Phantom drive?
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From: Paul Förster on 9 Nov 2009 14:02 Hi Andreas, On 2009-11-09 09:26:25 +0100, Andreas Beermann <andreasbeermann(a)lycos.de> said: > Hallo Paul, > to make the search more systematic please try to do the following: > 1. check if you've connected something to the user port that's > fiddling arround with pin 9 which is shared with the ATN pin! .... there's nothing there. In fact, the user port pins have been cut off the edge of the board. > if no: > 2. please check if it's OK after removing CR9,CR11-17. If yes, re- > insert one diode after the other (polarity must be correct!) or Simply > replace all with new diodes (could also be a 1N4148) .... "unfortunately", the diodes are good. I took them out as you said and checked them. They block in one direction and show a drop voltage of 0.53V on the other direction -- all eight of them. > if no (do NOT re-mount the diodes so far!): > 3. remove capacitors C88 and C94 and check if it's OK thereafter. If > yes, replace with fresh ones .... also, no effect. :-( > if no (do NOT re-mount the capacitors so far!): > 4. remove the CIA, U22 and RP6. Now all signals of the serial port > (except RESET) should not have contact to *anything* (with the diodes > and capacitors removed as well!) .... I did, as you requested. No effect other than that the C64 won't power up without RP6. Why is that? Is that because pin 3 of RP6 connects to /RES (pin 34) of the CIAs? Putting it back in (temporarily) made the C64 power up again. Caps and diodes are still removed. No change. As I mentioned above I needed to put in RP6 to power it up and check with the LOAD command. > In case you measure any Ohm-value < 100kOhms from any of the serial > signals to ground you have detected a shortage on the board. .... no, everything seems fine, except something I don't understand: CR9 and CR14 have a measurable resistance between anode and cathode, *with the diodes removed!*. The resistence between both pins of CR9 is ~3.3k Ohm and the resistence of CR14 is ~3.6k Ohm. Does that effect maybe come from C4, RP3 and the connection to pin 24 of CIA1? > see if that leads you any further... .... up to now, unfortunately not. The only knowledge I can reliably draw from this is that the C64 won't power up without RP6 in place. I run out of ideas. :-( -- cul8er Paul paul.foerster(a)gmx.net
From: Paul Förster on 9 Nov 2009 14:24 Hi Peter, On 2009-11-09 03:54:40 +0100, schepers(a)ist.uwaterloo.ca (Peter Schepers) said: > It's a bit of work what you're proposing. You will need to wire the > outputs from the 7406 to a serial port as well. You can eliminate the > diodes from your test, though. .... yes, I know about the lines. In fact, it should only be 5 lines to the CIA, VCC and GND, also three 1k resistors and the C94 replacement. > Thinking about the diodes... have you checked all of them? They are there > for over/undervoltage spikes. It's easy to verify they are OK with the > diode checker on your multimeter. .... I did. All of them block in one direction and show a drop voltage of 0.53V in the other direction -- see my answer to Andreas' post. > With enough bending out, the pins will break off. Be careful. .... yes, I know. That's why I plan to use a socket for the experiment. Sockets are dirt cheap and I have plenty of them. > What I mean is to make sure that the voltages on each pin seem right. 5V > and GND are easy. The 7406 is an open collector inverter so it needs the > 1k pull-ups for proper operation. If pin 1 (input) is low, pin 2 (output) > will be high and vice-versa and for each inverter set (3 in/4 out, 5 in/6 > out, 9 in/8 out, 11 in/10 out, 13 in/12 out). .... ok, I did check this. All pin pairs 1/2, 3/4, 5/6, 8/9, 10/11, 12/13 are always the complement of each other, pins 7 and 14 being VCC and GND. 1 is 4.98V, 2 is 0.xx mV, and so on with each pair. > If you're not using the port, the voltages on the pins will not be > fluctuating. .... yes, I saw that. Thanks. > There's no 12v here. The diodes are in this circuit to prevent voltage > spikes (+ or -) to be absorbed. .... yes, I know. I was referring to over-voltage that could possibly fry a 74xx chip. But there's nowhere beyond 12V on the whole board, so even if there was a short, then it wouldn't be enough to fry a 74xx chip, right? > No, the 4066 is used as a switch for the POT lines. No relation. .... no, wait. There are two 4066! One is in U21, which I am referring to and the other is in U18 next to CIA1. The latter is for POTXY. The former has direct connections to U7, U8, U6 and to U19. If U21 is empty, you don't see a picture! > By slack joint, do you mean a bad solder joint? If you suspect one, you > can simply re-solder the joints. .... tried that but they measure ok. > I have no idea. I'm looking at schematic #252312 as it seems to match what > you have, and I see the "1" as well. Doesn't make sense to be. Even the > symbol for the inverter is non-standard. .... I took the ones from zimmers.net, put them together and printed them out on A3. Nicely and clearly readable. :-) But yes, I would have expected a triangle or that half round thing for gate symbols but they use rectangles there. That doesn't confuse me much. What confuses me is the "1" printed inside the rectangle. > Regarding your question about RP6 and the resistance difference on pins 4 > and 6... they are the only ones that connect back directly to the 6522. I > suspect that the port resistance is in parallel and changing the values. > Also, I assume you are checking things with no drive connected to the > serial port. .... there is no 6522 in a C64. ;-) Yes, I have no drive connected. But since I had to take RP6 out anyway, as suggested by Andreas, I checked it off board. And it's proper 1k Ohm on all pins. From my measuring experience today I take it that the presence of chips in the sockets can *drastically* influence values. So I can understand Andreas' desire to take off components to get proper results since today. -- cul8er Paul paul.foerster(a)gmx.net
From: Andreas Beermann on 10 Nov 2009 03:00 Gruezi Paul, > > if no (do NOT re-mount the capacitors so far!): > > 4. remove the CIA, U22 and RP6. Now all signals of the serial port > > (except RESET) should not have contact to *anything* (with the diodes > > and capacitors removed as well!) > > ... I did, as you requested. No effect other than that the C64 won't > power up without RP6. Why is that? Is that because pin 3 of RP6 > connects to /RES (pin 34) of the CIAs? Putting it back in (temporarily) > made the C64 power up again. The 64 was not meant to boot up with the CIA and other parts removed. I just wanted you to MEASURE the signal lines with an Ohm-Meter - they should have high impedance against everything. So just measure the resistance against ground. In case your Ohm-meter displays anything other than an open connection try to trace the line you have measured and check if there is anything else in that line. This is to check if the board/wiring/soldering is OK. > > ... no, everything seems fine, except something I don't understand: CR9 > and CR14 have a measurable resistance between anode and cathode, *with > the diodes removed!*. The resistence between both pins of CR9 is ~3.3k > Ohm and the resistence of CR14 is ~3.6k Ohm. Does that effect maybe > come from C4, RP3 and the connection to pin 24 of CIA1? for CR9 this is OK - you'd have to remove RP3 and CIA1 as well - otherwise you measure ~3.3k (which you actually do) - so this should be fine (you can x-check by removing CIA1+RP3 as well). For CR14 you should have high impedance with CR14+U22+RP6+CIA2 removed. In case not you might have narrowed the problem down to that line. Did you measure with these parts removed? Andreas
From: Paul Förster on 10 Nov 2009 05:16 Hi Andreas, On 2009-11-10 09:00:42 +0100, Andreas Beermann <andreasbeermann(a)lycos.de> said: > for CR9 this is OK - you'd have to remove RP3 and CIA1 as well - > otherwise you measure ~3.3k (which you actually do) - so this should > be fine (you can x-check by removing CIA1+RP3 as well). > For CR14 you should have high impedance with CR14+U22+RP6+CIA2 > removed. In case not you might have narrowed the problem down to that > line. Did you measure with these parts removed? .... yes, my measurements were with parts removed. The total of parts removed now is the following: CIA1, CIA2, RP3, RP6, U22, RP9, RP11-17, C88, C94 Readings are: Between anode and cathode of RP9: still 3.3k Ohm Between anode and cathode of RP14: still 3.6k Ohm What strikes me as odd is these two readings. The connections between anodes and cathodes of the diodes should be completely open now with parts removed, right? What strikes me as even more odd is, that Ruud's dead board, having done the same to it for testing and comparison except removing CIA1, also shows 3.3k between anode and cathode of *both* RP9 and RP14, and not just for CR9, which I would have expected from your above statement. Maybe my above readings are NO anomalies? -- cul8er Paul paul.foerster(a)gmx.net
From: Paul Förster on 10 Nov 2009 05:17
Hi Andreas, On 2009-11-10 11:16:06 +0100, Paul F�rster <paul.foerster(a)gmx.net> said: > CIA1, CIA2, RP3, RP6, U22, RP9, RP11-17, C88, C94 .... ouch! I meant of course CR9, CR11-17. Dito for the rest of my previous post as I was referring to the diodes of course. Sorry. -- cul8er Paul paul.foerster(a)gmx.net |