Help fixing 2 PVM-14M2U

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soviet9922
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Help fixing 2 PVM-14M2U

Post by soviet9922 »

A few days ago got lucky but not so lucky and was able to acquire two PVM-14M2U.
Externally and internally they look great clean and in excellent condition but they are faulty.

Have experience fixing monitors and tv's have all the necessary tools but never seen issues like this maybe someone can point me
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Monitor number 1 turns on fine they are several problems:
The screen is full of retrace lines.
On the sides of the screen you can see the screen is bending like this -> )( and there's some ghosting in the image also they are a couple of like big dark smushes in the picture.
But there's no OSD and the brightness and contrast controls don't seem to do anything.
What works is:
All the buttons work, pressing the wide screen will flatten the image the input, etc will get the correct thing to happen, the inputs work because you can hear the audio input from them and the small led inside the buttons work.
The "blue only key" will make the screen red and flickering the PSU will make clicking noises during this until the button is pressed again and "blue only" is disabled.
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Monitor number 2 turns one you can hear the high voltage kick in and there's some little glow from the screen but none of the buttons work, the small LEDs in them don't light there's no audio and inputs don't switch contrast and brightness do nothing. There's no OSD or anything else.

So disassembled them and tested the basics, the PSUs are on a separate module from the boards so was easy to check the voltages and they seem to be OK in both units.
Tried swapping the PSUs between the monitor but there are no effect same issues in both.

On unit number 2 thought may the main IC NECD78014 could be bad if socketed so swapped it between units but this don't change anything both sets continue showing the same issues.
Also, check for the presence of VDD 5v on the CPU and is present.

Any ideas where to check first?
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This is from set 1:
Image

Set number 2 there's not much to show.

here is the service manual:
https://mega.nz/file/Exl3ARhI#1XjYEdYo3 ... onfosvqgmY
Last edited by soviet9922 on Sat Mar 25, 2023 11:42 pm, edited 3 times in total.
MKL
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Re: Help fixing 2 PVM-14M2U

Post by MKL »

Do you have 180V at C713 on the neckboard?
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soviet9922
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Re: Help fixing 2 PVM-14M2U

Post by soviet9922 »

MKL wrote:Do you have 180V at C713 on the neckboard?
monitor n1 has 186v on it.
monitor n2 has 113v on it.
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Re: Help fixing 2 PVM-14M2U

Post by MKL »

113v i.e. roughly the same as the +B (115v) means the flyback transformer (T501) is not working and there could be a number of reasons for that. Check for 13v on pin 11 of IC507.
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soviet9922
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Re: Help fixing 2 PVM-14M2U

Post by soviet9922 »

MKL wrote:113v i.e. roughly the same as the +B (115v) means the flyback transformer (T501) is not working and there could be a number of reasons for that. Check for 13v on pin 11 of IC507.

Have 5.6v in pin 11 of IC507
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Re: Help fixing 2 PVM-14M2U

Post by MKL »

Making sure you're measuring correctly. Yellow arrow = pin 11, red arrow = ground (heat sink).

https://i.imgur.com/ouDRyvD.jpg

If you are indeed measuring 5.6V there, check voltage on either side of R556 (one side is the same as pin 11, other side is +B/115V).
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soviet9922
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Re: Help fixing 2 PVM-14M2U

Post by soviet9922 »

MKL wrote:Making sure you're measuring correctly. Yellow arrow = pin 11, red arrow = ground (heat sink).

https://i.imgur.com/ouDRyvD.jpg

If you are indeed measuring 5.6V there, check voltage on either side of R556 (one side is the same as pin 11, other side is +B/115V).
Yes checked using the same pin and ground as in the picture.

Image
free url host

Checked resistor 556 and is 5.6v in one side and 114v in the other.
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Re: Help fixing 2 PVM-14M2U

Post by MKL »

That's the problem, 5.6v is not enough to run the horizontal oscillator (normally 13V, min. 12V) so there's no horizontal drive pulse from pin 10 and without that the flyback doesn't turn on. 13V is obtained from the 115V through a shunt regulator circuit consisting of R556, C552 and a 13V zener diode which is built in IC507 (cathode = pin 12, anode = ground). You can check or replace these parts except for the zener for which you would need to replace the whole IC.
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soviet9922
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Re: Help fixing 2 PVM-14M2U

Post by soviet9922 »

MKL wrote:That's the problem, 5.6v is not enough to run the horizontal oscillator (normally 13V, min. 12V) so there's no horizontal drive pulse from pin 10 and without that the flyback doesn't turn on. 13V is obtained from the 115V through a shunt regulator circuit consisting of R556, C552 and a 13V zener diode which is built in IC507 (cathode = pin 12, anode = ground). You can check or replace these parts except for the zener for which you would need to replace the whole IC.

Tested the resistor 556 and is 12k like it should, the cap C552 was a little low read 200 uF and is marked as 220 replaced the part anyway and the voltage continue the same.

So ordered a new IC to replace the one there and test, will update later when i get it.

Maybe you also know what could be the issue to the other set "Numer 1" in the thread description maybe ?.

Thank you very much for the help.
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Re: Help fixing 2 PVM-14M2U

Post by MKL »

12V present on the neckboard? Replace the neckboard with that of the other unit.

Description for monitor no. 2 says "you can hear high voltage kick in and there's some little glow from the screen". This is not possible if the flyback doesn't work (for the above reason). Is this only for a few seconds? Check the G2 voltage (400VDC+) on the neckboard (DMM probes need to be already attached when you turn the monitor on so you can see if the DMM display shows any voltage even if just for a couple of seconds. G2 doesn't come from the flyback but from the H drive pulse from the HOT (Q501) so presence of G2 implies presence of H drive from IC507.
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soviet9922
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Re: Help fixing 2 PVM-14M2U

Post by soviet9922 »

MKL wrote:12V present on the neckboard? Replace the neckboard with that of the other unit.

Description for monitor no. 2 says "you can hear high voltage kick in and there's some little glow from the screen". This is not possible if the flyback doesn't work (for the above reason). Is this only for a few seconds? Check the G2 voltage (400VDC+) on the neckboard (DMM probes need to be already attached when you turn the monitor on so you can see if the DMM display shows any voltage even if just for a couple of seconds. G2 doesn't come from the flyback but from the H drive pulse from the HOT (Q501) so presence of G2 implies presence of H drive from IC507.

On monitor no. 1 G2 is 749v 12v present at the neckboard 180v at c713.

On monitor no. 2 Is exactly like you say G2 will start at 400v when power is applied and quickly drop to 103v in a few seconds, also 12v is present on the neck board.

Tried swapping the neckboards between the monitors but no voltage changes and all symptoms are like in the beginning.
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Re: Help fixing 2 PVM-14M2U

Post by MKL »

I'd wait before replacing IC507. Measure the voltage at R556/IC507 (11) with probes already attached at power on and see if in the first few seconds it is 13V and then drops. Also measure the voltage at the cathodes of D510 and D514 where 15V and 24V are expected respectively.
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soviet9922
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Re: Help fixing 2 PVM-14M2U

Post by soviet9922 »

MKL wrote:I'd wait before replacing IC507. Measure the voltage at R556/IC507 (11) with probes already attached at power on and see if in the first few seconds it is 13V and then drops. Also measure the voltage at the cathodes of D510 and D514 where 15V and 24V are expected respectively.

Pin 11 on IC507 will start at 12v and quickly drop to 5.6v.

D510 cathode will start at 12v and quickly fall to 1.6v also.

D514 cathode will start at 20v and quickly fall to 1.6v, that was the first few times that I tested.
But later re-tested several times and don't get anything at the cathode side at power on 0.20v, the anode will have 17+ volts and quickly drop to 1.6v.
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Re: Help fixing 2 PVM-14M2U

Post by MKL »

From the flyback trasformer up to the anode it is a peak-to-peak voltage so you can't have DC there because it's the diode the rectifies it to DC. Check again after making sure D514 is good. The 24V is used among other things as a supply for the horizontal section of the deflection IC (IC507). The startup voltage comes from the +B line as stated in the above posts. Then the 24V is superimposed to it through D517 and R558.

Another voltage to check is the one used for the x-ray protection. This comes from pin 7 of the flyback and is rectified by D533 and sent to pin 11 of IC500. The IC then sends out a voltage from pin 8 to pin 6 of IC507 which turns off the oscillator if this voltage is too high. So check the voltage at the cathode of D533 (or TP503) at power on as well as the voltage on pin 6 of IC507 which shouldn't be (much) higher than the 0.2V shown in the schematics.
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soviet9922
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Re: Help fixing 2 PVM-14M2U

Post by soviet9922 »

MKL wrote:From the flyback trasformer up to the anode it is a peak-to-peak voltage so you can't have DC there because it's the diode the rectifies it to DC. Check again after making sure D514 is good. The 24V is used among other things as a supply for the horizontal section of the deflection IC (IC507). The startup voltage comes from the +B line as stated in the above posts. Then the 24V is superimposed to it through D517 and R558.

Another voltage to check is the one used for the x-ray protection. This comes from pin 7 of the flyback and is rectified by D533 and sent to pin 11 of IC500. The IC then sends out a voltage from pin 8 to pin 6 of IC507 which turns off the oscillator if this voltage is too high. So check the voltage at the cathode of D533 (or TP503) at power on as well as the voltage on pin 6 of IC507 which shouldn't be (much) higher than the 0.2V shown in the schematics.
Thanks, took me a wile to check and re-check all of this.

Diode 514, removed it and check it on my small component tester, and shows up as a diode check on the multimeter the current will pass in one direction and not in the other so seems ok.
But when turning on the set can only get very little voltage there and will quickly drop to 0.

Monitor 2
IC507-PIN6=5.5v
IC500-PIN11=0.2v
D533=0.2v(starts at 120v and drops fast)

So to check against monitor 1 that at least turns on
D533=125v
IC500-PIN11=125v
IC507-PIN6=0v
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Re: Help fixing 2 PVM-14M2U

Post by MKL »

Suck solder off IC507 (6) or break the line some other way and see if the monitor turns on and stays on in which case don't leave it on for long just enough to see it doesn't turn off as quickly as before. It would help to measure the anode voltage and check the HOT collector waveform at that point as that would tell if some of the components tied to that line are responsible for an excessive anode voltage and consequent HV hold down. If all that is regular you should start checking the parts marked with a half-black half-white square.
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