+bf2k+ Posted November 13, 2021 Share Posted November 13, 2021 Is this wire soldered to pin 16 of the MMU? Quote Link to comment Share on other sites More sharing options...
Gunstar Posted November 13, 2021 Share Posted November 13, 2021 (edited) That wire pictured is connected to pin 5 of the MMU. Edited November 13, 2021 by Gunstar Quote Link to comment Share on other sites More sharing options...
Rybags Posted November 14, 2021 Share Posted November 14, 2021 That's tapping into A15, so potentially could be part of numerous aftermarket addons. Or might just be a patch lead due to a severed trace elsewhere. Quote Link to comment Share on other sites More sharing options...
Calibus Posted November 14, 2021 Share Posted November 14, 2021 7 hours ago, bf2k+ said: Is this wire soldered to pin 16 of the MMU? I'm guessing you are counting starting from the wrong side of the notch. The pins are numbered counter clockwise. If they were numbered clockwise (starting to the right of the notch, instead of the left) then indeed - that would have been pin 16. Since the pins are numbered counter clockwise, pin 1 is to the left of the notch, so the wire is on pin 5. 1 Quote Link to comment Share on other sites More sharing options...
+bf2k+ Posted November 14, 2021 Author Share Posted November 14, 2021 Yes I was counting in the wrong direction because in this particular 600XL half of the 40 pin chips had a white dot on pin 40 and the other half of the chips had the same dot on pin 1 - very confusing when you don't do this every day. I did manage to figure out my mistake before applying power and the machine is working great now. I had to rob a PIA from another machine. Does anyone sell PIAs... I guess that is a 6520-A? Is a 6520-P equivalent or not? Quote Link to comment Share on other sites More sharing options...
55five66six Posted November 14, 2021 Share Posted November 14, 2021 1 hour ago, bf2k+ said: Yes I was counting in the wrong direction because in this particular 600XL half of the 40 pin chips had a white dot on pin 40 and the other half of the chips had the same dot on pin 1 - very confusing when you don't do this every day. I did manage to figure out my mistake before applying power and the machine is working great now. I had to rob a PIA from another machine. Does anyone sell PIAs... I guess that is a 6520-A? Is a 6520-P equivalent or not? https://www.best-electronics-ca.com/custom-i.htm That's the only place I could think of.. Hopefully it helps. Quote Link to comment Share on other sites More sharing options...
1050 Posted November 15, 2021 Share Posted November 15, 2021 (edited) https://www.jameco.com/z/68B21-Major-Brands-IC-68B21-PERIPHERAL-INTERFACE-ADAPTER-8-BIT-2MHz-DIP-40-pin_43414.html This is an equivalent and suitable for direct replacement for our 6520 PIA. eBay might be loaded with fake offerings which is on the rise over there, so very glad I purchased full tubes of these and others before scammers had a reason to exist in that trade. A is purportedly a 1 MHz design and not good enough for our 1.79 MHz clock. B is purportedly for 2 MHz and is supposed to work, but I won't stand behind it. I'll stand behind it when they SAY it's 2 MHz and only then like when Jameco says it. And I trust they are NOT selling fake chips too. P usually stands for Plastic (instead of ceramic) case so who knows given there are at least two flavors available? Edited November 15, 2021 by 1050 further info added Quote Link to comment Share on other sites More sharing options...
manterola Posted November 15, 2021 Share Posted November 15, 2021 Motorola PIA the 2MHz variant is also compatible. I use it all the time. Not sure if the link posted by @1050 is or isn't Motorola... Anyway, PIAs are easy to source compared with other Atari 8 bits chips. Quote Link to comment Share on other sites More sharing options...
Mathy Posted November 16, 2021 Share Posted November 16, 2021 Hello guys Beware, the letters used to distinguish between different speed versions of the 6521 and the 6820 don't denote the same frequencies! Sincerely Mathy Quote Link to comment Share on other sites More sharing options...
+bf2k+ Posted November 16, 2021 Author Share Posted November 16, 2021 I ordered a couple of Motorolas from Jameco. Thanks for the input !! 1 Quote Link to comment Share on other sites More sharing options...
kenames99 Posted November 17, 2021 Share Posted November 17, 2021 you could also use the 6521 available from Western Design Center (WDC) available from most resellers like mouser or digikey. Ken Quote Link to comment Share on other sites More sharing options...
+bf2k+ Posted November 19, 2021 Author Share Posted November 19, 2021 So I got this one but it didn't work... Quote Link to comment Share on other sites More sharing options...
ClausB Posted November 19, 2021 Share Posted November 19, 2021 No, the MC146823 is not compatible. It has 3 ports, where PIA has 2. Did the seller claim compatibility? Quote Link to comment Share on other sites More sharing options...
_The Doctor__ Posted November 19, 2021 Share Posted November 19, 2021 (edited) mc146823p is not pin compatible and is not a dual port device, it is 3 ports. I think you clicked an incorrect, or suggested link... always compare pin outs https://html.alldatasheet.com/html-pdf/111928/MOTOROLA/MC146823P/386/1/MC146823P.html vs https://www.westerndesigncenter.com/wdc/w65c21-chip.php https://wdc65xx.com/65xx-chips/w65c21-peripheral-interface-adapter-pia/ and of course you can see the 6520 the same way here's a cross reference sheet http://westerndesigncenter.com/wdc/documentation/WDC65xxCrossPartslist2017.xlsx Edited November 19, 2021 by _The Doctor__ Quote Link to comment Share on other sites More sharing options...
+bf2k+ Posted November 20, 2021 Author Share Posted November 20, 2021 I ordered a 65c21 today. Thanks! Quote Link to comment Share on other sites More sharing options...
+bf2k+ Posted November 20, 2021 Author Share Posted November 20, 2021 4 hours ago, ClausB said: No, the MC146823 is not compatible. It has 3 ports, where PIA has 2. Did the seller claim compatibility? No. It was probably my mistake. Quote Link to comment Share on other sites More sharing options...
BillC Posted November 20, 2021 Share Posted November 20, 2021 3 hours ago, bf2k+ said: No. It was probably my mistake. One problem is that when you search for specific parts search engines often include similar parts, you have to be careful what you select from the results. Quote Link to comment Share on other sites More sharing options...
+bf2k+ Posted November 20, 2021 Author Share Posted November 20, 2021 5 hours ago, BillC said: One problem is that when you search for specific parts search engines often include similar parts, you have to be careful what you select from the results. I think that is exactly what happened... Quote Link to comment Share on other sites More sharing options...
Mclaneinc Posted November 20, 2021 Share Posted November 20, 2021 10 minutes ago, bf2k+ said: I think that is exactly what happened... Yup, so easy with the searches these days, I normally put quote marks around the actual part number so it's more direct for the quoted part. And like the others have said, it's always counterclockwise from the notch in the DIL chip. Very easy mistake to make., hope the new part works.. Paul.. Quote Link to comment Share on other sites More sharing options...
+bf2k+ Posted November 20, 2021 Author Share Posted November 20, 2021 This time I ordered two different ones... Quote Link to comment Share on other sites More sharing options...
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