Just a quick teardown this month! This is an industrial RS-232/RS-485 to Ethernet serial converter.Not much to say about the outside of the unit, there’s the DB-9 connector for the 232 interface, and Phoenix connector blocks for the 422/485 interface. The main power input, and the Ethernet jack are on the other side.
PCB
Under the hood, there’s a pretty densely populated board. The brains of the operation is a IP210T Serial to Ethernet SoC with A/D Converter. This is an 8051 based core, wuth 10/100 MAC. No flash memory here either, only 64KB of OTP EPROM. On the left there’s a few bus transceivers to interface the serial ports, along with some glue logic. At the top we have the Ethernet magnetics, configuration EEPROM for the SoC & a trio of indicator LEDs.
Power supplies are dealt with via an LM2576-3.3 DC-DC buck converter, providing the main 3.3v rail for the logic.
Being in technology for a long time, I have seen my fair share of disk failures. However I have never seen a single instance where SMART has issued a sufficient warning to backup any data on a failing disk. The following is an example of this in action.
Toshiba MQ01ABD050
Here is a 2.5″ Toshiba MQ01ABD050 500GB disk drive. This unit was made in 2014, but has a very low hour count of ~8 months, with only ~5 months of the heads being loaded onto the platters, since it has been used to store offline files. This disk was working perfectly the last time it was plugged in a few weeks ago, but today within seconds of starting to transfer data, it began slowing down, then stopped entirely. A quick look at the SMART stats showed over 4000 reallocated sectors, so a full scan was initiated.
SMART Test Failure
After the couple of hours an extended test takes, the firmware managed to find a total of 16,376 bad sectors, of which 10K+ were still pending reallocation. Just after the test finished, the disk began making the usual clicking sound of the head actuator losing lock on the servo tracks. Yet SMART was still insisting that the disk was OK! In total about 3 hours between first power up & the disk failing entirely. This is possibly the most sudden failure of a disk I’ve seen so far, but SMART didn’t even twig from the huge number of sector reallocations that something was amiss. I don’t believe the platters are at fault here, it’s most likely to be either a head fault or preamp failure, as I don’t think platters can catastrophically fail this quickly. I expected SMART to at least flag that the drive was in a bad state once it’s self-test completed, but nope.
Internals
After pulling the lid on this disk, to see if there’s any evidence of a head crashing into a platter, there’s nothing – at least on a macroscopic scale, the single platter is pristine. I’ve seen disks crash to the point where the coating has been scrubbed from the platters so thoroughly that they’ve been returned to the glass discs they started off as, with the enclosure packed full of fine black powder that used to be data layer, but there’s no indication of mechanical failure here. Electronic failure is looking very likely.
Clearly, relying on SMART to alert when a disk is about to take a dive is an unwise idea, replacing drives after a set period is much better insurance if they are used for critical applications. Of course, current backups is always a good idea, no matter the age of drive.
I was recently given a pretty nice LED backlit 1080p LG monitor, with the instruction that it wouldn’t power on correctly. The monitor would power on as far as the standby light, but when fully powered on, would flash the backlight momentarily then shut down. A power supply issue was immediately suspected.
LCD Logic Board
I popped the covers off the monitor itself first, thinking that it was an electrolytic gone bad in the backlight DC-DC converter. Not to mention the fact that cracking into a wall-wart type of PSU is only occasionally possible without the use of anger & large hammers. (Cracking the glue with the handle of a screwdriver doesn’t work so well when the factory went a bit nuts with the glue/ultrasonic welder). As can be seen in the photo, there’s not much inside these monitors, the logic is a single-chip solution, the rest of the PCB is dedicated to supplying the power rails for the various circuits. On the left is the power input & the DC-DC converter for the backlight, along with the DC-DC converter supplying the logic circuits. None of the capacitors here are damaged, everything looks good.
I then measured the output of the PSU, which under no load was the correct 19v DC. However applying any load caused the output voltage to drop like a proverbial brick. Applying a full load of 1.3A saw the output voltage drop so severely that the PSU tripped on it’s UVLO.
200mA Load
At 200mA of load the factory PSU is already dropping to 18v, with a 5.3kHz switching frequency appearing.
500mA Load
At higher load the frequency increases to 11.5kHz & the output voltage has dropped to 11.86v!
750mA Load
750mA was as high as I could make the supply go without it tripping itself out – the UVLO circuit trips at 9v. 12.6kHz is now riding on the severely low DC at this point.
PSU Ratings
The power supply is supposed to be rated at 1.3A at 19v, however with this fault it’s getting nowhere near that. The LG brand is on this PSU but it’s contracted out to Shenzen Honor Electric Co. Ltd.
Output Electrolytic
Here’s the problem with this PSU. The output electrolytic has ballooned. I don’t have an ESR tester, but this cap has gone way past it’s sell-by date. It’s position right next to the heatsink with the output rectifier diodes has probably cooked it. The PSU isn’t that badly built for a Chinese one – there’s plenty of creepage distance on the PCB & even a couple of isolation slots.
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