F100 issues

Just got an F100 in what appears to be fairly good, but obviously old condition. When it first arrived, I tested it out, and it seemed to work beautifully. Took it to it's first gig (mostly just to try it out in practice, I didn't really need it), and hooked it up. It heated up fine, but the pump wouldn't run.
Now, back in the shop, I measured the voltage on the pump leads, and it seems to be 110VAC, whether or not the run button is pressed (timer is turned off on the timer remote). I also measured with a scope, the input voltage to the pump optocoupler. You can see a train of pulses when you press the Run button.

So, to me this says that the problem is either the SCR, the pump, or the optocoupler.

With the power off, the resistance across the pump windings is high, but not open (about 1 Meg).

What should the resistance of the pump windings be? Is this indicative of a bad pump?

If this is the case, does anybody here have a surplus pump they wouldn't mind selling?

I haven't really worked much with SCRs but I seem to remember they require a load to work properly, so is this why the voltage is 110VAC? Is the pump not giving enough load to the SCR for it to work? Or is this a bad SCR?


Thanks,

Jeff
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    Barring a gate to main lead short in the SCR, on the first unit, I would suspect cap C5. If it should fail shorted, it could allow a lot more than normal gate current to flow in the SCR, and perhaps take out R17. I would think it would have effect on R16 as well, but if the SCR never conducted, perhaps not. Myself, that part of the circuit is so simple, and since you have already changed the parts with any $$$ involved, I would be inclined to just change the works - at about $.02 per resistor, and probably not more than $.10 for the caps, it's cheaper to "shoot the works" than to spend the time.

    Also, if you jump either across the opto, it looks like pins 4 and 6, on the second, any life? If not, then how about if you jump across the SCR, does the pump run? If the latter, then the SCR out is good, and you need to look at the SCR towards the opto. If jumping the opto works, then obviously it is either the opto, or the drive going into it.

    On the second unit, what do you see on the SCR gate when the run button is pressed? And by "R16, R17, and R18 *seem* fine", please define "seem" in this context - did you meter them, or are you just noting that they are unburned?

    - Tim
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  • 0
    Barring a gate to main lead short in the SCR, on the first unit, I would suspect cap C5. If it should fail shorted, it could allow a lot more than normal gate current to flow in the SCR, and perhaps take out R17. I would think it would have effect on R16 as well, but if the SCR never conducted, perhaps not. Myself, that part of the circuit is so simple, and since you have already changed the parts with any $$$ involved, I would be inclined to just change the works - at about $.02 per resistor, and probably not more than $.10 for the caps, it's cheaper to "shoot the works" than to spend the time.

    Also, if you jump either across the opto, it looks like pins 4 and 6, on the second, any life? If not, then how about if you jump across the SCR, does the pump run? If the latter, then the SCR out is good, and you need to look at the SCR towards the opto. If jumping the opto works, then obviously it is either the opto, or the drive going into it.

    On the second unit, what do you see on the SCR gate when the run button is pressed? And by "R16, R17, and R18 *seem* fine", please define "seem" in this context - did you meter them, or are you just noting that they are unburned?

    - Tim
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