

 

 

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I used to have a couple of

I used to have a couple of IIe clones. I tried swapping the MMU and IOU with a regular IIe and they were completely compatible. Of course there’s always the possibility that yours is different

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STK

Was the exchange successful? I could help you

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