Hi!
Long-time viewer of the channel and have come across the forums on my debugging travels over the years.
I bought one of those highly-regarded T-962 reflow ovens a few years ago, performed firmware, cold junction and kapton tape mods on it, and despite its shortcomings, it's more or less worked. Until now.
Temp suddenly isn't getting hot enough to reflow even Sn/Pb paste. Seems to be sensor-related. Wondering if you guys can suggest anything before I start throwing pennies at it.
•Think I can confirm, thanks to ohmmeter measurements and a temporary miswiring of the thermocouples (oops!), that triac, SSRs and quartz elements are all fine, as I managed to get the oven to be TOO hot, and blew up some caps. Good times. Back to too cold now.
•TCs both measure below 0.1mV at room temp, with 5-7 ohms across each. This is definitely wrong, no? Not an expert, but Google tells me it should be at least 0.8mV. My meter may be rubbish at such low voltages.
•Firmware reports a ~20 degrees difference between TCs (with Left being the clearly-wrong one).
•DS18B20 reads a sensible temperature.
•BOTH TCs failing seems unlikely to me, so I expect a common point of failure. Op-amp? Resistance measured in FB loop suggests op-amp gain on both channels SHOULD be around ~80, but one of the op-amp's output voltage doesn't reflect this. I'm never comfortable pointing straight at small-signal silicon as a point of failure! Would prefer to ask if op-amp failure is likely as I'll fork out for a better chip if that is the case, and £5+ is a lot of money in 2023 Britain. You could get at least half a biscuit for that.
•Can't really think of a particular event which may have caused it, besides setting a SAC305 profile to be slightly too high last week. Perhaps as a result of this failure creeping in, in hindsight.
Thanks for any guidance.