Bringing back a PVM-14M4U back to life using a hairdryer

[tongshadow]

I recently acquired an PVM-14M4U that had, well, still has technically, the red/orange tally of death. It seems to be a known problem on these models which can be caused by different reasons.
In my case however all it took to make it work perfectly again was to blow hot air on the main circuit board. Now, I've ruled out the power supply and the other boards, so there is some issue on the main board.

So I ask this question... what could a relatively short stream of hot air affect on the board to bring it back to life? Could it be a cold solder joint? Or perhaps the infamous capacitors? Has anyone here heard of something like this or had a similar experience in electronics in general? Im looking for a more permanent fix.

[NJRoadfan]

Was it a permanent fix, or did the board exhibit failure again after it cooled off? If it continues to work, it might have been a cracked solder joint that re-flowed, but that is going to need quite a bit of heat focused on parts of the board.

I have an audio receiver here that won't turn on unless its above a certain room temperature. I suspect its bad caps in the standby power supply, but haven't gotten around to replacing them yet. The rest of the circuit is fairly straight forward (bridge rectifier, some zener diodes, resistors, and a transistor) There is a noticeable buzz in the audio output when the unit is cold, so likely needs a re-cap all around.

[tongshadow]

Was it a permanent fix, or did the board exhibit failure again after it cooled off? If it continues to work, it might have been a cracked solder joint that re-flowed, but that is going to need quite a bit of heat focused on parts of the board.

When it fully turns on theres no need to apply the heat anymore, it works perfectly. It's cold starting that is the issue.
Now, I hope it's not a cold joint on an SMD component because it's going to be very hard to reflow every tiny joint.

[Dochartaigh]

Did you read or try the fix that has worked for quite a few people with this quasi-common tally light fault? Don't even know which board it is tbh, just know it's helped a few people. It's the first link when you google this (and I archived the document further down on that post after his link went down):

https://www.reddit.com/r/crtgaming/comm ... _response/

Could of course be something different on your monitor, but a good place to start if it happens to help.

[tongshadow]

Did you read or try the fix that has worked for quite a few people with this quasi-common tally light fault? Don't even know which board it is tbh, just know it's helped a few people. It's the first link when you google this (and I archived the document further down on that post after his link went down):

https://www.reddit.com/r/crtgaming/comm ... _response/

Could of course be something different on your monitor, but a good place to start if it happens to help.

Yes, it was one of the first things I read to attempt solving my issue but the PSU was good. The red light seems to be a general failure code, like the infamous 360's 3 red lights.
Going into more detail, what happens is that something on the A Board is causing the 15V line to drop to only 12V, and consequently the 12V line drops to 10V. I tried to isolate the issue by removing components down the line but then it became a nightmare when I noticed the 12V line is basically everywhere!

So far I have reflowed the pins of all through-hole ICs and of some components as well, but not them all. Im thinking about replacing the smaller capacitors but I always thought capacitors worked better when cold, so who knows...

[Dochartaigh]

I always thought capacitors worked better when cold, so who knows...

Not at all. One of the signs that a problem actually IS caps (I say that because people like to say to EVERY crt issue "replace the caps" when that's not it a lot of the time) is if the problem goes away AFTER the TV warms up, then it COULD be caps since caps work better when they're warmed up (vs. cold).

[tongshadow]

Now that I think about it, I had a samsung lcd that wouldnt turn on right away so you had to keep the power button pressed. There was also a distinct capacitor noise.

I know I should replace most caps as they're aged now, but there are 90+ caps on this boards so Im trying to narrow it down.

[NJRoadfan]

Tackle the power supply first. The +12v rail (and likely others) fluctuating is going to cause all sorts of problems around the set. Old dried out electrolytic caps will vary in capacitance/ESR depending on the temperature.

[tongshadow]

It's not the PSU, it generates every voltage perfecty when disconnected and isolated from the issue. The 12v rail on the M4U is derived from the 15v rail.

[Syntax]

Use a can of freeze spray while the units on to help find the faulty area.

[tongshadow]

Changed about 70% of the caps and yet the issue persists... I really hope it's NOT one of the minuscule SMD components.
What exactly could be the issue? I know for a fact a hairdryer isnt hot enough to melt solder, so maybe I should discard cold solder joints?
Again, the monitor works perfectly after turning on, but it wont startup again if it's cold.

[tongshadow]

Ok, after narrowing down the hot air to the area around the flyback and heatsinks, and noticing it was turning on faster than blowing air to the other side, I changed a couple of small capacitors and the big 220uf/160v one. And now it's turning on perfectly, even in this cold weather!

Some valuable lessons learned from this experience:
-If it works, but not quite right, it's likely caps
-If temperature is a factor in fixing the issue, it's probably caps
-Caps around heatsinks suffer a lot
-Unconventional methods can be more efficient than being technical
-PVMs and professional equipment are so robust and well engineered that eventual failures can be caused by the weakest link, electrolytic capacitors

So there you go, I'm glad to have brought some closure to this because, usually, it doesnt end well and the fix could've been just a part that costs a quarter.

[matt]

Can you share what capacitors you changed? I know somebody who has a PVM-20M2 with the same problem as yours - low 15v/12v with the red tally light. The power supply is fine and most of the usual "problem" capacitors had already been changed by the time I took a look at it, but it didn't help. I'd be curious if the ones you changed were missed and if it would make a difference.

[tongshadow]

Can you share what capacitors you changed? I know somebody who has a PVM-20M2 with the same problem as yours - low 15v/12v with the red tally light. The power supply is fine and most of the usual "problem" capacitors had already been changed by the time I took a look at it, but it didn't help. I'd be curious if the ones you changed were missed and if it would make a difference.

Sure:
C518 (big cap next to the FBT) - 220uf/160v
C529 (hugging the above cap) - 0.47uf/50v
C531 (next to the FBT) - 47uf/25v
C579 (I think, Im looking at the .pdf and it's pretty hard to read) - 100uf/50v
C588 (right next to the H-Center potentiometer, between 2 other caps ) - 10uf/50v
C1508 - 4.7uf/50v

https://i.imgur.com/XEaYSAY.jpeg
https://i.imgur.com/oXdaS2T.jpeg

Note: These are old pictures and when I got this monitor it had already been serviced by someone else. The caps sticking out have been changed or fixed.

[matt]

Thanks, that's very helpful. Hopefully it will work!

[tongshadow]

Post-mortem analysis now that I got a proper ESR/Capacitor tester, and here's what I got:

C518 - 220uf/160v - 191uf/19 ESR
C529 - 0.47uf/50v - 683pf/ no ESR reading
C1508 - 4.7uf/50v - 5.1uf/66 ESR

So plenty of bad caps with very high ESR readings, the 0.47uf one is so bad that tester cant even get a proper ESR reading. Capacitors C518 and C529 are part of the horizontal deflection circuit and are close to heat sources, so they were under very stressful conditions.

Im not expert when it comes to electronics, but C529 is in series with the transistor responsible for generating horizontal oscilation pulses into the horizontal deflection transformer, so it stands to reason that's a point of failure since no horizontal oscillation = no high voltage = no other flyback-derived voltages being generated. So this was probably THE culprit.

C518 seems to be a filter capacitor and is in parallel with many other circuits, including the flyback circuit and 180V line. And while I dont think it was the main culprit, the high ESR could've eventually led to other failures.

Like I said before, very robust and well-engineered circuit but capacitors are the weakest link. I dont recommend replacing them all because most capacitors outside the high heat/high frequency areas are perfectly fine and this monitor has more than 100 capacitors. I do recommend getting a tester/tool that can read ESR in circuit and inspect the capacitors close to heatsinks. While it's not possible to measure capacitance in-circuit, if the ESR is bad then that's enough reason to replace it.

[deezdrama]

Post-mortem analysis now that I got a proper ESR/Capacitor tester, and here's what I got:

C518 - 220uf/160v - 191uf/19 ESR
C529 - 0.47uf/50v - 683pf/ no ESR reading
C1508 - 4.7uf/50v - 5.1uf/66 ESR

So plenty of bad caps with very high ESR readings, the 0.47uf one is so bad that tester cant even get a proper ESR reading. Capacitors C518 and C529 are part of the horizontal deflection circuit and are close to heat sources, so they were under very stressful conditions.

Im not expert when it comes to electronics, but C529 is in series with the transistor responsible for generating horizontal oscilation pulses into the horizontal deflection transformer, so it stands to reason that's a point of failure since no horizontal oscillation = no high voltage = no other flyback-derived voltages being generated. So this was probably THE culprit.

C518 seems to be a filter capacitor and is in parallel with many other circuits, including the flyback circuit and 180V line. And while I dont think it was the main culprit, the high ESR could've eventually led to other failures.

Like I said before, very robust and well-engineered circuit but capacitors are the weakest link. I dont recommend replacing them all because most capacitors outside the high heat/high frequency areas are perfectly fine and this monitor has more than 100 capacitors. I do recommend getting a tester/tool that can read ESR in circuit and inspect the capacitors close to heatsinks. While it's not possible to measure capacitance in-circuit, if the ESR is bad then that's enough reason to replace it.

Good info here. I recently picked up a 20m2u with same exact issue. The power board is outputing all voltages but the 15v output is 12v when a board connector is plugged in.
I checked a few caps with my peak esr meter in circuit and esr is high on most of them. Ive fixed alot of funky issues with 40 series pvms replacing power and deflection circuit caps.
Looks like im going to have to order more caps to do full deflection and power circuit.
I had 5v regulators on hand because I read those are usually the issue for red tally light, its funny we always give crap to the guys who blame every issue on caps but alot of the time it is the capacitors and im going to make it common practice to replace deflection circuit caps at least when I have a crt open.... Its preventative maintenance at this point on components that will be going out sooner rather than later.

Good info.... Hopefully I find the same fix

[tongshadow]

Good info here. I recently picked up a 20m2u with same exact issue. The power board is outputing all voltages but the 15v output is 12v when a board connector is plugged in.

Mine did the same thing and I assumed it was a bad regulator. Seems like it could be caps too, hope it is.

[deezdrama]

Good info here. I recently picked up a 20m2u with same exact issue. The power board is outputing all voltages but the 15v output is 12v when a board connector is plugged in.

Mine did the same thing and I assumed it was a bad regulator. Seems like it could be caps too, hope it is.

I recapped the deflection circuit last weekend, was missing a couple cap values so made another mouser order and hopefully will get to finish this recap this weekend, ill post my results.

[deezdrama]

Good info here. I recently picked up a 20m2u with same exact issue. The power board is outputing all voltages but the 15v output is 12v when a board connector is plugged in.

Mine did the same thing and I assumed it was a bad regulator. Seems like it could be caps too, hope it is.

Got done recapping the deflection circuits. I replaced all 17 caps in savon pats kit and swapped the values he suggests with his kit (someone posted the cap info on reddit) and also swapped out that big 220uf 160v cap by the flyback and all the other caps directly near the flyback.

She fired up, i hear the HV whine,degaus, hear a loud pop everytime I fire it on which im not sure what it is, maybe ill clean under the anode cap again..... Anyway, I get a "no sync" message that fades away after a few seconds.... Tried to connect a snes through svideo but cant change inputs. Seems none of the front panel buttons work.
Ive read if the remote led indicator is on then it could be locked into a user preset which disables the front buttons but the remote indicator light is not lit, cant bring up the menu, change source or anything.
Any ideas?

https://ibb.co/j4WMGyH

[tongshadow]

Good info here. I recently picked up a 20m2u with same exact issue. The power board is outputing all voltages but the 15v output is 12v when a board connector is plugged in.

Mine did the same thing and I assumed it was a bad regulator. Seems like it could be caps too, hope it is.

Got done recapping the deflection circuits. I replaced all 17 caps in savon pats kit and swapped the values he suggests with his kit (someone posted the cap info on reddit) and also swapped out that big 220uf 160v cap by the flyback and all the other caps directly near the flyback.

She fired up, i hear the HV whine,degaus, hear a loud pop everytime I fire it on which im not sure what it is, maybe ill clean under the anode cap again..... Anyway, I get a "no sync" message that fades away after a few seconds.... Tried to connect a snes through svideo but cant change inputs. Seems none of the front panel buttons work.
Ive read if the remote led indicator is on then it could be locked into a user preset which disables the front buttons but the remote indicator light is not lit, cant bring up the menu, change source or anything.
Any ideas?

https://ibb.co/j4WMGyH

Told you: it's always caps (until it's not).
The control panel issue is rare and unheard of, I bet it's something silly like poor solder joints somewhere. I know it's a pain to disassemble the front panel, but inspect it to see if there's any obvious issue.

[deezdrama]

Told you: it's always caps (until it's not).
The control panel issue is rare and unheard of, I bet it's something silly like poor solder joints somewhere. I know it's a pain to disassemble the front panel, but inspect it to see if there's any obvious issue.

I dreaded getting to the front panel board but it wasnt that bad.... I just had to remove the bottom tray that the chassis board sits on.
I got the front panel H board out. It looks pristine and literally is just a board with the buttons, some resistors, and the pot knobs..... Not much to go wrong here. All the connections were solid. No idea what to look for now

Edit....
Started a thread with pics...
viewtopic.php?f=6&t=70544&p=1503382#p1503382

[NewSchoolBoxer]

I recently acquired an PVM-14M4U that had, well, still has technically, the red/orange tally of death. It seems to be a known problem on these models which can be caused by different reasons.
In my case however all it took to make it work perfectly again was to blow hot air on the main circuit board. Now, I've ruled out the power supply and the other boards, so there is some issue on the main board.

So I ask this question... what could a relatively short stream of hot air affect on the board to bring it back to life? Could it be a cold solder joint? Or perhaps the infamous capacitors? Has anyone here heard of something like this or had a similar experience in electronics in general? Im looking for a more permanent fix.

I had a notoriously faulty Android G3 or G4 phone from 5 years ago where it stopped turning on after 6 months. Throwing it in the freezer and pulling out would fix it for a few minutes. I had better success baking the PCB in the oven to restore functionality for a day or two - enough to backup my texts and pictures. Idea is to reflow the solder joints for a temporary fix. In your case the heat reduces the electrolytic capacitor ESR, temporarily. Not that I would have thought of either idea on my own.

I'm impressed by your follow up work and using a proper ESR meter to showing the reading were sky high. Visual inspection isn't enough to detect caps that should be replaced.

Good point about caps near heatsinks suffering the most. Every additional 10°C towards the upper limit cuts an electrolytic capacitor's lifespan in half and ages non-electrolytics to some extent.

[Housematt]

Extreme thread necro - wanted to say a huge "thank you" to @tongshadow for this tip. Was doing a brain transplant on for an M4 with a bad board but a good tube with an M4 good(?) board and a bad tube. Was working - refused to work in the workshop - 5 mins with the hairdryer and it was back in action. Now for the long, long recap road...

But the point is, thank you! I would never have thought to do this otherwise.

[tongshadow]

Glad it was useful
These machines are not complex, but due to the sheer amount of components and capacitors it can be hard to track down an issue. Sometimes unconventional diagnosis/testing is the way to go.

[Analogized]

what happens is that something on the A Board is causing the 15V line to drop to only 12V, and consequently the 12V line drops to 10V.

Where were you observing low 12V? I have a 1953MD that is exhibiting a similar issue, although idk if hot air is the fix, as I haven't tried that!

[Analogized]

Also, do you remember if you were getting HV to the tube before the issue was fixed? Of the two I have, one does and one doesn’t.

[tongshadow]

Where were you observing low 12V?

Right on the Power Supply 15V pin. And no, it didnt have high voltage at all, only after heating up the capacitors, causing them to partially work and let the monitor start up.

[Analogized]

Where were you observing low 12V?

Right on the Power Supply 15V pin. And no, it didnt have high voltage at all, only after heating up the capacitors, causing them to partially work and let the monitor start up.

Thanks for the response! Much appreciated! However, I’m sorry to say I’m a bit confused. You say the PSU was fine, and produced the voltages perfectly, and the voltage discrepancy was observed on the A board, no? Am I missing something?

[tongshadow]

You say the PSU was fine, and produced the voltages perfectly

When the cable to the main board (A Board) was disconnected, I got 15V. Like this:
https://i.imgur.com/qAOZ1Yo.jpeg

So when I used the same point as a reference, with the cable connected to the main board, I got lower voltages.

Maybe my post was a little confusing.