Have had similar issues with my prior unit – Standard Horizon model 150 which went out of production some 15 years ago and parts are hard to come by and only on flea bay.
What brand and model is your speedometer? No – no tubes per se. Yours is all electric. The paddle wheel has a small magnet in one of the blades. As it rotates, the electric pulse is picked up by the transducer creating an electrical pulse which is transmitted via the wire to your bulkhead gauge. The faster the wheel turns the pulse increases and your gauge registers greater speed. Vast majority of issues are caused by growth around the blades, the blade shaft or water facing of the transducer. Ensure this is absolutely clean and blades turn freely. Normally requires cleaning several times each season. If this is good, then your transducer may be worn out / faulty. Virtually all are made by Airmar and their web site has an excellent cross reference of your unit to their current part number. This will require re running the wire to your gauge which is often PITA and involves boat yoga. In my case this fixed the problem. When I had problem with other units of my instruments and parts were nowhere to be found, Santa was very nice and provided a new suite with all the latest whiz bang features Best of luck John and Maryann Legacy III 1982 C&C 34 Noank, CT From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of General Gao via CnC-List Sent: Sunday, April 12, 2020 9:18 PM To: cnc-list@cnc-list.com Cc: General Gao Subject: Stus-List speedometer - C&C 35 Mk2 My speedometer was not behaving well last season. I am planning to fix it myself. Googled the keyword, it came up a few documents suggesting blowing the tube to clear clog. I looked at my gauge and where there sensor is, I don't seem to find a tube there. Please see the pictures attached in the link. Could someone help me with the diagnostics? Thank you in advance. https://drive.google.com/open?id=1nYSpxnzb1BImby5jz3ASLnSD3OYxKT3P https://drive.google.com/open?id=1bBgw-Ln_wr2Qae-GUCk3L_I_dAQO-ekY
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