radio10 said:
I think the MAX406 is an op-amp.
I think the LT508 1298 might be a A-D converter but I can't find any info other than a vague reference. I was hoping this was an Opto.
There is a 93LC46 which I believe is a PROM.
Then there's the PIC16C57 28 pin device.
All seems potentially OK, ie display works, voltages appear as expected.
The fault seems to be the switching of the heating element which is locked ON all the time.
However I notice there is nothing happening and no change to MT1 on the triac during any state including forcing the temperature sensing.
I can see DC levels varying on the temp pot.
Says here the LT508 is a Power Factor and PWM control voltage device.
If you have a scope, probe the gate to common side and look for a
pulse. If you see a pulse there like it's trying to turn off the gate,
it is a good possibility the Triac could be bad.
If you can look at the triac number and see if it is a sensitive
type, these types are known to have issues and they could lock on..
what I have seen happen in some cases is this, if the power supply on
the control board bets a little noisy due to bad caps, a small ripple
can be present at the gate and thus turning it on..
If you are not sure about this, you can disconnect the gate and then
do a meter ohm check between the gate and one of the terminals.. A
non-sensitive gate type will have some resistance down in the 300 or
less range. Most of them are in below 100 ohms..
You many not have a opto isolator since the output voltage is most
likely low to start with. One of my stations only uses 6 volts if I
remember.. And a couple of others use 24 volts. Either way, the driving
electronics more than likely is directly coupled to the gate. This is
actually a bad idea btw. You happen to touch the tip some where in a hot
spot of a piece of equipment, it can back track and take out the
stations control electronics. The heater elements are suppose to be
isolated, but HV tends to jump over boundaries.
Jamie