Epson 4990 Photo - problems after cleaning inside of glass

I recently bought a used Perfection 4990 Photo scanner to make proofs from my 4x5 and 8x10 black and white negatives.

It's worked fine since I bought it, but I've been irritated by a layer of cloudiness and dust specks on the backside of the glass, both top and main unit.

I found a few guides online, pulled the lid and unit apart, cleaned the glass and reassembled. Everything seemed straightforward and relatively simple.

These are the two I used:

https://rangefinderforum.com/thread...elp-with-glass-platen-cleaning-needed.169734/

https://tinker.koraks.nl/photography/ghosted-when-and-how-to-clean-an-epson-4990-transparency-unit/

However on testing, the unit powers up with a green light that quickly turns to a rapidly flashing red. I've done a little debugging and it seems there is a problem with the lid, when I disconnect it the scanner lights up as green and works ok, but that won't help when I need to illuminate through a negative or slide.

Upon first inspection, I found that the lid light lock wouldn't go into the lock position, so I popped it open again, made sure the light carriage was at the end of it's travel so that the lock would fit correctly, and closed it back up. It worked for one scan, the results of which were bizarre. Obviously something is still wrong with the unit. Well, the lid lock once again won't move into the locked position, appearing that the light carriage in the lid won't move all the way to the final resting/starting position.

Now I get the fast-blinking red light every time I power it on. If I disconnect the lid, green light.

I've disassembled 3 times and checked, there aren't many ways to go wrong, it's all very simple in there. Carriage rides along a metal rod on one side and is loose/free on the other, and when all the way back in the rearmost position, the locking pin to keep the transport fixed works, but when I unlock it and try to use it, the red flashing light appears and the lamp carriage won't lock anymore, indicating it's not at the rearmost position.

Maybe it needs some kind of reset or position reset so that it knows where the lamp carriage is? The main unit lamp carriage needs to be manually moved in order to reassemble the part with the glass. The TPU appears to need the carriage all the way to the rear (parked) position, everything seems ok, but I still get the flashing red light.

Not sure what else could be causing this.

I was very cautious and gentle when I took it apart and reassembled it, but obviously something is not right, and I'm not sure what. I expect it must be something related to the light carriage in the lid, but everything appears to be seated correctly and in the right position.

Has anyone here any experience with these and might have an idea as to what could be wrong?

Thanks for any suggestions or ideas you can share.

I've not encountered this issue - otherwise I surely would have mentioned it on my blog!
The first thing that comes to mind is that an internal connector within the TPU has become dislodged.

By any chance, did you also clean the metal rod, which is part of the linear bearing? IME, this actually needs to be lubricated, but only a very small amount of grease is needed, so it it appears clean and dry (but should never be "squeaky clean"!). I put a small amount of light grease onto a clean rag, lightly coat the rod with the grease, then with the same rag, wipe away the excess. For my Perfection V700, I did this on both the lid and main scanner, and this eliminated random errors and lockups. And at least on the 700, if a toothed belt slips off, no worries, just pop it back into place, no specific location needed, as the mechanism is self-calibrating.

4season said:

And at least on the 700, if a toothed belt slips off

Click to expand...

Oh that's a good point; the transparency lid of the 4990 does have a very unfortunate tensioning system for the belt in the TPU. This connects with the lid on the front side of the scanner, but the plastic there can get weak / brittle and in my case it even broke off. However, I can't recall having seen any error lights - and I even didn't make it that far, since the attachment actually broke off when I wanted to make a scan (not during cleaning) and all the rattling and lack of any image data in the scan made it blatantly obvious something pretty serious was off. I made a provisional repair - and that still holds.