I have this device in my drawer:
Some images of the outside are here:
The problem is I cannot find a manual or anything on google that says what this is.
Worst of all, it does not even tell me how much voltage it wants or if it is center positive or negative.
Is it possible to figure this out from the circuit board somehow? It seems 5V, but I don't want to risk it and burn something out.
TL;DR most likely it is either a 9V or 12V input, centre-positive
Following the power trace from the DC barrel jack:
We see it appears to be a centre-positive jack (the shell appears to head into the ground plane). The centre-pin runs on a trace which heads up to the centre of the board, where we find this little sub-circuit:
Reading the ident on that chip we get ?4063, which is undoubtedly an MC34063A DC-DC converter.
The following is a typical application circuit from the IC datasheet for the MC34063A in a step-down configuration.
Tracing out the components on your board, while difficult to tell from the one angle, it appears to follow this circuit pretty well, with what appear to be the same component values, almost. The current limit resistor appears to be 0.15R (possibly 0.015R, its a weird code). The inductor appears to match too at 220uH. I can read 122 on the resistor from pin 5 to GND, so 1.2kR, and there is a second resistor which could read 3801 which would be 3.8kR which match the divider values for 5V output.
Based on that, the input must be higher than 5V in order for the MC34063 to function as a buck converter. Based on the example design in the datasheet, the inductor size would be functional for an input of 8V to 16V. So most likely it is either a 9V or 12V input.
(1)
You can find the GND (center POS/NEG) by probing with a multimeter. Probe around the capacitors on the PCB, as they all have a negative pin on the GND side and most likely no direct connection to the POS input.
You could also identify a component pin directly soldered to the GND-fill on the PCB visually.
(2)
By connecting a variable voltage-source to the POS pin and ramping it slowely from 1V8/3V3/5V0 until the circuit starts operating. I would personally guess either 3V3 or 5VO, as i cant see a pre-reg.
(3)
You could also write a email to the company or call them.
If you don't speak italian: Don't worry - englisch is fine most times.
If you didn't buy the component first-hand: Don't worry - most likely they will help.
Edit As i could not find a Codice-Fiscale: The company is most likely "gonski".
(4)
According to this spec-sheet - which uses the same ISDN interface APC5568-5V - i would say with some confidence: The circuit operates from 5V DC.
According to this memory datasheet i would strongly suggest, that the circuit operates from 5V0, as i can't see a DC/DC or pre-reg on the board.
(5)
Please see @TomCarpenter's answer - just excellent.
This is what I would do:
First check any diodes or glean anything from the pcb. The easiest thing to do would be to probe VCC on the crystal lan CS8900A where does its VCC go to? There is probably a regulator on the board somewhere, look up it's datasheet
I think it's likely an ISDN voip gateway, you have 3xrj11 ports for telephony, one rj45 for data and maybe the other rj45 is for serial access.
The internet archive has their site saying they specialise in:
• POS teminals and EFT Server. • Remote Terminals (Remote Banking). • Protocol conversion for data transmit.
https://web.archive.org/web/20031225141510/http://www.incaa.it/english/weare.html
Here's a product I think might be similar: https://www.ebay.com/itm/275664478417
This might have been used to connect various Point-of-sale devices (card reader, etc.) to a network.
I agree with others: First I'd contact the company for an absolute answer instead of guessing; there's an email address on that label! They WANT to help you, they WANT you to like/use their product, if not sell you an AC adapter.
Secondly, it looks like the center pin is positive. You can confirm that with an ohmmeter as the long, silver, solder strip/path on the edge of the board is most likely (99%) negative.
I like @Tom Carpenter's IC identification. But if all else fails, you can start by applying 5 volts (as with a variable power supply) and looking for signs of life. If not, then 5.5... Then 6.0... Then 6.5...
Determine the higher of the two voltage values on those blue capacitors; write it down. Then note the maximum value of the IC's input; write it down. I wouldn't go beyond the lowest of those written values.
