Scan Lines with Epson Perfection 1650

I got an Epson Perfection 1650 flatbed from a Deceased Camera Club member some years ago and used it successfully for years to scan negatives for Local Newspaper jobs. He made a Cardboard 'Mask' with the Cut-out area so it would scan Medium Format 6x6 negs with some 'Cut-off at the sides. With Vuescan Pro which 'won free' it found medium format well. Now I get 'scan lines' on Medium Format and 35mm and there is an 'internal break ',in the AC Adapter A291E near where it plugs into scanner port. I have to f'iddle' with the wire then suddenly it will 'Preview and Scan' BUT I get 'Scan LINES' driving me mad ! I HAVE taken off top and cleaned GLASS underneath with Micro-Fibre Cloth. Any Help ? ( Software I use is FastStone Image Viewer OR PhotoShop 7)
medium Format

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35mm

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This does not really look like scan lines, i.e. the spurious pattern is not just straight lines along the scan direction, but looks like a "cloth effect". I would suspect some sort of electronic noise/interference. Possibly from an ailing power supply.
Is your power supply external? If yes, is the brick heavy (transformer) or medium weight (switching)?
If the power supply is an external brick, can you look up the output voltage and current ratings? Can you substitute another one with same voltage and at least as large current rating, provided you can find one wit matching connector?
If you or someone near you has the necessary skills, could you connect a, say, 1000µF or more capacitor (of suitable voltage rating) across the wires between the brick and the scanner?
Completely different: try changing the USB cable. Following advice from Ed Hamrick, this solved an issue with my Epson V700.

+1 for post #2.
1. Fix or replace the power supply.
2. Clean and lube the rod the scan block travels on.
3. Inpect the drive belt for broken teeth and cracks.

Right !! There IS a problem with the Epson AC Adapter 291E with 24 v output. There must be an internal part break in the thin wire where it goes into the scanner-- I have to spend time 'wriggling' the lead then suddenly it will Preview and scan correctly. I have a replacement AC Adapter 291 E on order, should arrive Monday or Tuesday.

The wires comming from the transformer/power supply to the scanner are polarized, +,-. Its either a white lline down one wire or ribbed on one side. Two wires are molded together and insulated from each other. The molding on the plug can be cut with a razor knife and peeled back from the plug, the wires stripped at the end, the plug cleaned and the main wire soldered onto the plug. The plug can resealed with the molding and electrical tape or similar.
The transformwr/power supply can be cut open along its center seam, the halfs seperated, and the circuit repaired.
The power supply brick is a step down transformer, bridge rectifler, and filter to provide a smooth DC output voltge.
Disconnect the AC input before attempting to open, toss if the transformer is bad.
Replacement is the best route. (Tip for DIYers)