Unknown HP module, who has an idea what this is  - Page 1
Forum section: electronics / projects

author: prutser
author_rank: Regular Contributor
timestamp: November 24, 2023, 01:17:29 pm
content: I bought a couple of HP parts as a kind of "surprise package" no idea what it was, expected something like an oscillator. Until now I have no been able tofind a datasheet. Based on the trimmers and the pin at the bottom right it seems indeed something like an oscillator.Someone an idea what it is ?It has 7 pins from which 3 are GND. The pin at the right bottom looks an output.Both + connections of the tantalum caps are not connected to each other (if so it is most likely Vcc) It might be that both are Vcc but different voltages.

author: wofritz
author_rank: Contributor
timestamp: November 24, 2023, 01:39:19 pm
content: Internet search for m1400-61544 returned this:https://www.scribd.com/document/665857585/Philips-50T-Fetal-Telemetry-System-Service-manualI downloaded the PDF in spite of the safety warning and it seems that module could be a VCXO. With this type that instrument has a "channel frequency" of 433.25 MHz, which of course does not mean that the VCXO (if it really is a VCXO) runs with this frequency.I would try to find out what the VCC and GND pins are, which should not be too difficult, and then connect it to a DC supply with current limit and starting with about 5V and slowly increase it until there is a signal at the output.Maybe the service manual in the link above gives more information.

author: prutser
author_rank: Regular Contributor
timestamp: November 24, 2023, 03:48:55 pm
content: Thanks, I probably ignored the Philips related search results. More or less expected some HP datasheet or equipment. But indeed it is used in this Philips equipment.I have several of them with various different partnumber extensions. The service manual has some tables listing the parts all with different frequencies.The S/M does not contain schematics, but from a block diagram I know which voltages are available. (cannot determine which ones are used for this module, but probably not difficult to find out)It is stated as a VCXO. Initially I expected the big metal can to be a transistor, but must likely it is a crystal. It has 3 pins, the case is connected to the center pin, which with this type of transistor is usually the base (and is connected to GND here).It seems to require 2 voltages ( -3.5V and +5 or +8.5V ) connected both but didn't happen much (only a few 100uA drawn at the negative voltage). Probably some control pin is required to switch it on. I will spent more time on it if I ever need a VCXO in this freq. range

author: wofritz
author_rank: Contributor
timestamp: November 24, 2023, 03:59:23 pm
content: I won't expect it needs other voltages than the +5V. From the service manual I think the negative voltage and the 8.5V are for other circuits in that Philips thing. For a VCXO I would expect GND, VCC (+5V), output, a control voltage for frequency control and maybe a digital input to enable the output. It should not be too difficult to reverse engineer it to find these signals on the pins.

author: prutser
author_rank: Regular Contributor
timestamp: November 25, 2023, 10:46:59 am
content: There are 2 tantalum caps on the PCB. From one the positive is connected to GND, from the other one the negative is connected to GND.From the one with the positive connected to GND, the negative goes via a relatively low value resistor to one of the module pins, so I assume that's requiring a negative voltage.(can also be it is generating a negative voltage, but then I wouldn't expect the series resistor)The other tantalum is also connector to a resistor (10 ohm) but the other end of the resistor doe not go to a module pin. I expect somewhere a transistor as switch or regulator in between.