A couple of emulator problems

So I have a couple of new problems with my increasing herd of emus.

First, one of my older emus started behaving strangely lately. It starts up and begins to run perfectly, but after it has been on awhile, it decides that it needs to re-strike the lamp... even though the lamp is already struck, and burning perfectly. I've poked around a bit but was wondering if anybody has seen this before. I've tried 2 different logic boards, and multiple lamps (that all work perfectly in other fixtures), but it always behaves the same. Makes me think is a Power Supply or wiring issue. It, of course has no luck striking an already struck lamp, so after it has tried 3 or 4 times, it extinguishes the lamp and shuts down.

Secondly, I just acquired another emu. It's the cleanest i've ever seen. Looks bran new inside. not a speck of dust on the fan or pcbs. I'm starting to think maybe it never was used, since when you power it up, after homing the wheels and scanners, it just sits there. it doesn't attempt to strike the bulb at all. Again, I've tried multiple lamps, that work perfectly in other fixtures (plus, even if it was a bad lamp, it would TRY to strike the lamp, this one doesn't even try). It behaves the same whether its in setup, self-test, or normal operating mode. This one has the newer board in it, so I can't swap the board out without modifying the wiring, since the connectors are different, so I haven't tried another logic board in it, but I did try different eproms.

Any idea what might be wrong with these two birds?
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    It is the power supply board. I own 16 of these units and have had the same problem. Where are you located? I can repair it for you.
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    I'm in Seattle.

    What was the problem with the power supply board? I'm usually pretty good at diagnosing and repairing electronics, but for some reason these power supply boards confuse me.
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    The power supply boards are very confusing. There are a bunch of resisters on the lamp side of the board that tend to fail. It's hard to diagnose without seeing the board and having the ability to test it in one of my fixtures.
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    Look at pin 4 of the multicolored harness, and see if it goes to near 5 volts when the fixture tries to fire the lamp (yellow LED on). If not, the problem is the harness or logic. If you have that, then all the control of strike, main lamp power, etc. starts at IC4, an LM339 voltage comparator. (I just had one that would not lamp off - that was the culprit). Check the red/black to the lamp and see if DC is coming on when attempting to strike, as well as the red/black to the off board filter cap for the lamp power, and verify lamp power there as well. Oh, and the ignitor is controlled by triac TR1, so if it fails, you won't even see an attempt to strike. Also, the signal on pin 4 is interrupted by the thermal sensor, so if it or it's wiring has failed, the unit will never attempt to do anything with it's lamp - much like your second unit is behaving.

    Frankly, the easiest "shotgun" attempt would be to replace all 4 ICs - 1 through 4. Two are LM339, which I just got for $.49 each, and the other two are LM324, which should be a similar cost. They form the strike/interlock/power control logic in the Emu, and are all socketed, so are easy to change.

    As far as the supply is concerned, the schematic can make your head hurt, but once you figure it out, it isn't that bad. TR1 fires the igniter, controlled by opto IC5. SC1 and SC2 control lamp on off, and high/low, controlled via IC6. R23 gives power to the opto, and if the command to douse comes in, is pulled to ground via T4, based on the control voltage coming in to the card via the ribbon cable pin 4, as compared to a reference voltage determined by R34, R35, and R36, by IC4. (Other sections of these resistors and IC4 control the igniter as well . . . ).

    The other half of opto IC6 is driven by IC3, and that section of the circuit would appear to be a basic phase control circuit, much like a dimmer, that regulates lamp voltage, as well as providing the ability to switch power levels. That would parts of IC1 and transistors T1, T2, and T3.

    Once out of IC4, the ignitor signal passes through part of IC3 and IC2 where it is compared to a signal coming back from the igniter, which would appear to cut off the igniter once the lamp fires, with the current detector at the top of the schematic, with a section of IC2.

    While this won't cover all functionality of the power card, it should give you a start. Since the comparators (LM339) control damn near everything, as I said above, a real easy place to start would be to pop the $2 and change all four chips . . . unless a power component is out, that is what controls these cards . . .

    Hopefully this helps . . .

    - Tim
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    Thanks tim... I clearly need to check this board more often, as I just noticed your description. That helps alot. Think I'll have a look this weekend, and maybe I can get my last 2 remaining emus back in working condition.

    Thanks,

    Jeff
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    No problem, and good luck! Let me know if I can be of any additional help.

    - Tim
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