Red Lines on VFD - DVD Player Stopped Working - Page 1
Forum section: electronics / repair

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 24, 2021, 06:54:36 pm
content: I have a weird issue here.I have a HDMI DVD player I have had since 2008. It is a Silvercrest brand player (not sure of model until I pull it out the cabinet) which I got from Lidl in 2008. Up until last night is has been a great player!I was watching a movie last night and all of a sudden the HDMI signal just dropped. I looked at the players display and it had 'frozen'. The time counter has just stopped but the pause icon was not illuminated.I tried turning it off with the remote but it would not respond. So I unplugged it from the mains and left it for 1 minute before connecting it back up.When it connected back up the display looked like this (see picture). In this state the unit is dead. it will not respond or do anything at all.The display is getting very toasty warm in this state so I powered it down right away to avoid further damage.Now I have done some research and Youtube has taught me that these lines are the Cathode filaments of the Vaccum Fluorescent Display.Now in normal operation they don't glow red so my instinct says that perhaps this might be a power supply issue?? Maybe bad capacitors?Has anyone encountered a similar issue before? And if so what might be the cause here.

author: Gyro
author_rank: Super Contributor
timestamp: November 24, 2021, 07:13:28 pm
content: Yes, that's a severe overvoltage on the VFD filaments. The worry is that the other supply rails from the PSU have gone up by a similar amount, which would almost certainly be fatal to the ICs.I don't think such a fault would be down to a capacitor problem, they tend to be more subtly, causing unreliable operation, at least initially. This looks like a sudden loss of PSU regulation, maybe a semiconductor failure in the feedback loop.It's hard to say more without knowing what has happened to the other supply rails. The player is clearly well out of warranty, but I don't know how confident / competent you feel about working on mains powered equipment.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 24, 2021, 07:21:22 pm
content: Quote from: Gyro on November 24, 2021, 07:13:28 pmI am hoping it has not fried the ICsLooks like I will be pulling the player out. I will take some photos of the inside.I guess a good first step is to see if the power supply can be disconnected and I will test the voltages of the outputs rails.Yes I am more than confident/competent at working on mains powered equipment and well aware of the potential dangers.

author: Gyro
author_rank: Super Contributor
timestamp: November 24, 2021, 07:27:02 pm
content: That looks like a good first step (isolate and measure) then. Best case would be a fault just on the VFD filament supply, but the fact that all other functionality ceased at the same time seems a bad omen.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 24, 2021, 07:42:34 pm
content: Quote from: Gyro on November 24, 2021, 07:27:02 pmI knowI really hope it is something simple. Would be a shame as this player is great.Will post back in the next few days with my findings and photos.There was no magic smoke or anything with a funky smell. But even so could be serious.I am assuming that the VFD filaments would run on a high negative DC voltage?I have never really worked with VFDs before. To me it seems like the work just like a valve.

author: Gyro
author_rank: Super Contributor
timestamp: November 24, 2021, 09:09:20 pm
content: The VFD filaments normally run on some form of AC - traditionally from the mains transformer, but in these SMPS days probably from a none rectified winding on the SMPS(?) or an H-bridge driver.The VFD is a valve in all meaningful ways. The filaments are directly heated cathodes so, if fed from DC, the brightness of the display would vary from one end to the other. The filament is also biassed negative (by something like -25V) relative to the display segments and grids. This allows these to work at roughly logic levels.One random thought... The filament bridge drive might be controlled by outputs from the micro, but even stopping the bridge completely wouldn't affect the temperature of the filaments so it still comes back to PSU.Good luck with the detective work, hopefully we can provide help after measurements and photos.

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 24, 2021, 09:35:19 pm
content: Since it seems to have lost regulation if you do power the PSU disconnected from the rest for troubleshooting beware that it doesn't pop an electrolytic at your face.

author: commongrounder
author_rank: Frequent Contributor
timestamp: November 24, 2021, 09:40:02 pm
content: I’ve seen this on units that came through my service facility. Typical switching power supplies in these use one of the output supply rails (usually the +5v or +12v) to drive the regulation feedback loop to the “hot” side of the supply through an option-isolator. The problems arise when the caps go bad on that rail. The voltage drops, which drops the feedback, the hot side drive increases in an attempt to bring it back to normal. The result is all of the other rails go completely over voltage. Now, well designed power supplies have zener clamps on each output to prevent damage to the load devices. The question is what happened to your unit? My guess is recapping the power supply will restore proper voltages, and you can see if the chips survived. Good luck!

author: TheBay
author_rank: Unknown
timestamp: November 24, 2021, 09:52:39 pm
content: I'd say there is a good chance it's capacitor related in the SMPSU, if you're lucky you may actually end up with a brighter VFD after this fault as the VFD cathode filaments have been run for a little bit with too much voltage.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 24, 2021, 10:11:11 pm
content: Ok this is all good stuff! Thank you.I will see if the power supply can be disconnected and check the output voltages.I have an ESR meter. I will check all the power supply capacitors and see what I find.

author: Gyro
author_rank: Super Contributor
timestamp: November 24, 2021, 10:45:27 pm
content: Note that if an electrolytic cap has suddenly gone short circuit due to overvoltage, it might look as if it just has a very low ESR. It's always worth checking on a DMM DC ohms range too - or check that the related PSU output rail isn't shorted beforehand.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 24, 2021, 11:00:41 pm
content: Ah yes good call. Will bear that in mind, thanks!

author: DaveG8KBV
author_rank: Newbie
timestamp: November 26, 2021, 05:47:29 pm
content: I sort of wonder if the initial symptom, of the HDMI signal quitting and the display freezing (but no red lines?) indicates a shorted decoupling cap on a digital board somewhere. Or failed unobtanium IC.But concur with the comment that pulling the main regulated output of a cheap multi rail SMPS could cause the other rails to run high. But, I've not personally seen VFD filaments run direct from the main SMPS. More usually from an onboard inverter that also provides the -25(ish) voltage. But, there again, I rarely work on "consumer" stuff.You may find, when disconnecting the PSU from the rest of it, that the main rail (+5 or +3.3) is fine, but the others are now low. That would indicate the PSU may be OK. (Check by loading the main rail to something like half an Amp, and see if the others come back, so long as that main rail doesn't collapse under any load, however small, in that case the PSU is likely duff.SMD Tant' caps are prone to suddenly going short cct, especially those placed across a power rail. (Don't ask how I know..) They don't tolerate surges too well either.Even if you can't fix it, you'll learn a load about fault finding, that will do you well in the future.Good luck.Dave 'kbv.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 27, 2021, 03:42:09 pm
content: OK so here is my player. I cannot see a model no. on it anywhere mind you.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 27, 2021, 03:45:03 pm
content: Here is the inside.First thing I see is a swollen capacitor!

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 27, 2021, 03:56:00 pm
content: This is the power supply board.I will check the output voltages of this board next and post back.

author: commongrounder
author_rank: Frequent Contributor
timestamp: November 27, 2021, 03:59:20 pm
content: Quote from: paul_g_787 on November 27, 2021, 03:45:03 pmYup!

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 27, 2021, 04:07:06 pm
content: On this connector I have the following measurements.Between the two pins marked AC3.5V I have 6.0V DC and 0V ACAll the following measurements taken with respect to pin marked GND. I also took the measurements with the probes reversed and have the same readings.-24V Pin I have -45V DC and 0VAC - This is not good at all!5V I have 4.99V DC and 0V AC - Perfect here5V-ST I have 4.99V DC and 0V AC - This seems good I thinkSTBY I have 6.0V DC and 2.25V AC - Is this showing a high ripple current??

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 27, 2021, 04:11:13 pm
content: And on this other connector I have the following measurements.Both 5V pins 4.99V DC and 0V AC+12 V Pin is at +24V DC and 0V AC-12 V Pin is at -24V DC and 0V AC

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 27, 2021, 04:22:17 pm
content: I notice on the primary, R5 is a bit toasty looking.It appears to measure 10KIt is a bit hard to tell on the colour bands though.I also tested the diodes here for good measure and they are all fine.

author: TheBay
author_rank: Unknown
timestamp: November 27, 2021, 04:30:02 pm
content: No point checking voltages until the faulty capacitors are replaced.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 27, 2021, 04:34:51 pm
content: Just checked all the semiconductors on the secondary.There are no direct shorts on any of these which is a good sign!!Yes, my next step is to change the capacitor that is obviously faulty. And I will check the ESR of all the others with my MESR-100 meter.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 27, 2021, 04:51:31 pm
content: the swollen capacitor is a 2200µF 10V and is measuring 6Ω ESR. So definitely dead by the look of it. I will replace it.The one next to it is 1000µF 10 V and has a 0.5Ω ESR which my meter says is dead. I will change this also.Those are the two blue capacitors in the middle. I will change these right away and see what happens.The other capacitors with red dots on are right at the top threshold of their ESR but I think they are still OK. I will leave these in for now.The capacitors I haven't marked have good ESR.

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 27, 2021, 05:39:03 pm
content: It looks very similar to some players made by Peekton, then again a lot of these cheap players are similar regardless of the name on them.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 27, 2021, 05:54:24 pm
content: OK, so I have found some capacitors in my spare parts to replace the two faulty ones. These have been soldered in.I also removed R5 and had a look in the bright light. It is definitely Brown / Black / Something??It measures 9.996K so I am convinced it must be 10K as this is so close. I have soldered in a new 10k 0.25W resistor. The original was 0.125W. Not sure what caused it to burn up though..I am going to plug it in now and see if there are any explosions.If there are no explosions I will measure the output voltages again.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 27, 2021, 06:09:49 pm
content: OK, voltages as follows.0VAC / 3.6V DC between the two 3.5V AC pinsSTBY is at 5.87V DC and 2.12V ACI am confused by these two...-24V is at -24.5V5v-ST is at 4.95V+5V is now at 5.0V DC+12V is at +12.6V DC-12V is now at -12.5V!! DCNo AC measurements to be seen on these DC rails.I reckon it is time to connect it back up and see what happens.?

author: james_s
author_rank: Super Contributor
timestamp: November 27, 2021, 06:27:52 pm
content: 3.6V DC on the 3.5V AC suggests that the earlier hypothesis is correct, that the AC filament voltage is developed by the microcontroller or some other circuit switching a H-bridge. For some reason that is not happening so the output is just stuck at DC. You might see if you can find the microcontroller and check for voltage at that, I would expect it to run from 3.3V although it may be 5V. Check the reset pin if you can locate it and also the clock. The tricky thing about servicing stuff like this is you generally don't have a schematic so there is a lot of guessing involved.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 27, 2021, 06:45:11 pm
content: OK so I connected the board up to the player and when you power on the device the 3.6DC Voltage goes away and a 3.6V AC voltage appears..When you put the player in standby mode this reverts.So I would guess that the main board tells the power supply to start switching?Regardless, good news!! The player powers up, the disc spins and the VFD is un-harmed and working greatI am going to pop the lid back on an connect to the TV and see if I get a picture.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 27, 2021, 07:04:16 pm
content: Some very good news! It is working just fineThe VFD does appear to be a little brighter than I remember. But all appears to be well.I will pop it open again in a few months and perhaps change those other slightly high ESR capacitors.I have certainly learned a bit more about switch mode supplies from this and also about how VFDs work.

author: Gyro
author_rank: Super Contributor
timestamp: November 27, 2021, 08:01:40 pm
content: Well that was a rather better than expected result!The amount of wiring might be a little excessive (it's very modular) but it looks pretty well constructed. I can't help noticing that large heavy slotted ferrite on the wide ribbon going to the front panel. It is glued to the PSU output ribbon very close to the srbp material PCB, it's just possible that it might have encouraged a cracked trace. It's been working for a very long time since it was shipped though.I guess keep and eye on it and enjoy meantime.

author: paul_g_787
author_rank: Frequent Contributor
timestamp: November 27, 2021, 09:04:11 pm
content: The ribbon with the ferrite on it is going to the SD / CF card reader / USB port on the front panel.No cracked traces as far as I can tell.