Trying to fix a JVC HM-DH30000U VCR (NTSC/US) with a bad power supply and I need some advice. This seems like something that should be simple, or at least a great learning opportunity. I'm not an expert so any level of advice is welcome, and I invite you to assume I know nothing.
From what little I know of power supply design, this one was poorly designed in that it stays hot whenever the unit is plugged in. I expect that constant heat has a tendency to cause breakdowns. There are no obvious signs of short or overheating. (I.e. no discolorations on the board or black marks, no discolored resistors etc...)
I have two of these units, one is fully working and this one will not power on. When first plugged in, the fan will sometimes spin for a second or less as though it's trying to start but gives up. I believe that the problem is isolated to the power supply because if I swap the power supply from the working VCR to this unit, this unit works normally.
The service manual can be found here: <snip>
The power supply schematic is on page 76 of that PDF.
Just probing around the power supply board one obvious problem I've found is that pins 1, 2, 3, 4, 11, and 12 on CN5302 (which goes to the digital video interface) are not showing the expected voltages. Instead 3.3v, 2.2v, and 2.5v respectively they're both showing just a few mV.
I've concentrated my troubleshooting in the area of the four voltage regulator ICs that supply power to those pins. All four of these ICs are PSQEV3's (datasheet).
Pins CN5302[1] and [2] are driven by the output of IC5302, Pins CN5302[3] and CN5302[4] are driven by the output of IC5303, and pins CN5302[11] and CN5302[12] are driven by IC5305. So one of the symptoms of the problem is that IC5302, IC5303, IC5305 are not outputting voltage.
The input voltages to those ICs look fine. IC5302 and IC5304 share an input rail and both read about 6.7v. IC5304 is outputting the expected voltage so I expect that's correct. Likewise IC5303 shares an input rail with IC5305, and they're showing about 4.9v (which makes sense considering they're supposed to have lower output than the other two).
The problem, I think, is that the "On/Off" pins for IC5302, IC5303 and IC5305 are all staying low so the regulators aren't being activated. Those three are all connected to the same signal path. IC5304 (which is working) has a different signal path for On/Off and it is working correctly. The voltage on it's ON/OFF pin is 2.4v. Since the others are the exact same chip as IC5304 (which is working normally), I temporarily bridged the ON/OFF pin from IC5304 to the ON/OFF pin on the other three to see if that would activate the other regulators, but instead it pulled IC5304's ON/OFF pin low too. Resistance between the common ON/OFF line shared by IC5302, IC5303, and IC5305 and ground is about 6.8k Ohms, so I don't *think* I have a short.
FWIW, I've tested this both with the power supply connected to the unit, and with the power supply disconnected.
Here are the steps I've taken so far:
- Checked for shorts to ground at the connectors, at Q5302, Q5303, IC5305, IC5303, IC5302, D5315, D5312
- Checked all of the electrolytic caps and replaced any that were out of spec (ESR or capacitance)
- Replaced all remaining electrolytic caps
- Replaced the power supply fuse (the old one checks out fine)
- Checked diode D5312 - checked fine with DMM
- Swapped diode D5312 and D5315 to see if the problem followed the diode (if it did, I expected to see CN5302[5] output the wrong voltage, but its output was the expected 3.3v even with the other diode in the path).
- Replaced IC5302 and IC5303
I should add that I'm not sure the problem has anything to do with those regulators.
Moderator edit: Link to service manual deleted, suspicious site, malware detected.
From what little I know of power supply design, this one was poorly designed in that it stays hot whenever the unit is plugged in. I expect that constant heat has a tendency to cause breakdowns. There are no obvious signs of short or overheating. (I.e. no discolorations on the board or black marks, no discolored resistors etc...)
I have two of these units, one is fully working and this one will not power on. When first plugged in, the fan will sometimes spin for a second or less as though it's trying to start but gives up. I believe that the problem is isolated to the power supply because if I swap the power supply from the working VCR to this unit, this unit works normally.
The service manual can be found here: <snip>
The power supply schematic is on page 76 of that PDF.
Just probing around the power supply board one obvious problem I've found is that pins 1, 2, 3, 4, 11, and 12 on CN5302 (which goes to the digital video interface) are not showing the expected voltages. Instead 3.3v, 2.2v, and 2.5v respectively they're both showing just a few mV.
I've concentrated my troubleshooting in the area of the four voltage regulator ICs that supply power to those pins. All four of these ICs are PSQEV3's (datasheet).
Pins CN5302[1] and [2] are driven by the output of IC5302, Pins CN5302[3] and CN5302[4] are driven by the output of IC5303, and pins CN5302[11] and CN5302[12] are driven by IC5305. So one of the symptoms of the problem is that IC5302, IC5303, IC5305 are not outputting voltage.
The input voltages to those ICs look fine. IC5302 and IC5304 share an input rail and both read about 6.7v. IC5304 is outputting the expected voltage so I expect that's correct. Likewise IC5303 shares an input rail with IC5305, and they're showing about 4.9v (which makes sense considering they're supposed to have lower output than the other two).
The problem, I think, is that the "On/Off" pins for IC5302, IC5303 and IC5305 are all staying low so the regulators aren't being activated. Those three are all connected to the same signal path. IC5304 (which is working) has a different signal path for On/Off and it is working correctly. The voltage on it's ON/OFF pin is 2.4v. Since the others are the exact same chip as IC5304 (which is working normally), I temporarily bridged the ON/OFF pin from IC5304 to the ON/OFF pin on the other three to see if that would activate the other regulators, but instead it pulled IC5304's ON/OFF pin low too. Resistance between the common ON/OFF line shared by IC5302, IC5303, and IC5305 and ground is about 6.8k Ohms, so I don't *think* I have a short.
FWIW, I've tested this both with the power supply connected to the unit, and with the power supply disconnected.
Here are the steps I've taken so far:
- Checked for shorts to ground at the connectors, at Q5302, Q5303, IC5305, IC5303, IC5302, D5315, D5312
- Checked all of the electrolytic caps and replaced any that were out of spec (ESR or capacitance)
- Replaced all remaining electrolytic caps
- Replaced the power supply fuse (the old one checks out fine)
- Checked diode D5312 - checked fine with DMM
- Swapped diode D5312 and D5315 to see if the problem followed the diode (if it did, I expected to see CN5302[5] output the wrong voltage, but its output was the expected 3.3v even with the other diode in the path).
- Replaced IC5302 and IC5303
I should add that I'm not sure the problem has anything to do with those regulators.
Moderator edit: Link to service manual deleted, suspicious site, malware detected.