I've got this monitor for free as previous owner gave up on fixing it.
Symptoms: monitor works fine at first look, but after hour or so it may randomly turn off or start showing image with weird colors (e.g. missing one color entirely). OSD menu has often random minor artifacts. It cannot be turned on again using ON/OFF button but with powered off entirely (detaching power cable) for few minutes it starts working correctly again for a random time. Sometimes image might get really weird:
From the posts on few forums this is common issue with this model and also with larger XB2374HDS and E2475HDS / B2475HDS. Two possible problems are listed: failure of NOVATEK NT68677UMFG chip (scaler) and failure of serial EEPROM (A25L020). Some suggested that main chips are just faulty and need replacement, but my plan for now is just trying to lower it temperature using radiator from old Pentium 4 motherboard north bridge.
After testing for a few days this radiator seems to be helping, not fixing all problems (like not powering on after signal going down and then up) but reducing them significantly (hours of work but still need to cut down the power once or twice per day) - this might be just coincidental.
PAM8007 - class D power amplifier, 2 x 1.5W @ 4Ohm, 10% THD, 5V supply.
Audio quality is very poor as nothing separates the front and the back of the speaker. Perhaps some piece of plastic is missing from this unit? Otherwise this would be just poor design - sacrificing audio quality for like a dollar.
Monitor is using PWM for brightness control - it is working with 240Hz frequency right after brightness is reduced below 100%.
I've changed scaler chip for new one (from 2016) bought on ebay for ~$4. Although I've used hot air old one was rather hard to desolder. Also, despite used some protecting aluminum foil I've blown away 2 or 3 0402 SMD components near the chip - be careful when setting air flow.
Replacing scaler did not seem to make difference - monitor is still randomly shuts off, so my next planned step is replacing Flash chip. I have now new chip soldered and I've added piece of 3M thermal tape and small radiator just in case, but I think replacing Novatek was not necessary.
Update: Pm25LD020 finally arrived ($1.50 for 5 pieces) and then I realized I have no programmer for these low voltage chips (pickit2 with flashrom did not work for me), so I also ordered CH341A-based flash programmer ($2.50).
After desoldering original A25L020 I wasn't able to read anything making sense from it - it is possible I have overheated it, but I've used firmware from
https://www.elektroda.pl/rtvforum/viewtopic.php?p=15640144#15640144 (iiyama ple 2274hds-b2 25l020.bin) and it seems to work. For programming I was using
CH341A.
I don't see any problems with monitor at the moment.
This seems to be frequent problem with this model, but if you have to spend money to fix it keep in mind that this is not top of the line device - vertical viewing angles are pretty poor, PWM frequency is low (240Hz), speakers are just disgusting.
LED driver: OZ9998BGN, controlling 4 LED strings, up to 160mA per string, external PWM dimming input. My guess is that PWM frequency is controlled by scaler firmware thus might be not possible to change.
(low quality schematic comes directly from datasheet)
LD7576AGR - power supply controller
SMK0965 - N-channel MOSFET, 650V, 9A.
SP1060 - dual Schottky diode, 60V, 5A per leg
APM8005 - dual N-channel MOSFET, near LED driver chip
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ReplyDeleteHello, same problem here, and solved, really easy, it was the two or one of the two (I refreshed both) PowerFET choppers on the power
ReplyDeleteboard that have dried up thermal paste between them and their cooling fin resulting in overheating and consequent thermal shutdown, not
destructing in my case.
remedy:
-open the screen with a blunt blade prying in between the plastic shell and plastic ring (start at the powerindicator LED, underside of
the screen), be carefull not to damage the screenmatrix with your tool
-disconnect the wires and flatconnector to the central metal case
-there is some aluminium foil, you have to break it, I didn't replace those afterwards, is for better EMC compliance
-lift the central metalcase
-disconnect the powerwires bundle connector from the power board to the motherboard
-disconnect the power board (3screws), lift it of the metal case.
-there are two powerFETs with cooling fin in aluminium
-unscrew the two screws that connect the chopper PowerFETS to their cooling fin
-carefully pry the FETs a millimeter or two away from their cooling fin
-scrape off old thermal paste in between
-reapply a layer of half a millimeter good thermal paste with a small blunt blade tool (Arctic Silver, Amasan T12, ...)
-reconnect tightly the cooling fin to the PowerFETs with the screws.
pack up everything and ready is the screen, for another couple of years
You could make the design better by applying mica plates as replacing the thermal compound (the mica plate goes between the
powertransistor and the cooling fin isolateing one from the other electrically, while letting the heat through) and drilling a somewhat
wider hole in the cooling fins, and replacing the screw with a bolt and nut connection with a lock nut(all metric M3 size), making sure
the PowerFET is tightly pulled against the aluminium plate at all time.
Thanks for the comment. I've added few power supply board photos and in my case connections to radiators seem good enough, so my next bet is replacing SPI Flash chip (changing scaler chip did not help).
DeleteI can now confirm that replacing SPI FLASH (programmed with CH341A) fixed issue for me.
DeleteHi,
ReplyDeleteI fixed a PLB2475HDS-B1monitor thanks to the reprogramming of the 25l020 eeprom.
Initially, the HDMI input was not working, the input signal was not recognized. Some times, the software in the scaler crashed, to reset everything the only way was to leave the monitor unplugged for a couple of minutes.
I also added some filter caps on the 5v and 12v power supply to avoid potential spikes.
First of all, thank you for this, it saved my monitor it seems.
ReplyDeleteI would like to add my 2 cents, although this topic might be already old.
I had the same issue on my Iiyama ProLite B2475HDS, the monitor would turn off after some time.
I have investigated this and identified the problem to be the above mentioned EEPROM, but what is interesting is that the problem is kind of a 2 stage one. When the A25L020 would heat up the monitor would either shut off until it cooled down, or lag out and wouldnt even turn off etc.
I really did intensive testing regarding this heat issue and i can confirm it with 99,9% certainty. For more than 2hrs I would try to heat up separate sections of the 2 circuit boards inside the monitor. The only thing that would react to any amount of heat was the A25L020. Any other element was heated extensively but nothing happened.
But when I only touched the A25L020 for just 2sec with the soldering iron, the monitor would shut down. After a blow of cold air from compressor (thus cooling the eeprom) the monitor would turn ON again. If no cooling was done, the monitor would not turn on for longer.
This in my opinion really localized the problem to the A25L020. Now the interesting part is, that the heat does not come from the eeprom itself, but rather from the Novatec NT68677UMFG. This heat is in my opinion perfectly normal, and so I decided NOT to replace this chip.
One solution would be to add a heatsink to the NT68677UMFG (or maybe even a small fan inside the casing of the monitor) but this does not solve the problem, it only "avoids" it a bit.
Thanks to your blog I decided to replace A25L020 with Pm25LD020. I had a bit of issues with writing the firmware on it (I couldnt remove the write protection). Thankfuly I bought a set of 10 Pm25LD020 because on first 2 I couldnt remove the write protection, on the third one I removed it but the firmware I wrote on it was then read differently than the original etc. The 4th chip was OK, I removed the write protection, smacked the firmware on it and even when reading it back I couldnt see any issues.
I then replaced the working eeprom on the circuit board of the monitor, and voila, so far so good. Please keep your fingers crossed that this isnt just a fluke and that it keeps working (thanks :D ).
If any other advice is needed I can try to help the best I can. Im no electronics repair guy, and this was a big challenge for me, that is why im willing to help others who may strugle - if I will be able to ofcourse...