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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: Prime on February 08, 2009, 06:28:07 PM
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I have an A2500, it seems to work fine except for the mouse movements. The mouse buttons work fine, but the X, Y axis don't work at all. I read on NewTek's site that it could be a fuse, but I don't see a fuse (Small green soldered one that looks like a resistor.) I checked with an ohm meter from pins 5 and 9 all the way to the paula, which seems like a straight shot with no resistance. The only thing inline that I see is a ferrite bead. I guess the next thing I can check to see is, if the mouse port is receiving 5+. I already tried to replace the Paula and the CIA's.
Any Ideas?
Thanks,
Joe
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Look REAL close at your motherboard, just to the left of the mouse port IIRC. Might be smack dab in the middle of the two also. There is indeed a TINY ceramic cased .5 amp fuse. Typical for these to blow (never plug joys/mice into an Amiga when it's on!). I have a few if you discover you need one. Try "jumping" the fuse first maybe and see if the optic sensors spring to life on your mouse...
(http://www.coinopdreams.com/A2k.JPG)
Since this is a commonly failing part, I'd solder wires and a regular fuse holder to her - which is precisely what I did on mine. Haven't had to replace the fuse since, but will make it that much easier if/when it blows again.
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Forget PotX & PotY, they're the analogue inputs used for paddles and such. You need to check pin 7 for +5V. Check FB215 and especially F1 (possibly green, resistor-like) between keyboard and mouse port.
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I still don't see the fuse, so here is a picture.
I am going to test for 5v.
If there is no 5v on pin 7, what then?
(http://www.sccaners.org/a2500.jpg)
Joe
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If nothing of above helps, locate U74 and replace it (74HCT157), preferably wit a socket
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The fuse was added at Rev 6 motherboards. That looks like a 4.5. So, it could be a blown trace, if there's no 5v at the joystick port.
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Ahhh yes... the good 'ol mobo revisions. Shoulda thought of that, shoulda thought... LOL! Indeed his mobo does not look like my 6.2.
Before changing out that U74 chip though, I'd test all of those diodes and tantalum caps running about the ports. Tantalums fail QUITE often (especially after 15-20 years) and when they short, chances are they would take out something else in line - like U74 if it's on that particular mobo. FYI: you MAY replace tantalums with electrolytics to be on the right side of preventative maintenance.
And a blown trace could have happened because of battery acid leakage you're thinking JimS? Or sloppy techs dropping their screwdrivers on the mobo too I guess. lol
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save2600 wrote:
And a blown trace could have happened because of battery acid leakage you're thinking JimS? Or sloppy techs dropping their screwdrivers on the mobo too I guess. lol
Possible... but I was thinking more like the trace acted as a fuse and vaporized. I've seen it happen on some machines that came in for repair. That's why they added the fuse, both to the joystick ports and the external video port as well.
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Actually, there is 5v to pin 7.
I could change to electrolytic caps, what are the caps
rated at?
There is no U74 that I can find anywhere on this mobo.
Figures, it couldn't be something simple!
Joe
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Sometimes it really *IS* the simple stuff... do you have another mouse to test? There are components and an I.C. inside the mouse that can fail (unlikely, but I have run across "dead" mice). Are the female pins okay? Not completely recessed causing lack of good contact from some oaf clumsily inserting it in and out? lol
Before mucking up your mobo, do you know how to check those caps? Use your DMM and make sure they are not the culprit. Look for a reading of (going by memory here) .1-.4 on the diode test (not continuity) function of your DMM. Basically, measure both sides of each capacitor and look for a shorted or way out of spec cap compared to the others. That'll be your culprit. Same with testing the diodes. Reverse the leads though for them. + to - will read .4-.5 (or whatever the consensus is), but when reversed, your DMM should test open. When reversing the leads and the DMM shows anything other than an opposite effect (ie: small current from the DMM itself OR no current the other way) - you've got a bad diode.
Not sure where else that 74HCT157 could be, should be close to the ports though I'd imagine. Still, check the caps and diodes first before attempting to replace an IC - for which you really should be using a logic probe for anyway. You know... hi-lo, pulse - that sort of thing.
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How can you test caps and diodes when they are mounted on a mobo? Doesn't this give bogus results?
Joe
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Measuring resistance - yes, of course. But you're not going through loops, coils and resistors here (or entire circuits). We're talking about different components: Capacitors and Diodes, which test differently. I never said to put your DMM in ohms (resistance) mode. Rather... you'll want to test in 'diode' mode. If components always needed to be removed from their respective circuits, the electronics service man would have completely and utterly died a LOOOOOONG time ago ;-)
Now... what are you waiting for? Break out that DMM and get to work or send your board to me!! lol
BTW: do you not have another mouse?!?
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Yes- I have tried other mice...
I love this stuff, so any little gems you can throw my way, be my guest!
I will check it tonight when I get home from work.
I am excited, hopefully we can get this bad boy working.
Joe
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In the little gems department, I once saw a 2000 where the mouse failed every time I tightened down the screw next to mouseport. Never did figure that one out... finally just put a plastic washer under the screwhead.
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@ JimS:
ROTFLMAO! Maybe you had an Amiga 2000 'especial' where someone from South America douched down the mobo with WD-40 ;-) LOL!
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Not me! I never used WD40 or a-likes near an Amiga! Can you name the stoopid? :inquisitive:
Here I have a totally destroyed A4000 (not by me!) were the guy had a battery leakage and he try "fix" it with iron wool !!!!!!!!!! :whack: :furious:
Now the board is on my hands, but not much to do with the "corpse". :headwall:
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Steel wool?!? Okay... but traces can be repaired. I've soldered wire the thickness of hair back in place. That's what needs to happen in your case. If your board is so shot to where you can't see where traces are supposed to go, get a close up pic of the board and go from there! Nothing to lose since the board is already toast. Still... can't imagine *that* much leakage ruining an entire block of traces you can't "trace"... unless the guy was very liberal in his application of the steel wool! LOL!
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He was...
The leakage covered all the SIMM sockets, RTC, mouse and game ports.
I don't know what else he did, but simply there are no traces any more.
OK, I'll stop thread hijacking. ;-)
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>The leakage covered all the SIMM sockets, RTC, mouse and game ports.
>I don't know what else he did, but simply there are no traces any more.
Perhaps, it's possible to minimize the repair work with an add-in board or CPU card. Use Mouse from some serial board, memory from some CPU card or memory board and forget about the RTC.
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>by JimS on 2009/2/8 21:43:10
>>save2600 wrote:
And a blown trace could have happened because of battery acid leakage you're thinking JimS? Or sloppy techs dropping their screwdrivers on the mobo too I guess. lol
>Possible... but I was thinking more like the trace acted as a fuse and vaporized. I've seen it happen on some machines that came in for repair. That's why they added the fuse, both to the joystick ports and the external video port as well.
I think I vaporized something on my A500 long time ago by pluggin in a Mimetics genlock into the computer while Amiga was on. The genlock died instantly but Amiga 500 still works great but it no longer works with A520. The monochrome video out still works. Any picture of where that fuse is on video port on A500?
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amigaksi wrote:
I think I vaporized something on my A500 long time ago by pluggin in a Mimetics genlock into the computer while Amiga was on. The genlock died instantly but Amiga 500 still works great but it no longer works with A520. The monochrome video out still works. Any picture of where that fuse is on video port on A500?
I don't see any fuses on the 500 schematics. But it does sound like you've fried a trace. Check pins 21 (-12v), 22 (12v), and 23 (5v). If you can't see the open trace, you can use 30ga wire to tap the proper voltage from somewhere else on the board. I'd consider soldering in one of those fuses just in case.
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save2600 wrote:
ROTFLMAO! Maybe you had an Amiga 2000 'especial' where someone from South America douched down the mobo with WD-40 ;-) LOL!
Well... I don't know about that... at least it wasn't duct tape. ;-)
But I have seen a few strange failures. Like a bad CIA missing one bit to the printer port. So every time a character with that bit on printed, it came out wrong... but other characters printed fine. Or my own 1000 that had a stuck RTC in it's CIA chip. The system time would run for about 10 seconds then jump back groundhog day style and restart. Kinda useful for hack lite that was seeded off the RTC. There were only a few starting positions, and once you memorized them.... ;-)
I once had a similar problem on the mainframe I used to repair. It's backup RTC counter was broken and was basically running at about 4 times real time. We had to switch to the backup for other problems and nobody noticed the glitch until the system's clock thought it was the next day. They decided to stop all work until the world caught up with the computer. ;-)
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Well this thread kind of went a weird direction, but a perfect segway for a couple of questions:
I have an A3000 I just got, the mobo is in pristine condition and the battery was just starting to leak. I removed the battery and directly under the negative side there is a small place where the green solder mask chipped away to reveal copper. (A very tiny bit.) Should I drop some RTV on there, tin it or leave it alone?
And what is the "preferred" method of making sure any acid crystals get off the mobo? I have been spraying the area with flux cleaner.
Thanks,
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It should be fine if you tin it.