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512k sweep/power supply help

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I replaced the two 100uf 200v caps. and reinstalled Q11 then started it up and It sparked just like before but dimmed slowly. I also noted that the brightness knob on the front seemed bad and would flicker brighter and then darker as it faded slowly, I also noted that the sides were waving in and out (like water) I will replace more caps I have here and see if it gets better.

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Tom, I wouldn't be surprised if Pina was in error because I've spotted other errors in his books. But for the most part, his information is quite accurate.

 

Pina says Q11 is to be rated at 12A. So when I looked up those Apple OEM "replacements" listed in his book, I too thought he would be in error because the data I see shows them to be rated at only 7A. However, I believe Pina is simply saying that those 3 parts are "what he himself has seen in various Apple analog boards through the years," and he therefore deems them "OEM replacements." Pina then offers the Philips ECG379 part as a proper 12A replacement.

 

So I think going with the Philips part or similar is the most prudent choice.

 

I heartily agree that Pina is to be trusted in most matters. I suspect that he was subtly (or not so subtly) guiding the user to an upgraded part. In switchers, however, there is a tradeoff among the various parameters, and it's not always better to seek a higher-current part. In switchers, there is considerable dissipation in the transition between states, so switching speed is important. Higher-current parts can be more sluggish, and using them can actually be self-defeating. Given that Q11 seems not to have any unusual failure modes, I'd normally be inclined to leave well enough alone.

 

That said, it appears, from what you've found from Pina, that Apple used a variety of transistor types for Q11 (I myself have not noticed this, so thanks for letting me know), so evidently any of the ones he cites have been proven to work well.

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Multimeter with transistor tester.

 

Yes, but how did you use it? Did you remove the transistor first? Or did you leave the transistor in circuit? The only reliable way to test a transistor is out of circuit. If you do it in situ, the test can be confounded by other things tied to the device.

 

From the intermittent behavior you are reporting, it's highly unlikely to be a transistor problem. Transistors rarely "fade out" repeatedly in this manner; they either work, or die. :)

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I removed the transistor completely and used it as the instructions say to and it had no response at all not even a blip, I used it to test a good one the day before so I know it works and its only 4 days old (the multimeter). It is odd though my board did not have a connector to the Collector or middle pin is was just in a hole on the board with no solder or leads anywhere near it so I assume it is not meant to be connected. is there a proper schematic for this analog board, that pdf shows Q11 having all 3 pins connected.

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Yes, all three terminals of the transistor are used. :)

 

The middle terminal is electrically connected to the tab.

 

I still have lingering doubts about the test. It is very rare for a transistor to behave in the intermittent way you describe. As I mentioned, either a transistor works, or it is dead. It is extremely unusual for a transistor to go back and forth between these two states. I cannot recall ever having encountered this myself. Indeed, I can't recall even hearing about anyone else encountering such a phenomenon. Depending on the precise method used by the multimeter, it is possible to get a false result. In the case of power devices, it is frequently adequate to do the following:

 

1) Check for a good diode between base and emitter.

2) Check for a good diode between base and collector.

3) Verify that there is no continuity between collector and emitter.

 

You also mention sparking. Is this something you see, or is it something you hear?

 

And have you looked very carefully at C1? Is there *any* bulging on the top?

 

Have you carefully inspected the yoke connector? Not only should the connections on the analog board be resoldered, but you should also unmate the two connector halves and inspect all 8 of the pins for signs of arcing, melting, oxidation, etc.

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Yes, all three terminals of the transistor are used. :)

 

The middle terminal is electrically connected to the tab.

 

ah ok I should have figure.

 

I still have lingering doubts about the test. It is very rare for a transistor to behave in the intermittent way you describe. As I mentioned, either a transistor works, or it is dead. It is extremely unusual for a transistor to go back and forth between these two states. I cannot recall ever having encountered this myself. Indeed, I can't recall even hearing about anyone else encountering such a phenomenon. Depending on the precise method used by the multimeter, it is possible to get a false result. In the case of power devices, it is frequently adequate to do the following:

 

1) Check for a good diode between base and emitter.

2) Check for a good diode between base and collector.

3) Verify that there is no continuity between collector and emitter.

 

yeah It is a cheap multimeter has worked every other time I have used it, but who knows. I will recheck it with another meter that has a diode check.

 

 

You also mention sparking. Is this something you see, or is it something you hear?

 

Well its when I turn it on so I can not see it, but the other day I had it opened and discharged the crt and it was just sitting there and it sparked

around C35 C36 and Q11 area that one I saw out of the corner of my eye and I could hear it.

 

And have you looked very carefully at C1? Is there *any* bulging on the top?

 

Yeah It looks ok I do not think I have a replacement (or 4 1uf disk caps)

 

Have you carefully inspected the yoke connector? Not only should the connections on the analog board be resoldered, but you should also unmate the two connector halves and inspect all 8 of the pins for signs of arcing, melting, oxidation, etc.

 

is this J1 you are talking about, I did test from the solder up to the yolk for continuity and they all were ok with no resistance. (The pins are not real but are nails I used that fit snug into the other side since I do not know where J1 went after it was removed from the board a long time ago) I did not think these had enough juice to ark to other parallel pins (I assume you mean ark to the corresponding connector and not to parallel pins) I could use some electrical tape to insulate them more and see if that helps.

 

Also should I try to find a real replacement for the C6 I made and posted about?

 

Quick stupid question I am in need of C6 and its a 22uf 50v and I have 2 10uf and a 2.2uf that are 50 or higher volts will the extra 0.2uf going to be too much extra tolerance for the 512k if I install them in parellel? I can always use 2 1uf ones but I would like to put as few in there as possible and I do not want to order one capacitor online and get charged a bunch for shipping. Radioshack has them but only in 35v (they are so lame) I do not think it will be but I just wanted to check.

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I put some more caps (noticed one was a bit swollen at the top not enough to notice unless I looked real close) I had in it, took out the transistor and tested it again it was good, (even the transistor tester that said it was good worked so it must not have been connecting properly)

re did some of the solder and it turned on and seems to be stable (now I have to fix the (floppy and the brightness dail on the front) and it should be useable.

 

Thank you everyone that posted here to help me. I feel accomplished this week (fixed a lisa and a 512k mac) I must be stuck in the 80's.

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it does seem to fade slowly still but does stay on. I have a feeling its just the brightness knob as I said above. I have some knobs from the IIc monitor maybe one will work.

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I actually fixed the drive today. I used silicone lubricant (the store was closed to get the lithium white lube that is suggested) but I cleaned it first (with alc.) then lubed it with the silicone cleaner/lube spray I had. I worked it in until it became mechanically sound. I also replaced the missing felt pad with one from a disk ][ drive and put it back together and read the first disk I put in it. I am going to wait on the brightness knob since I am getting a brand new analog board (along with a mouse and keyboard) and I am going to use this repaired one as a back up. I did adjust the max bright and it seems to be nice and bright (probably a bit too bright) I will adjust it later. Also I seem to be getting weird feedback from the floppy drive. It does make some cool noises though. Thanks for the links I did see the 400k drives but It seems I have fixed mine I do not know yet if the one in my lisa works but we will see when I get some disks made on my 512k. It should work great for making the disks (lisa websites state the best machines besides lisa's to make disks on are the 128k, 512k, plus since they have the 400k drive)

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I found a kind person to send me one for a good price with a keyboard and mouse. not nearly that much. the ones on ebay are way over priced. I was waiting for a mac plus to take one out of but a brand new one is even better.

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I am getting a brand new analog board (along with a mouse and keyboard)

"Brand new"?

 

Those do crop up on EBAY about once a year. I know because I purchased such an Apple Service part, never used before, on EBAY in the past. But they are rare. And I must say that I was simply "blessed" the day I bid on it as others clearly did not spot that auction. If they had, I certainly would have been outbid. I only paid $35 for it. But it cost me another $35 to ship to Japan.

 

But if you mean you are buying a "used, but good condition" analog board, you still have to beware. Because any "used" board technically could have been "abused" as well. In such a case, your situation would not be different from now, and you would still need to replace some parts. At minimum, C1 needs to be replaced on many boards.

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no it was a sealed service part (had to take it out of the box to fit in the shipping one with the keyboard) I told him I would feel bad using it but I got such a good deal I could not say no and he said he just wanted it to go somewhere where it would get used.

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After you replace the analog board, you should use your HD 20 and a 800k drive for a nice setup!

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I have two 3rd party 800 drives and a numeric pad that I am going to put with it too. I just need to get some files on to the HD20 for making my lisa disks, the first way I tried did not work so I will have to try some others.

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the new board showed up today and worked great. (I have to adjust the image a bit) I also had to shorten the mouse cable about 5 inched because of a break inside cause one of the axis not to work but now it works great. now I need to figure out how to get me disks made on one of my other macs.

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Now tell me, who could have caused so much damage to your Lisa and 512k? Seems like the old owners were sadistic Windows fans or something.

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well the lisa I found in a pile of free stuff one day, very lucky I may add, with some kind of sticky pop residue ALL over it, still the faint spackle of silver paint on part of it (the place I got it was used by this guy here who has a van covered with circuit boards that is probably where the Memory and Cpu boards went). the 512k was acting up and that was my fault that the analog board got stuff picked off of it. but I set it right and fixed it :) whats the best way to adjust the picture, is it ok to do it while it is turned on, and how should I prop it up without the case?

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finally got the HD-20 to boot (Had to dig for some Low D disks for the 512k) I am going to be asking in the trading post about some new 400k disks for the 512k and lisa.

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You'll be hard pressed to find 400k disks. But 800k are all you need. Just format them as 400k, since you only need 1 side of the disk. And the nice part is, should you every want to reformat them as 800k, it's a snap! You can also use 720k PC disks, if you can find them.

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