| Electronics > Repair |
| Power supply board damage - reversed polarity on two CONs |
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| vladc77:
Hello everyone, I accidentally incorrectly connected two connectors from the power supply board to the logic board of the Nakamichi CR-7A vintage deck. They both look the same. These are the CN4 to the CN5 cable connectors on schema. It resulted in some damage to the power supply board that I cannot identify. After connecting them properly, the deck stopped playing, rewind, or fast forward. I found out that may be reverse polarity is happening on the two connectors on the power supply board. These are CN40 and CN5. I need help to identify the reason for the voltage swap from +12V to -12V on pins 1 and 2 of the CN40 power supply board connector and the opposite on Pins 5 and 6 from -12V to +12V. In addition, the same voltage values are in the CN5 power supply board while they supposed to be different. It may be that the same failure affects both. I marked these connectors in red on the schema. I checked the capacitors and most resistors on the circuit board. they all seem to be OK. All fuses are good. I hope anyone more experienced can help to suggest what can cause this reverse polarity. Thank you in advance! Below are CN40 and CN5 voltage measurements on the power supply board. ------------------------------------------- CN40 ------------------------------------------- Pin 1: -12.2v (should be +12v) Pin 2: -12.2v (should be +12v) Pin 3: 0v (should be GND) Pin 4: 0v (should be GND) Pin 5: +12.3v (should be -12v) Pin 6: +12.3v (should be -12v) ------------------------------------------- ------------------------------------------- CN5 ------------------------------------------- Pin 1: -12.2v (should be +12v) Pin 2: -12.2v (should be +5.6v) Pin 3: 0v (should be -12v) Pin 4: 0v (should be GND) Pin 5: +12.3v (should be +15v) Pin 6: +12.3v (should be AC) ------------------------------------------- |
| MathWizard:
What voltages to you get after the 3 rectifiers, D401, 404, 407 ? So that would be from GND to the top of the caps C401, 410, 413. |
| vladc77:
Thanks MathWizard! Here are my voltage testing results. I also tested the voltage on rectifiers and IC401 since it is related to CN5. IC401 voltage is correct for all pins. ------------------------------------------- + sign is for positive pins and - for negative. ------------------------------------------- Capacitors ------------------------------------------- C401: + (+20.5V) | - (0V) C402: + (+20.5V) | - (0V) C406: + (0V) | - (-21V) --- C410: + (+9.3V) | - (0V) C413: + (+25.4V) | - (0V) C414: + (0V) | - (-24.5V) --- ------------------------------------------- Rectifiers voltage ------------------------------------------- D401: + (+20.5V) | - (-21V) | voltage with leads connected to + and - = +41.5v --- D404: + (+9.4V) | - (0) | voltage with leads connected to + and - = +9.4v --- D407: + (+25.4V) | - (-25.5V) | voltage with leads connected to + and - = +50.4v ------------------------------------------- ------------------------------------------- IC 401 ------------------------------------------- Pin 1 has to be -2v I have -2.1v Pin 2 has to be 0v I have 0v Pin 3 has to be 0v I have 0v Pin 4 has to be -12v I have -12v Pin 5 has to be +5v I have +5v Pin 6 has to be +5v I have +5v Pin 7 has to be +2 I have +2v Pin 8 has to be +12v I have +12v ------------------------------------------- |
| MathWizard:
Those sound ok, the op-amp IC401 has it's Vcc =+12V on p8 and should be directly connected to CN40-p1,2 and CN5-p1. IC401's Vee=-12V is p4, and that should go right to CN4-p5,6 and CN5-p3 |
| vladc77:
Do all voltage values sound ok, including caps and rectifiers? Please clarify. What then can cause getting incorrect voltage values for CN40 and CN5? Those are not correct for all pins. Thanks. |
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