Missing display segments on power supply

[Brad808]

I have a power supply (power ten 3300 series) that has some weirdness happening with the voltage and current display segments. I have a couple of identical power supplies so I've been able to narrow down my issue a bit by swapping some parts. Unfortunately I can't find a copy of the schematic. I'm sure I'll be able to track down the issue by swapping parts, but if any of you here have any idea of what I should be looking for I'm more than happy to take advice.

The current display was showing random digits and missing segments like this;

The voltage display was showing the correct voltage but for some reason now it is 13 or 14v above what it should be and the pot isn't able to adjust it out.

Here is a description of the board operation:

Here is some photos of the board:
https://imgur.com/a/qJgmUAG




Couple of things I've done:

- swapped the whole display board to another unit and the problem is definitely on the display board, not the main board
- retouched all solder joints on the board (minus the sockets underneath the LCD which I'll do tonight)
- swapped the two AD converters in u3 and u4 with ones from a working board
- verified the +/- 5v regulators are working.

That's about as far as I've gotten. I'll keep working away at swapping parts and testing individual components, but any help is appreciated.

[coromonadalix]

you could have some bad contacts with the pin vs the glass substrate  ?  mechanical failure

[wraper]

Looks like faulty display. Sometimes adhesive delaminates and metal terminals no longer have continuity with the contacts on glass. Looks like a fairly common off the shelf LCD like this https://www.aliexpress.com/item/32920933993.html

[floobydust]

Yes it sounds like you've tried everything leaving a failed LCD display. It might have a hairline crack open-circuiting the segment traces on the glass. You can poke it and apply a little pressure here and there to see if anything changes. An air bubble usually makes for an odd outline on the segments. With old 80-90's LCD displays I find some kind of tin whiskers form inside at the electrodes.
The part number is written on the LCD backside, so you'd have to pull it.

[Brad808]

So tonight I was able to fix the voltage issue (I didn't realize the how the LCD jumpers were set so easy correction there).

I was able to confirm the display itself is bad by swapping them around (bit of a pain to be honest).

This is the model number of the display. I really don't know anything about them but can anyone confirm a good replacement for me? would the one posted earlier from aliexpress work? thanks

[wraper]

This is the model number of the display. I really don't know anything about them but can anyone confirm a good replacement for me? would the one posted earlier from aliexpress work? thanks

You need to check dimensions and exact pinout, and compare with aliexpress listings or datasheets. Easy to do by touching terminals with unearthed soldering iron, some phone charger or anything else that has some capacitive leakage from the mains voltage. I'm pretty sure such displays are still sold by western distributors like Mouser too. Suggest replacing both displays, for matching appearance and long term reliability.

[wraper]

From mouser https://www2.mouser.com/ProductDetail/Lumex/LCD-S3X1C50TR-A?qs=co%252BsI3njzXnY%2FLRcWVtG9g%3D%3D

[Swake]

3 1/2 digit LCD. Typically driven by an Intersil ICL7106 A/D chip. If that is the chip you have it is a very common display.

Edit: didn't notice the pic of the board, yes that is the chip you have. the second chip is likely a clone or already a repair.

[wraper]

Edit: didn't notice the pic of the board, yes that is the chip you have. the second chip is likely a clone or already a repair.

They are both clones. NTE2051 from NTE and TC7106 from TelCom semiconductor (acquired by Microchip). Both look quite old.

[Brad808]

Thanks folks. I ordered this https://www.aliexpress.com/item/33060132278.html?spm=a2g0o.productlist.0.0.3674231au3EjPy&algo_pvid=c0851635-7431-4af7-a0aa-260edbde8603&algo_exp_id=c0851635-7431-4af7-a0aa-260edbde8603-7&pdp_ext_f=%7B%22sku_id%22%3A%2267620932126%22%7D&pdp_npi=2%40dis%21CAD%214.18%213.71%21%21%21%21%21%402101d68d16693274316274449e0aeb%2167620932126%21sea&curPageLogUid=NMpKzJ7Gvjnu

I checked the pinout and dimensions vs the bad one and it seems to line up perfectly. Fingers crossed.