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Indiana Warmech and The Last Crusade, Or, Obtaining My Final Grail Item: A Lisa 2

warmech

Well-known member
I would suggest that the 5V (main) resistor be higher power rating than the 25W you are showing. Thw 25W power rating is a maximum, and running resistors at their maximum power rating is a little questionable. At the very least, it will run very hot, at worst, if the 5V is a little high (anything higher than 5.0V), and you are risking a burn up/meltdown or the resistor if you apply power for anything but a very brief amount of time. I would also suggest that you up the power rating on the +12V also be raised, and would think that the resistors for the -12V, -5V for those rails can be safely reduced to 5W, or even lower. Does the Lisa actually have a +33V rail, or is it a 3.3V rail.

I am making the assumption that the Chosen Resistor (Amps) is actually in Watts, not Amps.
Yes, watts - my bad on that one. Good point on bumping that up a bit.

As for the 12Ohm/15Watt resistor, I'd originally pegged it at 12W, but Mouser only had a 10W or 15W as the nearest values, so I opted for the slightly higher value. I may see if they have a slightly higher value, then.

As far as 33 vs 3.3, yep, it's 33V. I'm guessing that's a driver (along with the 300V rail) for the CRT chassis.
 

warmech

Well-known member
Okay, the results are in! I assembled a load tester (pics below) and got the following voltages before the fuse blew again:

+5v rail: +8v
+12v rail: +18v
+33v rail: +53v
-5v rail: -5v (one success, at least)
-12v rail: -18v
+5 standby: +5v (5.5, but, eh)

The same two caps puff up after a very short while and, while they still appear to be functional at the moment, will probably fail shortly. I must admit that I'm a bit confused as to where to look next; this is farther into PSU territory than I've ever waded before. :(

Edit: I suppose the biggest question on my mind at the moment is how potentially damaged could things in the Lisa be given these readings?
 

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stepleton

Well-known member
Just to check first: are you connecting the +5V sense line (connector pin N) to +5V? If not, the PSU might be thinking that it's undervoltage, and so it's pushing more and more power into the transformer to try and turn +0V into +5V.

The rest of this post assumes that you are doing this.



Yeesh, assuming your loads are set up correctly (looks nice btw! much tidier than mine), that's a spicy PSU, going overvoltage by 60%. I think it's fair to say that it's not regulating, but what is also interesting is that it isn't shutting itself down owing to the overvoltage (Hardware manual PDF page 272, crowbar circuit mentioned at bottom). I would expect that +18V on the +12V rail would be enough to trigger the shutdown mechanism and, since that's not happening, would at least suspect something fishy might be going on with CR9, CR10, or its neighbours in the circuit.

To be clear, this problem isn't what's causing the overvoltage in the first place: it's a secondary problem in that the PSU does not seem to be ready to shut itself down if an overvoltage condition is present.

While I'm stalling for time, we can answer some other questions that aren't really relevant. +5V standby is actually a completely separate power supply within the power supply housing. It's a simple linear supply, and it's not too surprising that it works. (PDF page 273, "The Standby Supply".) Similarly, -5V is working because it uses a simple linear DC-DC voltage converter that changes whatever's on the -12V rail to -5V. Owing to the nature of how linear voltage converters work, it's going to be working harder to convert -18V to -5V than it would to convert -12V to -5V (and would get much hotter in the process), but your PSU is probably not staying on long enough for this to matter.

I'm afraid my own PSU repair skills are somewhat limited too --- there's a chance someone might jump in with some better ideas. It's fair to say that the Lisa PSU is not made in the way that more modern PSUs are, not that this would help me too much. Therefore, as we ponder and await an expert, why don't we collect what information we have first?

- Using the old Mark One Eyeball: take a very good look at the components on the board. Aside from the bulging caps, does anything look unwell? Are there parts of the board that seem to look scorched? Anything that seems cracked or fatigued? Solder joints seem ok?

- When you were running the PSU: did you notice anything that might be a clue? Stuff getting hot? Buzzing sounds? (Many Lisa 1.2A PSUs do buzz, so that might not be so unusual.) Smoke? Odours?

- As a kind of hail mary: what's going on with R29, the voltage adjustment trimmer? (PDF page 269, also schematic bottom right) Maybe it's just preposterously out of trim --- is it set all the way to the stop in one direction or the other?

Another recommendation is: hit the books. Have a read of Chapter 10 of the hardware manual, which narrates how it works. Don't worry if you can't understand everything (I don't either!) --- although maybe your TV repair experience will help. Form some theories about things that might be going wrong, theories that sound like "maybe if this component is always on, then the primary side will keep pumping energy into the transformer". These components may be dangerous to check in circuit without special equipment (DON'T just plug in an ordinary oscilloscope and start looking for the waveforms on PDF page 268!), but one thing I could do is take some power-off measurements of those suspicious components in my own working spare 1.2A PSU, and we could compare if we're seeing the same things.

Finally, you might consider starting a conversation over on lisalist2, where there really are some talented people who might be able to come up with an answer more promptly.



Unfortunately, you are correct to be concerned that the excessive voltages might cause trouble. -12V is probably not used for much that you have to worry about; -5V is fine; +33V is your screen which you said was at least coping briefly. +12V and +5V are likely giving all your logic a hot time. Hopefully it was brief enough that no substantial damage has been done.
 

warmech

Well-known member
Well, I was a dunce and did not have the +5v rail hooked up the the +5v sense line. No improvement after having done so, but it did need to be done.

Regarding your other questions, though:

- There is one scorched spot, but the components on top of it test fine (see the attached image). The resistor there was falling apart, but tested on point; I replaced it anyway just to be safe. At this point, virtually every solder joint has been reflowed, so they should be good as well. There were a number of pads that bit the dust when replacing caps, but they've been tested for continuity and check out fine as well.

- The PSU is back to chirping, which is odd; it wasn't doing that originally after recapping (see attached video)... Of peculiar note, however: I went to feel if Q1 was hot (both the heatsink and the top of the bottlecap itself) and got a little tingle. That seems... like it shouldn't be happening? Also talking with a gentleman on facebook about this and he just remarked that he didn't know why that would be happening. Possible next lead? He also was curious about CR17, which looked like it tested okay, but I have a couple replacements; I could swap one in and see, maybe?

- Thought of that earlier as well and it turned out normal, (un)fortunately.

I'll start combing through chapter 10 and give a friend a call who might be able to take a look locally. He's the guy who taught me everything I know about repairing arcade games and CRTs, so he may be willing to put a set of eyes on this as well. Regarding lisalist2, my confirmation just got approved, so I'm going to start a thread over there as well.

On the matter of potential destruction - well, I guess it is what it is. I pulled some 74XX ICs and they tested fine, so maybe it's all good. I can get my friend to test some of the RAM as well and see about that. He's got a Fluke CPU/Bus tester and logic analyzer, so I may get him to clip it on and see if the CPU ate it as well.

I really and sincerely cannot thank you enough for helping me with this - it really means the world. Also, I'm trying to catch any typos, so bear with me if I missed any. My right hand's pretty heavily bandaged, so I miss some stuff here and there.
 

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stepleton

Well-known member
Gotta run now, will say more later, but that toasty resistor you've spotted has been toasty in other 1.2A PSUs I've encountered, and I think it's just a weak spot in the design. Maybe not a problem. In one PSU, I've replaced a much sicker-looking resistor there with something beefier, stood off from the PCB like its neighbour.

(There's a chance though that this resistor getting hot is a symptom of another problem, and my replacement just wallpapered over whatever it was.)

I'm not sure I'm too surprised if Q1 is tingly, although be careful poking around in there! The case to Q1 is the transistor's collector (datasheet), and so you're doing the same here as touching pin 24 of the transformer. If this transistor is switching current (which it is!), then you might indeed get a tingle from that --- after all, it's just a few hundred volts peak-to-peak high-frequency AC!

More in a while. Keep puzzling over the problem: remember, we know the switching power supply is switching, it just doesn't seem to be regulating, that is, tapping the brakes on pumping power into the transformer once the output lines get up to the correct voltage.

Hope your hand gets better soon! See you on lisalist2...
 
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cheesestraws

Well-known member
Of peculiar note, however: I went to feel if Q1 was hot (both the heatsink and the top of the bottlecap itself) and got a little tingle

A quick but important side note:

It is not at all unheard of for heatsinks/cans to be at line voltage in older PSUs. One of the transistors in the Mac Plus/512/128 PSU has its heatsink live, for example. You can't even really assume it's safe to touch passive bits of metal in these things unless you've verified it :\
 

warmech

Well-known member
after all, it's just a few hundred volts peak-to-peak high-frequency AC!
Oh, that's all, lol? :p

In all seriousness, thanks for pointing that out (same to you @cheesestraws). My assumption that the on/off switch would have killed that part of the PSU was apparently bad, so thank y'all for clarifying that! I guess that makes me wonder, though - if the PSU was "off" (plugged into power, but not powered on by way of the on/off switch), would/should it [Q1's case] still be energized? I had assumed that with the power off there would be no power running through that part of the board. This is why I hate working with power supplies. :(

As for that resistor, I've seen a couple photos of other boards as well with similar scorching - I'm with you on the idea of it being a weak spot, though not necessarily a failure point.

Also, I may take you up on your offer to measure values off your known good components, especially ones like CR17, and CR8-11.
 

stepleton

Well-known member
Oh, I missed that the power supply was off! In that case, I am less certain what's going on, but yeah, poking around with the mains attached is potentially a risky thing to do, especially in a power supply that can turn itself on. CR2 ought to be deactivated because U3 ought to be deactivated. Bet it all on double-ought :) (not trying to be mean, I just like the pun!)

(How much do you trust the mains wiring in the place where you're servicing the power supply? Is there a chance that hot and neutral could be reversed?)
 

warmech

Well-known member
Oh, I missed that the power supply was off! In that case, I am less certain what's going on, but yeah, poking around with the mains attached is potentially a risky thing to do, especially in a power supply that can turn itself on. CR2 ought to be deactivated because U3 ought to be deactivated. Bet it all on double-ought :) (not trying to be mean, I just like the pun!)

(How much do you trust the mains wiring in the place where you're servicing the power supply? Is there a chance that hot and neutral could be reversed?)
Hehehe, I appreciate the pun. And it should be wired correctly - I just built the shop I'm working out of a couple months ago and triple-checked my wiring was up to code before insulation and drywall went up.

Edit: Completely unrelated, but this thing has an 800K floppy in it. I wonder if it got upgraded at some point. It's just a ROM swap, right?

Double-edit: LisaList2 thread posted...
 
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warmech

Well-known member
Last message for the day (since I can't edit the previous one): I'm ordering a couple MPU-131s just in case, but rdmark over at TinkerDifferent posted this in the corresponding thread earlier:
Another tip that I read in a thread somewhere on Lisalist, is that the optocoupler on U3 may go bad with age and cause voltage issues. It has an LED inside the package with wears out with heavy use. And supposedly (this is 2nd hand information) it is in charge of decoupling the hot and cold side of the PSU and a failure mode is that the voltage on the cold site get ramped up beyond spec. I preemptively replaced the one in my PSU with one from this eBay seller.
While I'd rather not spend $30 on a relay, is there some credence to this? The schematics don't otherwise look like it should cause power to ramp up on the cold side in the event of a failure, but I'm not exactly an expert on all this. Heck, I figured U3 was just the relay to power on the machine.

One last thought - R29. I replaced it just to see if I was crazy and got the same result - zero change in voltage whatsoever no matter how it's adjusted. It seems like the sense line (and the pot, by extension of that) is just not even factoring in at this point. I pulled Q2, Q3, and Q4 again just to check them one more time and they all test good. CR8, 10, and 11 aside, the only other thing I can't test is CR21 (one of the MPU-131s), but I'll have a NOS one to drop in sometime this week. If you get the chance to measure CR8, 10, and 11,I'd be incredibly grateful. I've been combing the local facebook groups for anyone in the Dallas/Fort Worth area with a Lisa and so far it's coming up a bust, so anyone that can put hands on a working PSU for me at this point is my hero. Also, (final, final though) it's like the shutdown circuit isn't even functional, so I'm curious of CR10 is just shot.
 
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warmech

Well-known member
Minor update - the crowbar circuit has been fixed. A bad trace on a cap was causing it to have no path to ground. One fixed, it was back to the expected chirping of a PSU in shutdown. More to come!
 

CC_333

Well-known member
What's up with the new caps puffing up like that? That doesn't seem like a good thing....

c
 

warmech

Well-known member
What's up with the new caps puffing up like that? That doesn't seem like a good thing....

c
Fixed now - it was related to the bad ground trace for the crowbar circuit. Why those two only and not C20 I have no idea but the issue is fixed now, thankfully. Still stuck in shutdown but not overvolting the hell out of itself, at least.
 

CC_333

Well-known member
Yes, definitely. I'm glad you fixed the crowbar, at least, so now it's safely doing it's thing rather than letting things blow up!

c
 

mg.man

Well-known member
Firstly, congrats on progress so far!!
I recently acquired a 2/10 that had been languishing in an outside shed for at least 10 years. At the time, I was worried I'd run into battery damage, but seem to have escaped that since the 2/10 I/O board didn't have them... Even so, I have discovered the card edge connectors have rotted and need replacing... 😞
I've removed the large connector and cleaned either side of the board where it was.
Great work... how did you go about removing it so cleanly? And have you managed to sort out the PSU issue?
 

warmech

Well-known member
Firstly, congrats on progress so far!!
I recently acquired a 2/10 that had been languishing in an outside shed for at least 10 years. At the time, I was worried I'd run into battery damage, but seem to have escaped that since the 2/10 I/O board didn't have them... Even so, I have discovered the card edge connectors have rotted and need replacing... 😞
Great work... how did you go about removing it so cleanly? And have you managed to sort out the PSU issue?
Thanks! I used a Hakko FR300 to desolder it; it went fairly quickly, considering it's a four layer PCB and there's like 120 pins, lol. If you do a lot work on stuff like this and don't have one, get one. Of all the tools I own - electronic or otherwise - my Hakko is without a doubt my most valuable and loved for what it does. I originally bought it for working on arcade PCBs and RGB monitor chassis, but it's bled over into pretty much anything electronic I work on. Just make sure you're using enough heat (but not too much) and that the gun tip is clean or you'll rip pads off... like I did with two of them. They were easy to repair, thankfully.

As for my PSU, I've officially sidelined it; as soon as I fixed one issue, another one popped up. Once that got fixed, the original issue returned and it went straight back into overvolting. To take it's place, I repurposed an ATX PSU with a voltage booster to crank out +33V for the monitor chassis and it's been running okay for testing other repairs. Once I get more of this thing working, I'm going to try to sit down and work on figuring out some kind of replacement PSU for this thing.

If the connectors are all that need replacing, then you're actually pretty far ahead of most folks. Battery damage has killed more of these things than just about anything else at this point, I'd wager. The card pins are probably fine and a fiberglass pencil should de-crudify them of any rot from the connector. My I/O board had some pretty serious corrosion around the pins due to the battery and only one turned out to need replacing once I got them clean. If the motherboard is also too weathered to resurrect, worry not. I believe replacements can still be had from VintageMicros but, if not, that provides a nice segue into a related topic.

I'm working with someone else to reproduce the entire card stack so, hopefully, by the end of the year anyone with the need should be able to download gerbers for any board in the stack and have them reproduced as needed. When I have some made up later this year for testing, I'll be selling the extras. I've got the RAM card done and will be working on the CPU card next. AlexTheCat123 over at LisaList has already completed the motherboard and parallel card. With any luck, the I/O and CPU boards will be done in the next few months and we can move on to testing everything. Literally the only thing that can't be sourced is an original COP421, but even that can be worked around with a COP replacement board.
 

mg.man

Well-known member
I used a Hakko FR300 to desolder it
Good to know. I do have a similar de-soldering station - no-name brand, separate main unit/vacuum. Not integrated like the FR300, but, like you say, having something dedicated to de-soldering is SO much easier than using solder wick, etc... wish I'd gotten one years ago.

What I was actually more interested in was your technique. Did you just leave the connector intact and rely on the de-soldering gun to pull all the solder out? Since you mentioned the risk of sucking the pads off, perhaps the Hakko has a stronger vacuum than my no-name? What I've found with mine is that it won't get enough solder out - especially on a connector that size - to make it an easy extraction, so I ended up destroying the connector so I could attack the pins one by one. It worked, but I did cause a bit of damage that needs patching up. Should be OK. 🤞

As for my PSU, I've officially sidelined it
Ugg... sorry to hear... good luck for when you revisit!

If the connectors are all that need replacing, then you're actually pretty far ahead of most folks...
I do count myself pretty lucky atm... not only did I find my Lisa for a sum that did not break the bank, I was also connected to another guy who had a spare chassis and motherboard, so I've been able to get "a" Lisa (mostly) working with my boards. I'm hoping to resurrect my motherboard so I have a spare.

provides a nice segue into a related topic ... I'm working with someone else to reproduce the entire card stack
Yes, I'm watching that with keen interest!! I was the guy that mentioned VintageMicro's 2Mb boards - which he didn't actually have. :confused: Glad to see someone had scans and super exciting you're reproducing it! DO count me in when you're ready for testing or just need to recoup some cost. I have STACKS of 256Mb Mac SIMMs that came out of Plus's and SE's that need to be put to use.
 

warmech

Well-known member
Good to know. I do have a similar de-soldering station - no-name brand, separate main unit/vacuum. Not integrated like the FR300, but, like you say, having something dedicated to de-soldering is SO much easier than using solder wick, etc... wish I'd gotten one years ago.

What I was actually more interested in was your technique. Did you just leave the connector intact and rely on the de-soldering gun to pull all the solder out? Since you mentioned the risk of sucking the pads off, perhaps the Hakko has a stronger vacuum than my no-name? What I've found with mine is that it won't get enough solder out - especially on a connector that size - to make it an easy extraction, so I ended up destroying the connector so I could attack the pins one by one. It worked, but I did cause a bit of damage that needs patching up. Should be OK. 🤞


Ugg... sorry to hear... good luck for when you revisit!


I do count myself pretty lucky atm... not only did I find my Lisa for a sum that did not break the bank, I was also connected to another guy who had a spare chassis and motherboard, so I've been able to get "a" Lisa (mostly) working with my boards. I'm hoping to resurrect my motherboard so I have a spare.


Yes, I'm watching that with keen interest!! I was the guy that mentioned VintageMicro's 2Mb boards - which he didn't actually have. :confused: Glad to see someone had scans and super exciting you're reproducing it! DO count me in when you're ready for testing or just need to recoup some cost. I have STACKS of 256Mb Mac SIMMs that came out of Plus's and SE's that need to be put to use.
As far as technique goes, I was able to get the solder out of most of the holes, but some - anything connected to an inner plane, for instance - were particularly stubborn. As the connecter had to be replaced and I didn't want to risk damaging any further pads/traces, I just mangled the connecter at the few remaining pins and used a soldering iron to heat up and pull the last 4-5 pins manually. If I were going to me much more careful (like if I were trying to preserve the connector), I would have pulled as much of the original solder off as I could; flooded the pins with fresh solder; made sure the tip of the desoldering gun was very clean and in good shape; and left it sitting on the pin much longer than normal (several seconds, as opposed to a few). If that still didn't get it all, I'd dial up the heat in very tiny increments until I found an amount that worked. The really stubborn pins on any multi-layered board are going to the power and ground rails, as you just have to dump that much extra heat into those layers to overcome the heat-sink effect they produce. Once you find the right amount, though, it's just a game of patience.

As long as your gun is producing consistent heat and can draw a decent amount of suction, a no-name brand is perfectly fine! Heck, my soldering iron is some el cheapo deluxe, fly-by-night brand and it works great! It was cheap enough that if/when it dies I'll give it the ol' college try to repair it but, if it's unserviceable, I'll just replace it. I used to have a Pace industrial workstation that a friend gave me as a sort-of "my first big-boy soldering iron" but the one tip I had for it died after years of loyal service. It turned out to be far less expensive to buy a whole new iron with more features and tip interchangeability than to replace the one tip for that Pace iron - and I probably gave ~$70 for my new iron. I was sad to stop using it (and still have it, in case I ever come across a cheap tip for it), but my current one is doing exactly what I need at a price point I'm comfortable with, lol. Since Hakkos have come down in price, I may just get one of those next.

As far as the motherboard goes, you're probably fine. Just make sure you have good continuity with any damaged pins/pads/vias and that they don't short to ground or power and you should be home free. I'm glad you were able to get a Lisa in relatively decent shape and locate spare parts and do all that for a decent price. That's getting progressively harder these days (as with everything else in this hobby getting more expensive).

Also, I apologize for not recognizing your name from the other thread, lol! :p So do you currently have a working Lisa? If so, I'll make sure to get a SIMM card out to you for testing when they're in my hands. I'm probably not going to send out a 512K Apple card or 2MB AST clone I'm working on as well due to my having a sense of empathy and not wanting folks to either have to solder on ~90 IC sockets or source 72 4164/41256 DRAM ICs. I have a source for bulk DRAMs but the price for 72 of either of those would cost about as much as a set of four layer PCBs. Meanwhile, I have a stack of 256K parity SIMMs sitting in a box a few feet away; I think most folks can relate to (and would rather deal with the latter), lol.
 
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