Phantom drive?
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From: Paul Förster on 6 Nov 2009 12:04 Hi Ruud, On 2009-11-06 13:22:22 +0100, Ruud <Ruud.Baltissen(a)apg.nl> said: > I meant that you have to check if there is a short circuit between > Data and Ground and/or Clock and Ground. Preferably with no 7406 in > the socket. > Just an idea: what you can do is insert CIA2 but leave out all pins > involved with the IEC bus. IMHO in this way the C64 should act as if > there is no drive connected. .... ok, here are my findings: I put CIA2 in a socket and bent pins 5, 6, 7, 8 and 9 one after the other. But I only bent one pin at a time so that all other pins were connected. The result was good when each of the pins 5, 6, 8 and 9 were bent away. Only with pin 7 bent away the symptom remained. To me this means it could be any one of these four pins in combination with pin 7. Still, I can't find no short. :-( I decided to analyze U3 too and found some very strange things indeed: 1. I can't find pins 1, 2 and 3 of U3 anywhere in the schematic. 2. By checking your dead board I found by accident that U3 pin 1 is short with U2 pin 1. I cross checked with my board and they are open. If I short them as with your dead board, I get a high beep sound and no picture. I power off, remove the connection and all is well. Very strange... 3. According to schematics, U3 pin 4 should go to U7 pin 13 and U8 pin 38. While it is connected correctly to U8 pin 38, it is connected to U7 pin 16 instead of 13. This is the same with your board. Are there bugs in the schematics? -- cul8er Paul paul.foerster(a)gmx.net
From: Webster on 6 Nov 2009 13:34 Paul F�rster wrote: > ... oh, this is strange. The C64 wouldn't show a picture without the > 7406 previously. Now it does. Don't aks me why... You made me curious to > give it another shot and so I removed the 7406 again and now the C64 > properly powers on. > > I've cross-checked all combinations, not just neighboring lines of the > serial connector and the 7406 socket each. There are no other shorts > than pin 1 and pin 5 of the 7406, which according to the schematics is > correct. > > Anyway, having removed the 7406 and powered on the C64, it correctly > shows DEVICE NOT PRESENT. So my guess is the chip is bad. But that > wouldn't explain why 6 brand new chips fresh from the factory don't work. > My EPROM programmer will test 7406 Logic, if you want to know if it's bad send me an email (remove DELETE)and I will give you my address.
From: Garberstreet Electronics on 6 Nov 2009 13:33 "Webster" <timwmDELETE(a)pgtc.com> wrote in message news:gpidnZqRd_R392nXnZ2dnUVZ_jSdnZ2d(a)pgtc.com... > Paul F�rster wrote: > >> ... oh, this is strange. The C64 wouldn't show a picture without the 7406 previously. Now it does. Don't aks me why... You made >> me curious to give it another shot and so I removed the 7406 again and now the C64 properly powers on. >> >> I've cross-checked all combinations, not just neighboring lines of the serial connector and the 7406 socket each. There are no >> other shorts than pin 1 and pin 5 of the 7406, which according to the schematics is correct. >> >> Anyway, having removed the 7406 and powered on the C64, it correctly shows DEVICE NOT PRESENT. So my guess is the chip is bad. >> But that wouldn't explain why 6 brand new chips fresh from the factory don't work. >> > My EPROM programmer will test 7406 Logic, if you want to know if it's bad send me an email (remove DELETE)and I will give you my > address. I'm not a big Commodore guy, but a chip is a chip, and I'd suspect that there is a short preventing the 7406 from functioning properly, or it is blowing the chip as soon as it is powered up. At least he has narrowed this down to a single location. Now to find what it is that's causing it. Bill Garber of Garberstreet Electronics http://www.garberstreet.com
From: Paul Förster on 7 Nov 2009 02:17 Hi Webster, On 2009-11-06 19:34:29 +0100, Webster <timwmDELETE(a)pgtc.com> said: > My EPROM programmer will test 7406 Logic, if you want to know if it's > bad send me an email (remove DELETE)and I will give you my address. .... thanks very much for the offer. But sending ten chips to you just for testing would be a bit overkill. You are in England, right? I live in Switzerland. Buying ten new chips takes only a day and not two weeks and is ten times as cheap. :-) Still, thanks very much. -- cul8er Paul paul.foerster(a)gmx.net
From: Paul Förster on 7 Nov 2009 02:23
Hi Bill, On 2009-11-06 19:33:16 +0100, "Garberstreet Electronics" <willy46pa(a)comcast.net> said: > I'm not a big Commodore guy, but a chip is a chip, and I'd suspect > that there is a short preventing the 7406 from functioning properly, > or it is blowing the chip as soon as it is powered up. At least he > has narrowed this down to a single location. Now to find what it is > that's causing it. .... well, I think, with Ruud's tip about the CIA -> serial port pin test, I can narrow the problem even to the pins 3, 4, 8, 9, 12 or 13 of U22 because these pins would be the ones affected when bending the CIA pins away. Funny enough, the DEVICE NOT PRESENT message appears correctly if I bend *any* of the pins 5, 6, 7 or 9 of the CIA away. Still, the remark about blowing the 7406 when powering up is very important. Let's just hope that this is not the case. -- cul8er Paul paul.foerster(a)gmx.net |