SE 30 focus problems after cap replacement

[garyg42]

After excellent dealings with Trag, I replaced (paid technician) to have caps replaced with tantalums. Fixed problem, but now focus is off a bit - but too uncomfortable to view. The Focus Adj. pot does nothing. Asked Trag, and in a most timely answer he told me it was probably fixed resistor.

He wrote: "If the focus is poor and adjusting R27 does not help, then most likely R26 is burned out (open). R26 is a 1 M ohm, 1/2 watt 5% resistor on the analog board."

Has anyone else had this problem on SE 30, and can you confirm what Trag said?

If you reply to MLA, can you also please send to?:

garygphotog@shaw.ca

I'e been having A LOT of trouble logging into MLA.

Great Thanks

Gary Greenspoon

 

[JDW]

Pulling the logic board and replacing caps should not affect your screen focus at all. I should know since I have yanked out my motherboard and put it back in dozens of times without disturbing the screen at all.

And although it could be a bad component as trag said, it could also be that someone bumped something they shouldn't have when the logic board was replaced. Therefore, everything needs to be carefully checked. All connections from the analog board to the CRT yoke need to be examined. I just can't imagine that a resistor would suddenly go bad after the logic board was pulled for a cap replacement. It is far to coincidental. No, something must have been bumped and either yanked out of place or broken to get your screen to flake out like that all-of-the-sudden.

 

[garyg42]

Thanks JDW for reply:

To simply my request for answer re focus problem, I didn't state full story.

My SE 30 motherboard failed in May, and I purchased a used replacement from "Nextstep Recycle" in Eugene Or. This worked till recently, so I had two defective motherboards. I bought two sets of tant cap replacements and paid professional tech to replace both motherboards. (He charged me an amazing low price of $20 (Cdn.)/board). I've also been using a different computer technician for many years, probably the only guy in Victoria BC who will touch an old computer. He pulled boards and replaced. Both worked fine except for focus. When I asked him how often he'd done this kind of work, he said it was probably over 1K times. Though nobody is infallible, it's not too likely that he caused problem. As both motherboards had same focus problem, it would seem problem is not on motherboard itself, UNLESS TANT CAPS THEMSELVES CHANGED SOMETHING - but then other people would have had same problem. I was delighted that Trag had seemed to answer problem (though his response was re a Mac plus), and was looking for confirmation. Now fix is not so certain. Any other comments by anyone?

Trag told me value of fixed resistor (1 M ohm), but does anyone know value of variable (focus) resistor?

However since focus was fine beforehand, logic (dictates?) that problem is not with either resistor.

Input appreciated.

Gary

 

[phreakout]

Gary,

Can you post a photo of the screen so we can make determine whether this is spot on to what Trag said? In the mean time, I'll verify this with my own SE/30, even if it's not suffering the same problem.

73s de Phreakout. :rambo:

 

[JDW]

You appear to be confirming what I had guessed before. Namely, that you did NOT have this screen focus problem when you first had your SE/30 operational, prior to any motherboard recapping jobs. Hence, I still feel confident that something was bumped or broken, either on the analog board and/or yoke which is causing your focusing problems. And yes, I too agree that a photo of your screen would be useful in this case to see the precise type of focusing problem you have.

But again, I have never had this kind of problem occur, neither before nor after a recap job. And keep in mind I have used electrolytic caps as well as tantalum caps on my logic board. The simply fact is that the logic board is also called the "digital board." Focusing is analog. If your digital motherboard is fried, you might not get any picture at all, or you might get some kind of oddball pixels, but you won't get an out of focus image due to a problem on the motherboard. Your troubleshooting "focus" needs to be on the analog parts in your SE/30.

 

[Osgeld]

unless that filter chip is flooding the system with noise, course if it were enough to cause focus issues on a totally different system its going to cause all sorts of havoc

 

[phreakout]

JDW is correct on what he has said. Most display issues are centralized around analog technology, hence the analog board. If it were a problem centralized with the logic board, you would have had additional artifacts (pixelation, etc.) associated with the main problem. The SE/30, and all compact Macs of that era for that matter, were only digital on the logic board. The remainder of the machine is analog, from the power supply to the CRT.

I would get some pics and post them here to verify the diagnosis of an analog board issue.

73s de Phreakout. :rambo:

 

[garyg42]

Dec. 31 /09 Almost New Years Eve:

Thank you all good folks who replied to my problem. Phreakout (Joe), I enjoy your postscripts. Here's one I just made up: (Hey Joe, where you goin' with that ram in your hand?).

To reiterate, only problem is focus. I've been asked to show an image of problem. Unfortunately I can't now. Gunnar, my technician, took SE 30 to his home after we discovered this problem, so don't have machine.

I didn't delve into any files, but after startup, desktop appeared and all names including all items in title bar were slightly out of focus, easy enough to read, but for me, unpleasant.

I don't mean to create a red herrings, clues suitable for Columbo, but when Gunnar did remove motherboard, and gave it to me, he pointed out that one cap was missing - he had somehow knocked it off removing board. (Thanks Columbo writers), maybe (though I find it hard to accept), Gunnar did create a problem.

Gunnar then told me that it was probably CRT that had become defective. When I questioned him he said it sometimes happens suddenly. I contacted forum because though I have great respect for Gunnar's experience, I don't believe it's a CRT problem.

There is no computer store in town that I can take it to - they won't touch an old machine. I've spent so much time and energy up to now. The crazy part is that I don't NEED machine. I can transfer all old info to my Mac G5, but the SE had a screen saver that fills me with joy when I see it, a tribute to my beloved dead cat: "I think I shall never see a poem as lovely as my cat, Suki." Why not just do the same on G5? Just prefer the way it was.

Best New Year wishes to all.

Gary Greenspoon (g2)

 

[JDW]

I have never had any caps "knocked off" when I have removed or inserted SE/30 logic boards. But I used to be a service tech for the now defunct MicroAge so I know how to exercise care. But what I can say is that capacitor was surely "ripped off" the board rather than simply "knocked off." As such, I would take a magnifying glass and examine the traces. For indeed, I can say with no small amount of certainty that at the very least the pads on that cap were also ripped off, but probably also some of the traces as well.

Despite all this though, the logic board would not have caused your focus problem. And I define "out of focus" as "being blurry" or "not sharp." If that is how you define it as well, then my previous advice stands. Check the CRT yoke board and all analog circuitry.

 

[tomlee59]

JDW is quite correct -- poor focus is not caused by a logic board problem (except, perhaps, indirectly by loading the power supply; that possibility is quickly checked by simply measuring voltages).

Check the board that holds the CRT socket. Perhaps some connections there came loose during the repair work. Reseat the socket. Inspect the pins and socket for corrosion, etc. and clean if necessary.

I don't recall if there is a focus control on the SE/30, but if there is, give it a tweak. The control may simply have some dirty contacts.

Check the connections to the flyback transformer. Freshen the solder joints if any look marginal (I generally freshen them as a matter of course). Don't just reheat them; use fresh solder.

 

[trag]

Hi Gary,

Did your tech check R26 to see if it is shorted or open? I ask because I've seen this exact problem on three or four Mac Pluses and Pina's recommendation to check the corresponding resistor on the Plus always solved it.

My only uncertainty is that "The Dead Mac Scrolls" is pretty old and in a later book "Mac Classic and SE Repair and Upgrade Secrets" he writes that there were as many as five versions of the SE & SE/30 analog board, so I don't know if they all used R26 (as stated in Dead Mac Scrolls) for the focus circuit. Unfortunately, he doesn't mention focus problems at all in "Mac Classic and SE Repair and Upgrade Secrets" but he is very definite about it in the SE (same analog circuitry as SE/30) in "The Dead Mac Scrolls".

Jeff Walther

 

[tomlee59]

By chance a friend dropped by with a broken SE today, giving me an excuse to open one up. There is indeed a focus control. Have you tried adjusting it? If it has no effect, then follow trag's advice and check R26. The focus circuitry is very simple, so finding and fixing the problem should not be too hard.

It is perhaps useful to note that a defective CRT can also exhibit poor focus, but this symptom is generally accompanied by other artifacts, such as severe ghosting, excessive brightness, or intensity saturation. It's rare, but not unheard of.

 

[garyg42]

As my first post said, I tried adjusting focus control - it did nothing. I will replace R26 as Trag told me: "R26 is a 1 M ohm, 1/2 watt 5% resistor on the analog board."

But is R26 the variable focus pot, or fixed resistor in series with focus pot?

If in series, does anyone know value of the variable focus pot?"

gary

 

[phreakout]

R26 is a fixed resistor, not a variable pot.

73s de Phreakout. :rambo:

 

[tomlee59]

Here are some additional notes:

The focus and cutoff controls share a common supply. If the cutoff adjustment has no effect, that supply voltage is the problem. If the cutoff adjustment works, and given that you have verified that the focus control has no effect, the problem is either a bad 1M resistor (the previously-mentioned R26), or a poor connection between the focus control wiper and the CRT focus electrode. Verify that there's continuity between the wiper and J2-9. Since the appearance of your problem coincided with a repair job, it is possible that the focus pin in J2 got dislodged or damaged. Inspect it carefully to verify that both mating surfaces are where they should be, and that they're clean.

There is also a 100k, 1/2-W resistor (R6), and a 0.01uF/1kV capacitor in the focus circuitry on the CRT board. If the resistor is open, or if the capacitor is a short, you will also have focus problems.

 

[garyg42]

Solution to my focus problem:

Thanks to all for input. Here's solution told me by my tech.:

The adjustment he was referring to is the cutoff. I have already done that - turned the cutoff down and turned the brightness up. I also cleaned both the focus and cutoff pots. It is a bit of a balancing act, but it has improved the focus about as good as will be possible; the focus adjustment is now quite apparent and there is even a tiny bit of headroom - there is a point in the adjustment where the clarity peaks, beyond which it again goes out of focus.