Project: Apple IIc video/boot problem

[theslownorris]

SO I have a new project IIc.

When I power it up I get no disk drive spin, just power and vertical color bars.

After disassembling it I found an anomaly at the location of the character ROM socket.

The socket is a 28-pin.

The chip in it is 24-pin, labeled 342-0265-A, and if i move it around slightly it get variations in the video output.

I believe this chip may be a video ROM chip for a IIe enhancement kit? (No real knowledge here, just a google search).

Is this the correct chip for the IIc?

Any help would be great.

Thx

 

[Gorgonops]

It's the character generator ROM, and the same chip is used for IIe's and IIcs. (The reason this ROM was swapped out when upgrading an original IIe to an "Enhanced" IIe was to add MouseText characters.)

 

[theslownorris]

Great! I have a spare platinum IIe motherboard. I'll try for the swap, dunno why I didn't think of it??? ????

 

[theslownorris]

Well, back to the drawing board. I swapped in a known good Character ROM and even a known good 65C02 (Both from a Platinum IIe)...

Netted same results... 

Prob, just let it slide away... got too many projects now.

 

[bhtooefr]

If you're getting no disk drive spin, no beep, the problem isn't in the character generation circuit.

Your CPU most likely isn't starting up, so suspect a failed keyboard (holding Ctrl-Reset, or having the keyboard unplugged, can cause those symptoms IIRC), failed CPU, failed ROM, or failed first bank of RAM (IIRC in that order). Could also be the IOU or MMU, but that's getting lower in likelihood IIRC.