A few months ago, I bought an InFocus video projector on eBay, still hoping to watch movies on the wall of the family room. It’s about 1/12 the size of the behemoth Sony projector I was trying to repair earlier, and quite a bit sharper and brighter; so if I can get it going, it’ll be a nice replacement.
When I received it, I immediately noted two problems: It shuts itself off after anywhere from seconds to hours; and it has a yellow silhouette running up the middle of the picture, kind of like the face/vase illusion.
I’ve taken some time this afternoon to disassemble and diagnose the projector; so although it’s not fixed yet, here’s what I know so far.
Chasing the Yellow Blob
In which Keith removes Crusty Gummy and washes a filter carrier
From the looks of it, I was pretty sure that the blob was going to be something wrong with, or wrong on the surface of, one of the lenses, mirrors, or filters. Yes, it looked a little like an LCD ruined by being left in a freezing car overnight, but not quite. So I dug in to follow the light path through the projector and see if it would be apparent what was wrong.
After popping the cover and removing the main circuit board, I could see most of the periscope-like light enclosure. I removed a couple of lenses that dropped in from above, which were clean, and looked at a couple of mirrors, which were also clean. The next thing I wanted to check was the LCDs.
In order to get to them, I had to take off the collar above/around them, remove the two cooling fan / speaker assemblies, and remove the main lens. The LCDs were mounted to the lens carrier and looked fine; their removal left access to this cavity where the RGB light paths converge.
I didn’t notice it until later, but someone had already been here before. Loctite on the RG screw tabs and missing from the B tab.
From a different angle, the problem was obvious.
The filter between the blue light path and the blue LCD is all melty. Bad.
First things first. I gently peeled off the Bad, scrubbed all the goo off the glass carrier with Goo Gone, washed all the Goo Gone off with Dawn, rinsed the Dawn off with water, and dried the water off with a paper towel. (Life is sooooo complicated.)
Here it is all shiny and ready for . . . whatever comes next.
While I was in there, I detached and examined the other two filters. They didn’t look colored, just a light neutral grey in a very familiar sort of way. Apparently the filter isn’t what makes the blue blue (that’s the blue half-mirror further upstream), so maybe I can just put it back together and see what happens.
Reinstalling the Filter Carrier
Assembly is the reverse of disassembly.
The projector is back together and emitting blue light when it should be emitting black. The Bad was the polarizing filter that makes the LCD do its thing, so I’m going to have to find another one and put it back. It’s still emitting shades of blue; it just puts out quite a bit of blue when it should be going all the way to black.
I’d welcome donation of a spare polarizing filter from a differently-ruined LP290, and I’m shopping for a broken one. But partly for sheer “I can’t believe you did that and I can’t believe you got it to work” value, I’m sorely tempted to get a polarizing filter somewhere else and see whether it’ll do the job. Like a photographic filter. Or an LCD from dead equipment. Or sunglasses. 
Of course, none of those are good ideas. It obviously gets hot inside the projector, and meltage problems are going to avalanche as the filter warps and discolors and becomes less transparent and absorbs more energy from the light and heats up and warps and discolors. So I’ll at least look around for a spare projector to cannibalize.
Power Supplies
The projector has the lamp cover interlock switch and AC-DC power supply on the starboard side and the DC-DC power supply and lamp ballast on the port side. The AC-DC supply is always on, and the DC-DC supply appears to be under control of the microprocessor that runs the soft power button and monitors the sensors scattered throughout the projector.
The AC-DC power supply checks out okay, as far as I can tell. All of the electrolytics test good with my Capacitor Wizard, and the three voltages (16.5V, 6.6V, and 3.3V) are present on the edge connector that plugs into the main board.
I took the projector parts over to Ron Tozier, and he suggested testing all the voltages with the projector in standby, with the projector on, and after the projector shuts itself off. That should help determine whether the failure is in the AC-DC power supply board (probably not), in the DC-DC board, or quite possibly with one of the sensors. He also noticed that the main board has nicely labelled test points for lots of voltages, including not only the raw AC-DC supply outputs but also regulated and switched voltages under microprocessor control.
I printed out a digital pic of the main board, highlighted all the power supply test points and wrote the standby and on voltages next to them, and am now waiting for the projector to shut itself off. Of course it would pick now to stay on for hours.
I do note that every time I turn it on, as it powers up the lamp, I hear a chittering sound like an ultra-high-pitched buzzing. I think it’s the ballast going out, and I’m pretty sure the projector would sense a ballast failure and shut itself down. So I suspect I have a pretty good idea what I’m going to find is causing that problem as well.
You can purchase bulk sheets of polarizer from places like Edmund Scientific. The stuff isn’t exactly cheap, but a sheet will give you plenty to do the repair with and quite a bit more to play with.
Oh, just make sure you get the linear polarizing sheets, not a circular polarizing sheet (which are good for making antireflection devices, since the sense of the polarization is reversed when light specularly reflects).
The temperature is a concern, though. All of the polarizing materials I’ve ever seen have been plastic based, and I’m not sure at what temperature the plastic may melt.
Speaking of temperature, quite a few projectors include a dichroic mirror in the optical path to reflect infrared (heat), and only let visible light through. You might check to see that such a mirror/lens hasn’t been
removed. Then, again, with the existing coloured beams, that may be taking the place of the dichroic mirror.
Dave
polarizer can also be removed from old lcd products (T1-82 calculator should be sufficient for your purposes)
the high frequency buzzing, might be a failing electrolytic cap.
-Dane
awesome site by the way!
I too have an LP290, It’s not completely broken, so I can’t sell you the polarizing filter, Sorry! However, I am having some strange power/shutdown issues.
Most of the time (95%) after being unplugged for extended periods of time (5-15 minutes), the projector will power right up, and work for hours. I say 95% because recently, it will power up, begin projecting the signal it’s being fed, and within 30 seconds, display multicolored garbage completely unrelated to the VGA input signal, and shut down.
However, (this is the reason I got this projector from a friend for free) after shutting it down, either normally or after one of those new & odd ‘crashes’, it will often times refuse to power back up unless I unplug it from the wall, and give it time for it’s capacitors to drain (5-15 minutes). It will make the two normal pop click noises from the speakers, (I assume from the mini amplifier powering up), fans begin whirring, beep the normal power up beep, and then unexpectedly shut down as if I yanked out the power cord within the following second.
I would love to see what you find out is wrong with your projector’s shutdown issues! Keep us updated! (Nice pictures, btw!)
Bitcore, it’s tough taking pictures of black plastic; and my Nikon preview screen, iBook, Dell workstation running Linux, and PowerMac with Dell monitors all disagree about the proper brightness and contrast. :-/ I’m glad you like them.
Ron Tozier, my friend who’s an extremely knowledgeable TV and electronics repairman, suggested that the problem may be with one of the sensors, and it’s the microprocessor that’s shutting off the projector. I can’t get mine to break now!, so I can’t test that theory.
If you’re game for measuring some voltages inside your projector when it’s misbehaving, I’d like to send you a copy of my notes about normal test-point voltages and let you compare to what you see after shutdown. It’s not necessarily a direct route to a diagnosis, but it’s the next step.
I was hoping to update firmware v1.26 to see if it would resolve this issue (projector powering off – cooling fan not working properly). I was not able to… Has anyone tried this ? Any result ?
Chantalbiz, I didn’t even know there was a firmware that could be upgraded; so no, I haven’t tried it. Come back and let me know if it helps?
I face the exact same problems, the projector shuts off after a while. However I do have firmware v1.26… Solutions and hints very welcome…
Hi! I also have a LP290 i got for free. The lamp was old (2600h) but i found a new one very cheap. 60$. Original. Mine already has the 1.26 firmware but after a while i shows a blue line on the left of the picture. I have also seen this line att the bottom of movies where the black bar begins. It gets worse when the projector has been on for a while.
But I havn’t had any power problem yet. Only tested it for a short while.
> I’m sorely tempted to get a polarizing filter somewhere else and see whether it’ll do the job. Like a photographic filter. Or an LCD from dead equipment. Or sunglasses.
I’ve got Sony VPL-PX15 open on the kitchen table right now. Thinking along those same lines, I fabricated a new polarizer for the blue path from an old LCD display.
The main problem with this approach seems to be that the common polarizing filters just don’t seem to work as well for blue wavelengths as the original one.
This throws the color way off. I may be able to compensate for this for some video sources. I could also perhaps block some of the light to the red/green LCDs, (perhaps replacing all the polarizers with equally-bad ones). I’m willing to take some loss in output specs, considering how little I paid for this thing at a yard sale.
I’m also concerned that the reduced transmittence of the my replacement polarizer is going to cause it to melt down even faster.
Wondering if the original polarizer is something like the VIS 500 BC3 :
http://www.codixx.de/polarizer.html
I’m going to visit a camera store and see if they have anything that might be useful.
Like your blog!
It is as I feared, a photography polarizer burns out quickly in this application.
Have you found the polarizer for your projector? I need one for a LCD projection TV.
Brent, yes, I pulled polarizers from a dead, different projector and hacked it into my LP290. It seems to work okay, although I haven’t closed it up and heat-tested it yet.
I tried to use the polarizers out of a dead projector but the dimensions didn’t match…. I needed 27mm x 21mm.. Oh! well.
If the dimensions aren’t too far off, you may be able to adapt the one you have.
If it’s too big, you can cut it down with a small diamond abrasive wheel. Practice on something else first, make sure you have the correct orientation, etc.
If it’s too small, you may be able to make a holder adapter. The polarizer before the LCD element doesn’t seem too critical in its placement (not like a focusing lens). I had some success making an adapter from soda can aluminum.
Hi all,
I plugged in my LP290 a while back, only to hear a loud crackling noise, some white smoke, and then nothing. I mean nothing. The toy will not power on anymore!!!! Any ideas?
Regards
JP
JP, I don’t know anything about projector repair other than what I’ve been able to figure out about the optical path using my own two eyes.
However, if you actually saw smoke, and if you have some experience with component-level electronics repair, it should be pretty easy to open the case, examine the area that the smoke came from, and find one or more components that are visibly damaged. At a minimum you’ll need to replace them, and quite possibly they burned out because something else in the vicinity is faulty.
Off the top of my head, I’d say this has maybe a 20% chance of success, which is better than 0% and worse than taking it to an authorized repair center (if there even is such a thing).
Sorry I can’t be more help, but you may note that all of the work I’ve really done on my projector so far is physical, not electronic.
First off, great blog!
I have an LP280 that I am trying to repair and I have pretty much taken all of it apart and cleaned almost every inch of it. I haven’t found any thing that sticks out that would cause any problems. But, I have a gigantic blue blob that shows up when the projector is displaying blacks and then a yellow blob when the projector is showing whites.
Here are a couple of images that show the problem.
http://www.need-name.com/blog/wp-content/uploads/2008/06/yellow_on_white.jpg
http://www.need-name.com/blog/wp-content/uploads/2008/06/blue_on_black.jpg
I am wondering if you have seen this before and if you had any suggestions…
Again, great blog and thanks!
Scott, this sounds exactly like the problem I described in this posting. Have another look at the pictures above on where to find the filters and double-check them, especially the one in the blue light path.
Regarding repair, you’re probably going to have to find somewhere you can salvage a replacement filter from another projector. Another reader has experimented with different types of replacement filters, and they all seem to melt except ones from other projectors.
I have an LP240 that won’t power up. I opened it and there are two vacant holes on the board on each side of the power switch. I think something is missing here. Can anyone assist an relative electronic neophyte here. The (perhaps) missing part would interface between the button pad and the board beneath it. Also, can I bypass the power on button by buying a remote for the unit? Thanks for any assistance.
Robert, do you have any pics of that online somewhere?
Is this a projector that you’ve had that broke, or did you acquire it broken? How much do you know about how/when it stopped working?
If the only thing wrong is the power button, it seems like you should be able to power it on with a remote, but I’m suspicious that there may be more going on.
Robert replied:
Thank you for your input. I just bought it at a school auction, so I am suspect of the way it was used. Like I said, it looks like there a piece that may have gone in the holes between the button pad (which goes through the top) and the board, but I’m not sure and cannot find a picture to help verify this. You’re right…there may be more to this. Would you recommend putting money into it (repair or remote purchase). Can I program a universal remote to turn on the projector? Any ideas are appreciated.
robert
Robert, have you posted any pictures of your projector where you think a part is missing?
My experience with non-working projectors is that it’s impossible to find replacement parts, it’s impossible to find documentation, and there are so many different models of projectors with minor variations that it’s essentially impossible to find dead projectors to cannibalize.
You could try a remote, but my guess is that the projector was broken, someone opened it to see whether there was anything obviously wrong, and they didn’t bother to put it all back together since it didn’t work anyway. So you probably have a root problem that was enough to break the projector, and now maybe missing pieces as well.
Sorry for the bad news, but I’ve been through this myself a few times already.
I have an LP280 that I am trying to fix. After you turn it on it shuts off randomly within a few minutes. I took the case off and made sure everything was clean. I can run the projector fine with the case off so I figured its a heat issue. I want to update to the lastest firmware which fixes a heating issue but i cant find the cables to do it. Anyone know where to look?
The cable has a rs-232 plug from pc to a mouse plug on the projector. The port is labeled mouse on the projector but a ps/2 mouse plug wont fit, it also has 8 pins which ps/2 only has 6.
I looked into the cable and found apple makes the same type. Its an miniDin 8 pin male to rs232 female cable. I ordered one and will post whether it fixes the random shutting off issue if you update the firmware to 1.26.
Brian:
Have you considered running with the case off, adding your own fans, etc?
I suspect that the designers push the limits to get everything into the smallest case possible.
It may be aging increasing heat, decreasing ventilation that’s tripping a temp sensor, the firmware update may support this theory. So you might be able to extend its life if you can live with a little bulkier enclosure.
Otherwise you can test individual components with “freeze spray”.
You can get a can of “component cooler” at any electronics supply (e.g. Radio Shack) or use a can of computer duster upside-down. (I think the only difference is the length of tube inside the can.)
Spray a few drops of the liquid cooler on various power transistors, ICs etc as the unit is warming up. You might find that cooling on a specific component fixes the problem, usually replacing this component fixes the problem.
Be a bit conservative with the spray, some parts or connections could be damaged by it. Usually a little on each power semi (anything with a heatsink) is all that’s going to be useful.
My experience has been about 75% success with this method for heat-related problems. It will usually find the degraded or intermittent transistor (whether or not that that’s the real problem).
- Marsh
Thanks for the reply.
The problem with the freeze spray is the unit runs fine with no case. So I wont be able to spray anything with the case on to figure out whats overheating.
If the update doesnt work ill try new fans or leaving the case open…
I have an Lp280 that I bought from ebay a couple of months ago
It runs fine no serious problems with it, other than the color will change at random, but that hardly happens.
My real problem is, is that yesterday the power tripped in our apartment while the projector was running. Once the power came back and I went to turn the projector back on it would make a ticking sound for a second or two and you can hear the fan run, but no light will come out from the projector. While all this is happening the power light will be blinking green.
any idea whats wrong?
much appreciated
John, have you tried again since then? My first thought is that when the power tripped, the fan didn’t stay on to cool the bulb properly, and the projector probably won’t turn on when it’s too hot inside. You’d think it’d at least turn the fan back on, but there’s no telling exactly how it was programmed.
If it still doesn’t come on, it does make me wonder whether anything near the bulb was damaged by the bulb slowly cooking the inside of the projector as it cooled without fan assistance.
Have you opened it up yet to look inside?
Whatever you do, don’t open the light path. All of the optics (lenses, mirrors, and filters) are factory-aligned, and I’ve not found any way to realign them if you loosen the screws. It may be possible, but I think it’s not going to be easy unless you’re a pro at it.
Well, today my roommates and I figured it was pretty much done for so we decided to take apart the projector. Well, we couldn’t take it fully apart without ripping it to pieces, so I decided to put it back together and gave it another shot by turning it on(we tried putting it back on many time before, but the light never came out) anyways, when I went to put it back on, by divine intervention…….IT WORKED!!!
I don’t know what I did, but it works now
it’s been interesting reading about the various ways these beasts can die and be revived. i’ve got an infocus screenplay 5000 that we got new (ouch) and only used it for about 10 movies before it did the following:
after plugging in, and powering up, no light, no image, nothing.
seemed like the lamp may have crapped out hundreds if not thousands of hours before it should have, but local internet repair person (who outsourced the job) says he can’t replace the lamp, but the ballast unit was the problem. $206 fix, but projector still won’t light up. aren’t the odds of a bad ballast and a bad lamp happening at the same time pretty slim? feeling like i’m being taken for a ride. any thoughts?
Nathan, I’m no expert, but I agree it doesn’t seem likely to be the ballast and lamp at the same time. Also the lamp is readily available for < $200 online, so I think your repair person didn’t know what he was doing and didn’t want to be stuck with a ~$200 lamp if that didn’t fix it. By claiming it was the ballast, he stuck you with the bill.
Pull the lamp (wearing gloves if you have to touch any of the glass so you don’t get oil on it) and look closely to see whether it has a filament. I don’t know whether it will or not; but if it does, measure its resistance through the lamp’s plug. (If you don’t have a multimeter, go buy one for $3 at Ace Hardware or Harbor Freight — the cheapie will be good enough for this.)
If there really is a filament and you get infinite resistance, the filament is burned out. If you don’t, the filament is intact and you should at least get light out of it — suggesting it’s a different problem.
Ron, my local TV genius, says projectors are nearly irreparable because the manufacturers won’t sell replacement parts and every model uses all different parts, so it’s next to impossible to find one to cannibalize or even swap parts for diagnosis. So I really don’t know what to suggest after this.
I have an Infocus LP290. It will power up, run fine for about a minute then shut off. I have read the previous posts and seems like I may have to install some heating issue update (it does smell a little like its overheating really quickly)… only problem is: most of what I have read sounds like greek. I am a quick learner and the projector was given to me by my brother, so if I can try to fix it myself I can at least learn something even if I dont fix it. The replies from Brian seemed to be going in the right way, but he never posted whether it fixed the problem or not.
What is the update to install and where can I find it? what tools will I need?
NewLearner, I have no idea — I don’t know anything about the update myself.
If Brian doesn’t respond in a few days, remind me and I’ll email him to see if he can come back and tell us what his results were.
For what it’s worth, I have a LP290 that behaves in exactly the way Bitcore described on January 23rd. Most frustrating.
I was wondering about the suggestion of measuring resistance of the bulb filament. I think that projector of that vintage uses UHP (ultra high pressure) bulb with a spark gap that ignites at high voltage as a starting mode, then when the gas ionized the high voltage drops out leaving a sustaining voltage to keep the lamp burning. Thus, measuring filament voltage suggestion doesn’t make sense since the gap would essentially showing open circuit, IMHO.
Hey, I have a LP280 and I have been trying to get the firmware upgraded, right now its 1.17 so im hoping the 1.26 fixes the problem(the picture turns red then shuts down) but no matter what I do I cant get the firmware to go on with the 8 pin to RS-232..at the step where you are supposed to hold the menu button then plug in the projector then release and hit the menu button again, its supposed to start. Ive looked at the settings for the com port and they are good…anyone have that issue?
Is it possible to flash the LP290 via USB Port not RS-232 ?
Same problem like Dillon see above
If i connect the USB Cabel Windows will see the new USB Device but it will not find or install the driver .
I have found this driver :pxprjusb.inf from Proxima
[Version]
signature=”$CHICAGO$”
Class=USB
ClassGUID={36FC9E60-C465-11CF-8056-444553540000}
Provider=%MFGNAME%
DriverVer=06/30/2000,0.00.0080.0
[Manufacturer]
%MFGNAME%=DeviceList
[DestinationDirs]
DefaultDestDir=10,System32\Drivers
[SourceDisksFiles]
pxprjusb.sys=1
[SourceDisksNames]
1=%INSTDISK%,,,
[DeviceList]
%DESCRIPTION%=DriverInstall,USB\VID_066C&PID_F1A5
;——————————————————————————
; Windows 2000 Sections
;——————————————————————————
[DriverInstall.NT]
CopyFiles=DriverCopyFiles
[DriverCopyFiles]
pxprjusb.sys,,,2
[DriverInstall.NT.Services]
AddService=pxprjusb,2,DriverService
[DriverService]
ServiceType=1
StartType=3
ErrorControl=1
ServiceBinary=%10%\system32\drivers\pxprjusb.sys
;[DriverInstall.nt.hw]
;AddReg=DriverHwAddReg
;——————————————————————————
; Windows 98 Sections
;——————————————————————————
[DriverInstall]
AddReg=DriverAddReg
CopyFiles=DriverCopyFiles
[DriverAddReg]
HKR,,DevLoader,,*ntkern
HKR,,NTMPDriver,,”pxprjusb.sys”
[DriverInstall.hw]
AddReg=DriverHwAddReg
;——————————————————————————
; String Definitions
;——————————————————————————
[Strings]
MFGNAME=”Proxima ASA, Norway”
INSTDISK=”Proxima Projector Manager installation disk”
DESCRIPTION=”Proxima Projector Manager”
Some guy told me I can use it is he right ?
greez diver
I’ve got the LP280 version, 3 of them to be exact. However 2 of them have the auto shut off after 30 seconds. I dont think this will solve everybody’s shut down prob but what i’ve found is the ground wire was not connected to anything, fact it was flopping around and I think it might have been making contact and cause a short. Since i’ve fixed the ground wire, the projector has been running fine. I’m going to tear the second one apart and see if it is grounded as well.
I have 2 lp280′s…but I cannot figure out how to open up the case! I loosen all visible screws but something on the right side (as you look down on the top) is holding it together. Is there something I am missing or do I need to just pull things apart harder? I don’t want to break anything…
I figured it out…it’s apart now.
In fact, I replaced the blue polarizing filter and now the picture is without the yellow blob. But there is a little yellow shadow to every thing. I think something needs adjustment…
Dave, glad you got it open! I hadn’t had a chance to check mine yet. What did you have to do to get the right side unstuck?
By “yellow shadow,” do you mean just a little fringe to one side of objects or the other, or do you mean the whole screen is tinted yellow? If it’s just a fringe, I wonder if your blue LCD is slightly out of alignment.
Dumb me, it was the audio in jack that needed to be released from the outside. That was it, but I guess I thought that the whole cable input section would be attached to the top case.
The yellow shadow is a little fringe in the upper right quarter of every image. I just now tried to adjust the blue polarizer thinking that was the culprit but it makes no difference when I move it side to side. How do I adjust the blue LCD? This is the blue side “pickup” screen on the lens assembly facing the blue polarizer, right?
Dave
hello
the fan of lp280 stop in discontinuous manner and sreen is green if warm
I’m sorry I’m french
thank you
I have gotten rid of 98% of the yellow shadow, but I am not terribly happy with the overall picture resolution. The whole image is kind of lacking in color depth but maybe I am expecting too much from a couple of old used projectors!
I’m new to repairing electronics, but I have repaired several LCD’s and a couple projectors.
My Infocus LP280 was overheating and shutting off anywhere from a few minutes, to over an hour.
When it did this, I would have to unplug the power from the back and plug it back in.
One other Infocus Projector at my work wouldn’t even turn on at all, so I did some research… And it was one of the capacitors that was by a transistor (Transistors get hot), and was only rated at 85 degree celsius.
I replaced the bad one with a high temp 105 degree cap, and it works great.
Ok, back to the LP280.
I took it apart and nothing looked bad/burnt.
I went ahead and replaced the 6 capacitors that were on the power board (I’m assuming that the LP290 looks the same), with good caps and it has been running for a couple hours without any problems.
This isn’t a confirmed fix, but it has lasted longer than it ever did, and hasn’t shut off yet!
The 6 caps that I replaced are :
2x – 1000uf 10v
3x – 470uf 16v
1x – 470uf 25v
You should be able to get these at your local Radio Shack, or online at http://www.parts-express.com.
Anyways, sorry to hijack the blog… Thanks for all of the helpful info!
If you have any questions or need pics, email me at zacharysides@hotmail.com
The above solution worked for me, I have used it almost everyday since replacing the 6x Caps and it hasn’t shut off even once.
Hope this helps somebody else!
Hi,
I’m glad to find this site – interest and help for lp290 owners! Great. I’ve had my projector since about 2002 and it has been a joy. I’ve seen hundreds of movies – learned a lot about film. Last summer I finally bought a new bulb – the old one had it – there were color problems too but I thought they were there because of the weakened bulb. The color problems did not go away with the new bulb – from time time to time screen color would get very red pink – or faces go grey and then return to normal for a while.
I had the projector hooked up via a SVHS cable – I wiggled the cable connector inserted in to the lp290 and noticed that the color problem could be effected by this. I then hooked the dvd player up via the RCA video cable/input which was a little better. But this too would they eventually go bad for a while – and then return to normal – and then go bad for awhile again – oh boy.
Does anyone have any experience with this problem?
I don’t want a new projector – I feel like there’s still life in the old friend.
Thanks,
Nick
Nick, it certainly sounds like you have a bad input jack or a bad connection from the input board to the rest of the machine.
Have you opened the case? I’d have a look at the connector from the input board to the motherboard. I don’t remember exactly what kind it is — a card edge connector, flex-pc, or ribbon. In any case, I’d check the interconnect(s), reseat it/them, and see whether that helps.
If not, I’d have another look at the jacks on the back of the machine — clean and/or replace them.
Hope this helps! Let us know how it turns out.
ZPack, that’s great news! Seems like a good idea to replace the caps anyway, and I’m glad to hear it’s holding up!