68kMLA Classic Interface
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| Macintosh 128k Video Problem | |
| Posted by: MacAttack on 2018-03-04 17:48:00 Hello, I recently bought a 128k Mac (non-functioning) and the seller told me that he thought that the 74F253 Ram Multiplexers were bad. But after replacing them with new Motorola ones, the screen still has the same issue. Here is a photo:  I have no idea where to got from this point and a google search came up inconclusive. Please Help!! | |
| Posted by: MacAttack on 2018-03-04 17:48:55 Also the boot sound is gargled, forgot to mention that 😛 | |
| Posted by: techknight on 2018-03-04 17:56:24 do you have a 512k or a plus or the like you could swap ROMs around? | |
| Posted by: MacAttack on 2018-03-04 17:57:12 Yeah, a plus and I’ll try that. | |
| Posted by: MacAttack on 2018-03-04 18:10:52 I tried but it gave me the same screen. :-/ | |
| Posted by: unity on 2018-03-04 18:48:04 Did you swap just the ROMS or the entire board. I would have swapped the board, a lot easier and would rule out bad RAM. | |
| Posted by: MacAttack on 2018-03-04 18:52:54 The ram has been socketed and replaced so I ruled that out and the Mac plus board is not compatible with the 128k case | |
| Posted by: unity on 2018-03-04 19:40:16 You yourself socketed and replace the RAM? Does not matter about board fit, its compatible for testing. You dont have to put the rear bucket on. | |
| Posted by: MacAttack on 2018-03-04 21:42:24 No, not myself so I guess it could be bad ram, but I'm just going off what the seller said. Anyways, I will test the Mac Plus board in it too. | |
| Posted by: techknight on 2018-03-05 15:47:31 If the ROM is good, and the RAM is good, then one of the GALs/PALs could be at fault. OR there is the rare possibility that this mac had a memory upgrade and someone removed it trying to get it original but didnt undo the mods required to the board. | |
| Posted by: MacAttack on 2018-03-09 17:13:45 What chips are the GALs/PALs? | |
Posted by: beachycove on 2018-03-09 20:25:03What chips are the GALs/PALs?I guess there are the best looking and the friendliest. You might want to take one out! | |
Posted by: Jinnai on 2018-03-10 15:51:50I guess there are the best looking and the friendliest. You might want to take one out!Wish I could upvote this post 🙂 But yeah lets get a good picture of the motherboard, I'd say. | |
| Posted by: MacAttack on 2018-03-17 13:08:25 So I want to replace the ram. I thought these chips would work. Any objections? https://www.jameco.com/z/4164-150-Major-Brands-64KX1-DIP-16-DRAM-150NS_41662.html?CID=GOOG&gclid=EAIaIQobChMI4JOMn5T02QIViV5-Ch09NgcCEAQYASABEgJPYfD_BwE | |
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