Barclay PINSentry dead, suspect SMD SOT-23-5 LDO F50 - Page 1
Forum section: electronics / repair

author: Lomax
author_rank: Frequent Contributor
timestamp: August 14, 2025, 05:48:44 pm
content: I'm currently abroad and was horrified to find that my Barclays PINSentry OTP generating gadget has died, which leaves me without access to moneyThe device is completely dead, with no sign of life whatsoever. It looks like the LDO has been killed by corrosion. I don't have the equipment to try a repair, but I'm thinking I could solder in a USB power cable, positive to the cap in the top right in the photo, and negative to the first battery holder's negative (it runs on 4xLR44). But I'm a little hesitant: 5V sounds a lot for a device like this, especially from just four 1.5V batteries. Could the F50 LDO actually be a 3v3 part?

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 14, 2025, 06:42:09 pm
content: no warranty, but F50 could match to the SP6201ER-L series by Exarhttps://www.alldatasheetde.com/datasheet-pdf/view/926652/EXAR/SP6201ER-L.htmlSo it should be an 5V LDO, as the marking code in table states (page 5)

author: floobydust
author_rank: Super Contributor
timestamp: August 14, 2025, 06:55:34 pm
content: The board looks like water ingress from the PCB hole (rust?) and flux residue, dirty assembly courtesy the gutters of guangdong.U4 "F50" has high impedance 1MEG R8 so flux on that IC pin might keep it off.Also the 32kHz crystal will not take any corrosion between its leads. These parts area sensitive to residue on the board.Lowest risk, try a toothpick to knock off especially on any blue or green residues on the IC pins, or the crystal's pins. Especially between them.I would scrape that, see if it comes alive.Otherwise, clean off the board with cotton swabs and IPA.It will reboot the board, assuming it's always powered? I'm not sure if anything is stored in volatile memory on this. Or if it goes to deep sleep when off.

author: Lomax
author_rank: Frequent Contributor
timestamp: August 14, 2025, 09:55:40 pm
content: Quote from: Uunoctium on August 14, 2025, 06:42:09 pmThanks, yes,I found a couple different SOT-23-5 LDOs and DC converters with F50 in the name, some which had it as package marking. Annoyingly this is rarely mentioned in the datasheet though. It would seem reasonable to assume it's a 5V part, but I'd prefer not to chance on it.Quote from: floobydust on August 14, 2025, 06:55:34 pmThanks, I have cleaned the PCB with IPA and an old toothbrush. Looks pretty ok now actually. No signs of corrosion around the crystal. The damn thing is still dead as a doornail though

author: floobydust
author_rank: Super Contributor
timestamp: August 14, 2025, 10:58:24 pm
content: Need to poke around with a multimeter and see if there is power getting into the IC or if it is enabled. LR44 batttery/holder might have corrosion too.

author: Lomax
author_rank: Frequent Contributor
timestamp: August 15, 2025, 09:27:34 am
content: Quote from: floobydust on August 14, 2025, 10:58:24 pmBattery holders are fine, no corrosion or anything. Unfortunately there's no way to access the PCB while the batteries are installed; the back shell is what holds them in place. But I've soldered a USB power lead to the negative on the first battery and positive on the last, measuring 5.2V on the input to the LDO (pin 1), but zip/zilch/nada on the output (pin 5). Not sure that's enough voltage though, since I haven't been able to determine exactly which LDO this is. The real question is though: do I dare to move the positive lead from the USB to the positive side of the output cap?

author: Lomax
author_rank: Frequent Contributor
timestamp: August 15, 2025, 09:42:33 am
content: Actually it appears to be hiccuping; if I measure the output voltage from the LDO while holding the startup switch closed (normally triggered by the insertion of a card), the voltage briefly jumps to just above 2V every second or so. No shorted caps found, resistance between negative & positive around 500kΩ, also with the startup switch closed.

author: Lomax
author_rank: Frequent Contributor
timestamp: August 15, 2025, 11:56:08 am
content: Actually, scratch that; having soldered a wire to the positive side of the output cap to make it easier to measure things I'm not seeing any hiccuping any more - I think it was just my third hand not being steady enough when I was trying to hold the meter probe in place while operating the start-up switch. What I do see is a very brief voltage spike of just over 2V when the start-up switch is closed, immediately dropping to ~0. I've also carefully cleaned the whole PCB with IPA and a toothbrush - no difference.

author: Lomax
author_rank: Frequent Contributor
timestamp: August 15, 2025, 12:07:01 pm
content: Having soldered a wire to the positive side of the LDO's output capacitor also allows me to check the voltage when a card is inserted (which covers the PCB), just to check if the presence of a card chip might have something to do with it - but the behaviour is the same. I'm pretty sure that LDO is dead. But what output voltage did it provide? This remains question #1.

author: Lomax
author_rank: Frequent Contributor
timestamp: August 15, 2025, 12:22:51 pm
content: I think I might have found the part! Package matches, pinout matches (including pin 4 being used), andthe marking matches(if it's a 5V LDO).https://www.mouser.com/datasheet/2/146/exars02414_1-2267116.pdf

author: Lomax
author_rank: Frequent Contributor
timestamp: August 15, 2025, 01:29:48 pm
content: With nothing to lose I fed 5V into the other side of the LDO, and the device came to life! One row of pixels missing, which isn't a problem, but it's stuck with "battery low" showing on the display and not responding to any keys, despite having an old expired Barclays card inserted. Figured there might be some battery voltage detection going on before the LDO so tried putting the back on and inserting four known good batteries as well as the 5V from USB - but that changed nothing. Hmmm. Any ideas?

author: Lomax
author_rank: Frequent Contributor
timestamp: August 15, 2025, 01:40:14 pm
content: Perhaps I need to ground pin 4, on the other side of the 1MΩ resistor to pin 4? This is the "VOUTgood" pin, which I imagine the MCU is watching...

author: chilternview
author_rank: Frequent Contributor
timestamp: August 15, 2025, 01:55:02 pm
content: There's probably no harm grounding pin 4, it's worth a try.Sommewhere I have one of those in a drawer. Never tried opening it up!

author: tom66
author_rank: Super Contributor
timestamp: August 15, 2025, 01:57:55 pm
content: Using 'PG' to detect battery low is a trick I've used in the past so it makes sense. It will be grounded when the battery is 'good' - i.e. the regulator is regulating correctly. 4 x LR44 cells will measure around 6.4V when completely fresh, and about 4.0V when completely dead, so they're throwing away a fair bit of life if they cut out around ~5.2V... but my guess is they don't really care given the product probably lasts long enough before something else on it fails.I definitely have an old Barclays smart pad somewhere which they sent to me to register the phone 'app'. It has been used precisely zero times since then, and is effectively e-waste, but I'd be happy to make some measurements on my board if it helps you.

author: Lomax
author_rank: Frequent Contributor
timestamp: August 15, 2025, 02:22:24 pm
content: Thanks guys. I really had high hopes that would be it - it seems the MCU is running, since I'm getting the "battery low" message, so it's gotta be pretty close - but I'm sorry to say grounding pin 4 made no difference at allAlso tried with batteries installed, in addition to USB power, same thing, "battery low". What else could it be?

author: Lomax
author_rank: Frequent Contributor
timestamp: August 15, 2025, 03:27:16 pm
content: Quote from: Uunoctium on August 14, 2025, 06:42:09 pmYes. I think that's the one! I stumbled upon it today, having forgotten that was the part you had suggested from the startQuote from: Lomax on August 15, 2025, 12:22:51 pm

author: nali
author_rank: Frequent Contributor
timestamp: August 15, 2025, 05:20:25 pm
content: I've got one of those been laying around for years so I hooked it up out of curiosity.LDO is defiantly 5V, activated by the card contact switch. I didn't measure the LDO output but varying the supply it drops out at ~4.9V. I did notice that turning the supply back up didn't clear the LOW BATTERY until power was removed & reapplied. If power is OK it shows CARD NOT RESPONDING.As a side note I'm really surprised there's no anti-tamper mechanism - but it appears there isn't.

author: tom66
author_rank: Super Contributor
timestamp: August 15, 2025, 11:39:28 pm
content: There's probably no need for an anti-tamper mechanism because it relies on the cardholder knowing one secret (their PIN or other key) and this device is only attesting the existence of the card and the cardholder being in the same place. Any tampering would still require the other two factors: the PIN, and the card; and it would make the device more expensive. The blobbed chip is almost certainly a crypto-chip of some kind, but probably has minimal if any secrets embedded into it. I'd be surprised if these devices are customised at all, and they should work with any card provided you have the PIN.OP, did you try shorting the PG pin to ground permanently, or are you just shorting it after it boots?

author: amyk
author_rank: Super Contributor
timestamp: August 16, 2025, 07:15:22 am
content: The real crypto (and secret) is on the processor in the card you insert. This device just contains a simple MCU that interacts with the card.

author: drhex
author_rank: Regular Contributor
timestamp: August 16, 2025, 07:48:43 am
content: Where are you? I have a few of these readers popping about (think they are the same thing across banks). Could mail one.

author: Lomax
author_rank: Frequent Contributor
timestamp: August 20, 2025, 09:19:07 am
content: Thanks everyone! The solution arrived today, in the form of a "Gemalto" pin sentry device, which works with my card & bank. £5 delivered. Back in business!