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Once	again need help fixing Orion HCCA 225 Digital Reference
Once	again need help fixing Orion HCCA 225 Digital Reference
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Old 21st February 2019, 03:19 AM   #151
Chopperbuilder is offline Chopperbuilder  United States
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Join Date: May 2018
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Amp powers up for a couple of minutes when it is cold then shuts down. When it is powered up I do have voltage at the MPSA06 drivers.



When it shuts down there is no voltage on pins 9 and 10 of the 494.
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Old 21st February 2019, 04:58 AM   #152
Perry Babin is offline Perry Babin  United States
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Pin 4 going high will stop the IC from producing pulses on 9 and 10.

Previously, you were having a problem of having drive pulses on one set of drivers but not the other. That has nothing to do with the output of the IC. There has to be another reason for it.
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Old 23rd February 2019, 02:34 AM   #153
Chopperbuilder is offline Chopperbuilder  United States
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I'm at a complete loss as to what could be driving the voltage up on pin 4.

Best I can tell, pin 14 drives pin 4 (attached a photo of the trace). The only things in that circuit are one electrolytic cap and one tantalum cap(see second photo). Those have both been replaced. Do you think it is possible one of those is causing it?
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Old 23rd February 2019, 06:08 AM   #154
Perry Babin is offline Perry Babin  United States
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Wasn't heating certain areas causing the problem to be worse?
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Old 23rd February 2019, 09:27 AM   #155
Chopperbuilder is offline Chopperbuilder  United States
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Yes it did. The heat gun is what put the amp in the state it is in now. Which is having to power it using the resistor you suggested to limit the current to keep the PS FETs from blowing. Also having no voltage on legs 1 and 2 of the MPSA06's, no voltage on pins 9 and 10 of the 494 and the on pin 4 of the 494 being too high.

I'm not a 100% certain which area was effected by the heat gun. The area that seem to be most effected, that I circled in yellow in post #142, I can find nothing reading out of specs.

Last edited by Chopperbuilder; 23rd February 2019 at 09:30 AM.
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Old 23rd February 2019, 12:58 PM   #156
Perry Babin is offline Perry Babin  United States
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If pin 4 is too high, connect it to pin 7 again and get it back to where it was.

Heat shouldn't cause the amp to malfunction. Even if that's not the only problem, it's something that needs troubleshooting. You may have to use something like a piece of cardboard to block the heat from heating everything in the area to narrow down what's so sensitive.
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Old 23rd February 2019, 04:36 PM   #157
Chopperbuilder is offline Chopperbuilder  United States
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The 10k resistor is still on pins 4 and 7. Should I remove it and put a jumper wire on it or try going to a lower ohm resistor?
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Old 23rd February 2019, 06:41 PM   #158
Perry Babin is offline Perry Babin  United States
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Go back to the jumper until you get the drive circuit repaired. Then back to the resistor.
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Old 23rd February 2019, 07:00 PM   #159
jkrokenberger is offline jkrokenberger  United States
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Oops

Last edited by jkrokenberger; 23rd February 2019 at 07:03 PM. Reason: Not pertinent information.
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Old 25th February 2019, 09:24 PM   #160
Chopperbuilder is offline Chopperbuilder  United States
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I solved the power imbalance that was going on which was causing the PS FETs to overheat. I had pulled the MSPA06's and the MSPA56's to test them. They tested good so I tested the pads for voltage, while I had them out of circuit. Found voltage on pad 2 of the left MSPA06 driver. Something conductive was on the board in that area. Not sure was it was as it wasn't visible. Cleaning the area removed it.



I also pulled the 494 cleaned that area of the board and replaced it with a new one. Pin 4 voltage is still high. I have installed the jumper back on it. I'm still at a complete loss as to what could possibly be causing it. Do you have any suggestions on what I should check or do next?
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