nodols
Junior Member
Posts: 75
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Post by nodols on Jun 18, 2022 20:45:09 GMT -5
In the mini transformer, wires from the mains are directly connected to the minitransformer, an ohms test on the terminals will give about 90 ~ 100ohms reading. An ohms test on the - Amp Transformer gives close to 0 ohms - I have them disconnected, also according to the schematic those wires are directly going to the mains of the amp transformer. I'm just wondering why you think amp transformer is good? The short answer is: not all transformers have the same resistance. The resistance is based on the number of turns and the gauge of wire. Testing resistance on a transformer will not determine if it is bad or not unless the reading is open. A shorted transformer must be tested differently and I do not believe we are there yet. Other problems must be determined first which is what we are trying to do. Well this is a relief. I tried looking over at youtube, some toroidal transformers had about 4 ohms on the primary and the guy said it was shorted, and the other one which was not shorted had 8 ohms. I guess toroidal has lesser ohm reading than EI transformers. |
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Post by mastertech on Jun 18, 2022 20:53:24 GMT -5
Ok, so, this does not make any sense. With the harness connected at both ends and S801 switch on, (please leave this switch on for testing and do not turn it off unless I tell you to) you only have a milivolt reading on pin 1 of CY073. When you disconnect the harness at CY073 your voltage goes up to +3.8v at pin 1 of CY073. This change in voltage indicates there is a short on the Primary Unit board. So when you test the resistance across pins 1 and 3 of CX073 it should show a low resistance to indicate a short of pin 1 to ground. But your readings do not indicate this. This makes no sense.
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nodols
Junior Member
Posts: 75
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Post by nodols on Jun 18, 2022 21:10:35 GMT -5
Ok, so, this does not make any sense. With the harness connected at both ends and S801 switch on, (please leave this switch on for testing and do not turn it off unless I tell you to) you only have a milivolt reading on pin 1 of CY073. When you disconnect the harness at CY073 your voltage goes up to +3.8v at pin 1 of CY073. This change in voltage indicates there is a short on the Primary Unit board. So when you test the resistance across pins 1 and 3 of CX073 it should show a low resistance to indicate a short of pin 1 to ground. But your readings do not indicate this. This makes no sense. ok, it is 4.35kohms on pins 1 and 3 of CX073. This is with harness connected on both ends, and S801 in the ON position. |
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Post by mastertech on Jun 18, 2022 21:13:29 GMT -5
Ok, can you reverify the voltage on pin 1 of CY073 with the harness connected and then harness disconnected.
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nodols
Junior Member
Posts: 75
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Post by nodols on Jun 18, 2022 21:37:21 GMT -5
Ok, can you reverify the voltage on pin 1 of CY073 with the harness connected and then harness disconnected. I too am confused, but I found out after several tries and even took a video of it. When everything was connected, in the first 4 to 5 seconds the voltage at pin 1 of CX073 will be at 1.5V, after about 5 seconds it will drop to 800mV. When I disconnected one side, it stays the same at mV no changes after several seconds of waiting. |
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Post by mastertech on Jun 18, 2022 21:46:43 GMT -5
What is it if you test at CY073 instead? Like you did the first time. But disconnect at CX073 instead of CY073 while testing on CY073.
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nodols
Junior Member
Posts: 75
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Post by nodols on Jun 18, 2022 21:49:41 GMT -5
What is it if you test at CY073 instead? Like you did the first time. But disconnect at CX073 instead of CY073 while testing on CY073. I got a pretty stable 3.89V at pin 1 of CY073, and disconnected at CX073. Regardless of how many tries, no change even after how many seconds of measuring from the same pin 1 of CY073. |
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Post by mastertech on Jun 18, 2022 21:57:01 GMT -5
Ok, and I am guessing it then drops to a milivolt reading if you connect CX073 while monitoring voltage. And then comes back up to 3.89v if then CX073 disconnected?
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nodols
Junior Member
Posts: 75
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Post by nodols on Jun 18, 2022 22:02:55 GMT -5
Ok, and I am guessing it then drops to a milivolt reading if you connect CX073 while monitoring voltage. And then comes back up to 3.89v if then CX073 disconnected? Yes, with both ends connected CX to CY it will drop to the 800mV range, sometimes if it feels crazy it will reach the 1.1V range, but rarely and stays there. When I turn if off and on again it will go back to the 800mV range. And yes, when I disconnect any end of the harness, then I measure from pin 1 of CY073, it is a stable 3.89V, no changes whatsoever even after several seconds of waiting. Which would make me think it is the minipower supply that keeps the voltage at pin 1 dropping to the low 800mV. |
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nodols
Junior Member
Posts: 75
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Post by nodols on Jun 18, 2022 22:16:28 GMT -5
Ok, and I am guessing it then drops to a milivolt reading if you connect CX073 while monitoring voltage. And then comes back up to 3.89v if then CX073 disconnected? This is exactly true. I tried not the unit off when connecting and disconnecting CY073. When connected it is 800mV, then I disconnected voltage went to 3.89 to 4V, connected it again drops starts at 1.5volts then drops to 800mV, disconnected again goes back to 4 volts, connected again drops to 800mV. Could the minipower supply be the problem? |
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Post by mastertech on Jun 18, 2022 22:17:27 GMT -5
Right. So on the mini power supply there are a few things connected to that line. You can first try testing all the transistors on that line for close to short reading.
Unit unplugged and meter on diode test, check: TR704, TR705, TR707, TR708, TR709, TR710, TR711
If any test bad remove them and then retest voltage at pin 1 with harness connected at both ends. If none test bad remove R710 and then test voltage at pin 1 with harness connected.
I will check back tomorrow and see how you made out.
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nodols
Junior Member
Posts: 75
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Post by nodols on Jun 18, 2022 22:27:51 GMT -5
Right. So on the mini power supply there are a few things connected to that line. You can first try testing all the transistors on that line for close to short reading. Unit unplugged and meter on diode test, check: TR704, TR705, TR707, TR708, TR709, TR710, TR711 If any test bad remove them and then retest voltage at pin 1 with harness connected at both ends. If none test bad remove R710 and then test voltage at pin 1 with harness connected. I will check back tomorrow and see how you made out. That's the thing, there are some of those transistors that are bias resistor built-in transistor (BRT) which I don't actually know how to test. lol |
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Post by mastertech on Jun 18, 2022 22:42:55 GMT -5
That is why I said close to short. If a reading is not close to short then it may be ok. Which is then why I said to remove the resistor. That will eliminate all but 2 of those transistors.
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nodols
Junior Member
Posts: 75
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Post by nodols on Jun 19, 2022 22:53:41 GMT -5
That is why I said close to short. If a reading is not close to short then it may be ok. Which is then why I said to remove the resistor. That will eliminate all but 2 of those transistors. All transistors seem to be good, most of them are on the back side, all of them have junction voltage and no shorted ones and junction voltages doesn't drop lower than 0.45V most are in the .55 to .6xxV. I haven't removed the resistor yet and haven't had the chance to do a voltage test yet. I have it disassembled for now, kind of tedious to assemble again there are 2 boards stack top of each other and a lot of harnesses and screws. Will do the resistor testing and removal last before I put back everything. |
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nodols
Junior Member
Posts: 75
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Post by nodols on Jun 21, 2022 10:42:39 GMT -5
That is why I said close to short. If a reading is not close to short then it may be ok. Which is then why I said to remove the resistor. That will eliminate all but 2 of those transistors. All transistors seem to be good, most of them are on the back side, all of them have junction voltage and no shorted ones and junction voltages doesn't drop lower than 0.45V most are in the .55 to .6xxV. I haven't removed the resistor yet and haven't had the chance to do a voltage test yet. I have it disassembled for now, kind of tedious to assemble again there are 2 boards stack top of each other and a lot of harnesses and screws. Will do the resistor testing and removal last before I put back everything. I got a defective reading here. IC701, it is a regulator that is supposed to out a 5 volts, but only gives out 1V. I removed it and supplied 12V on the IN and measured the OUT side. Only gives out 1V. I believe I found out the culprit.  Thank you MT. I will still need to test this toroidal transformer if this really is working, and not the one that's causing the foul smell. Also need to recheck the front panel for other solder joints, as I found some on it before. Will probably need another thorough check. Do you think that foul smell would account for another fault on the system? |
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