Hello-

I received a donated 1985 Sundance 501 (Balboa 2500 PCB Rev 4) that I just got running yesterday. At first, the tub would heat just to 98 degrees (even with the temperature dial all the way up), but all else worked fine including jets and blower (jets button took a push or two to start, though). The tub would maintain the 98 degrees, turning on and off as needed. I just figured that it needed a new temp sensor (residing in the skimmer).

Well, this morning the tub was up to 104 degrees and would not respond to the dial being turned down, just kept running constantly on low speed with heater on. Bizzarely, NOW the topside controls (air and jets) do not function at all. I thought the jets and air would work fine in it's constant low speed mode, even with a faulty sensor. I could replace the sensor ($40) and see if that fixes the shut off problem and restores the topside controls, but I would hate to spend the money only to find out the circuit board and/or topside are also faulty.

Relays are not stuck or burned. Temp Potentiometer reads from 0 to 1K Ohms on ohmmeter, so I guess that's OK as it says 1K printed on it. Disconnecting sensor has no effect. Disconnecting topside has no effect. Using a voltmeter on the temp sensor leads coming from the pack reads about 2v on 50v scale. Turning the voltmeter to 25v scale and taking a reading on the same leads does turn the spa off (while the spa was off in this state, I tried to run jets and blower, no luck). I DO get some microvoltage from the topside control "buttons" (barely registers a blip on the 500u scale). Anything else I should check before replacing sensor and possibly circuit board and topside controls? Thanks!!!