SINGLE TOOTH Posted March 7, 2018 Share Posted March 7, 2018 So I got a C64 a while back at goodwill for $2.99. It's an early board, version 326298. It hasn't worked since I bought it. When you plug it in, just a black screen. If you put a cartridge in, there's a garbled screen. Some people on a Commodore group thought it might be the PLA, so I bought a PLAnkton chip and installed it. No change. I then decided to start removing RAM chips and putting sockets in them. Anyone know a good source for these chips? Anyway, while removing the chips I managed to destroy the glass (didn't know those existed) capacitor at location C43. The schematic shows it's value as .22. The label on the capacitor is labeled "224." See attachments. A couple of questions: 1. Anyone know a possible cause of the garbage screen? 2. I'm not too savvy with the different RAM chips, anyone know a source for these? 3. And now I need a source for the glass capacitor at C43. What kind of capacitor/value can I use as a replacement? Quote Link to comment Share on other sites More sharing options...
carlsson Posted March 7, 2018 Share Posted March 7, 2018 I think any 4164 DRAM would work. I don't remember the minmum speed, but here is for instance a 150 ns one at Jameco: https://www.jameco.com/z/4164-150-Major-Brands-64KX1-DIP-16-DRAM-150NS_41662.html Also I don't know if the glass capacitor has any particular properties over a 0.22 uF ceramic capacitor. Someone will want to chime in on this, but you should easily be able to find compatible types of non-polarized capacitors, though with an early board you probably want glass to match the broken one. Strange that replacing the PLA didn't solve your issue. I suppose the VIC-II chip could emit problems too. If the character ROM was at fault, a game cartridge that uses custom graphics most of the way would bypass the ROM. Something about memory decoding that is outside of what the PLA does? Quote Link to comment Share on other sites More sharing options...
White Flame Posted March 8, 2018 Share Posted March 8, 2018 Is the garbage static or does it flicker around? Quote Link to comment Share on other sites More sharing options...
SINGLE TOOTH Posted March 8, 2018 Author Share Posted March 8, 2018 Is the garbage static or does it flicker around? Pretty much static until you power cycle. Quote Link to comment Share on other sites More sharing options...
+OLD CS1 Posted March 8, 2018 Share Posted March 8, 2018 One of the CIAs is also responsible for setting the bank of 16k memory the VIC-II uses. Quote Link to comment Share on other sites More sharing options...
shoestring Posted March 9, 2018 Share Posted March 9, 2018 (edited) It wouldn't be the character rom if it's booting to junk like that. You should still be able to load programs and the machine should still function in this case. Things it could be * Bad ram, try replacing/swapping U12 first. * Bad multiplexer at U14 ( common fault if it's a MOS chip ). * Faulty U2 - CIA, swap them around ( they're identical ) to see if your symptoms change. Edited March 9, 2018 by shoestring Quote Link to comment Share on other sites More sharing options...
SINGLE TOOTH Posted March 14, 2018 Author Share Posted March 14, 2018 I made some progress, the cart boots now. I swapped all the ram. Basic does not boot yet. I tried swapping u13 but no luck. 2 Quote Link to comment Share on other sites More sharing options...
shoestring Posted March 14, 2018 Share Posted March 14, 2018 What happens when you try and boot basic ? See if the below symptoms match yours. U3 901226-01 BASIC ROMBlank screen w/ border. Cartridge works.U4 901227-03 (early -02) KERNAL ROMBlank screen, no border. Cartridge works ftp://www.zimmers.net/pub/cbm/documents/repair/troubleshooting-c64.txt. Quote Link to comment Share on other sites More sharing options...
SINGLE TOOTH Posted March 14, 2018 Author Share Posted March 14, 2018 What happens when you try and boot basic ? See if the below symptoms match yours. U3 901226-01 BASIC ROM Blank screen w/ border. Cartridge works. U4 901227-03 (early -02) KERNAL ROM Blank screen, no border. Cartridge works ftp://www.zimmers.net/pub/cbm/documents/repair/troubleshooting-c64.txt. I still just get a pure black screen without a cartridge inserted. I'll check the link. Quote Link to comment Share on other sites More sharing options...
Zippy Zapp Posted March 14, 2018 Share Posted March 14, 2018 (edited) Sure sounds like a Kernal (U4) or BASIC (U3) ROM problem. Have you tried replacements? http://personalpages.tds.net/~rcarlsen/cbm/c64/c64-ic.txt Edited March 14, 2018 by Zippy Zapp Quote Link to comment Share on other sites More sharing options...
SINGLE TOOTH Posted March 14, 2018 Author Share Posted March 14, 2018 Sure sounds like a Kernal (U4) or BASIC (U3) ROM problem. Have you tried replacements? http://personalpages.tds.net/~rcarlsen/cbm/c64/c64-ic.txt I have not, I have no replacements. I basically have no Commodore chips to swap. Quote Link to comment Share on other sites More sharing options...
shoestring Posted March 14, 2018 Share Posted March 14, 2018 I wouldn't replace it with an original pull, those 3 mask roms ( kernal, char rom & basic rom ) are prone to failure. You can replace those chips using a standard 27c64 EPROM if you have the tools or know someone who can do it. I did something similar to replace the character rom. Check this out http://ezcontents.org/c64-basic-rom-27c64-eprom Quote Link to comment Share on other sites More sharing options...
SINGLE TOOTH Posted March 14, 2018 Author Share Posted March 14, 2018 Sadly I dont have a programmer Man, what chip isnt prone to failure on these things?? Quote Link to comment Share on other sites More sharing options...
shoestring Posted March 15, 2018 Share Posted March 15, 2018 (edited) Still not too bad after 35 years when you think about it You could try your chances on eBay. https://www.ebay.com.au/sch/i.html?_odkw=c64+basic+rom&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.X901226-01.TRS0&_nkw=901226-01&_sacat=0 Edited March 15, 2018 by shoestring Quote Link to comment Share on other sites More sharing options...
SINGLE TOOTH Posted March 18, 2018 Author Share Posted March 18, 2018 I found a voltage regulator was super hot even when only powered on a minute or two and actually was burning the board. I wonder if that's causing some of the issues. Anyone know a suitable replacement? It's labeled UA7805UC. Quote Link to comment Share on other sites More sharing options...
carlsson Posted March 18, 2018 Share Posted March 18, 2018 No idea how hot it should be, but it looks like a standard 7805 voltage regulator to me. If it is made by Fairchild Semiconductors, UC seems to refer to the TO220 packaging and their 7805's were specified to operating at 0 - 125 C, soldering at 230 C for max 10 seconds. I would think any 7805 in the same package would work. Nowadays people are talking about more efficient switching voltage regulators, but I don't know if those are feasible here or perhaps more expensive for the task. 1 Quote Link to comment Share on other sites More sharing options...
SINGLE TOOTH Posted March 18, 2018 Author Share Posted March 18, 2018 No idea how hot it should be, but it looks like a standard 7805 voltage regulator to me. If it is made by Fairchild Semiconductors, UC seems to refer to the TO220 packaging and their 7805's were specified to operating at 0 - 125 C, soldering at 230 C for max 10 seconds. I would think any 7805 in the same package would work. Nowadays people are talking about more efficient switching voltage regulators, but I don't know if those are feasible here or perhaps more expensive for the task. Thanks, I'm not so good at breaking down the codes on these packages. I ordered some 7805's to replace with. I don't think it should have been this hot. You can see it was even browning the board. Quote Link to comment Share on other sites More sharing options...
shoestring Posted March 18, 2018 Share Posted March 18, 2018 It's quite normal for these to get hot to the touch, especially without a heatsink. This should also work https://www.mouser.com/ProductDetail/Murata-Power-Solutions/OKI-78SR-5-15-W36-C/?qs=uJpRT2lXVNXJP%252bo08dQqJQ== Data sheet here https://www.mouser.com/ds/2/281/oki-78sr-56393.pdf "are a direct plug-in replacement for TO-220 package 78xx series linear regulators." 1 Quote Link to comment Share on other sites More sharing options...
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