Testing a crystal oscillator with an oscilloscope  - Page 1
Forum section: electronics / beginners

author: pman92
author_rank: Contributor
timestamp: April 24, 2023, 09:58:25 am
content: Hey guys,I'm attempting to repair the speedo in an automotive dash cluster from a 1995 Nissan Navara.The cluster is manufactured by Kansei and is fairly simple. It receives an AC voltage signal input from a 2 wire inductive speed sensor. It has a proprietary silicon DIP36 main IC / microcontroller which processes the signal and drives an air core gauge needle to display vehicle speed, a stepper motor to advance an otherwise mechanical odometer counter, and generates a "2-pulse" output which is sent to the engine computer in the vehicle.Currently none of the above work. I have dismantled the speedo and applied power and ground on the bench. The proprietary IC seems to be powered with a regulated 8v. I have applied an AC voltage input signal using a signal generator and confirmed it is making it all the way to the IC (it enters via some basic circuitry that uses a zener diode to limit the amplitude to approx 1v). I have reflowed all the solder joints which made no difference. Capacitors all look visually ok and none are shorted.I assume it is probably a faulty microcontroller, but there is 1 other component which I would like to test. It has an external crystal oscillator (see image).I attempted to see if it was working using my oscilloscope and a 20x attenuator. Neither of the 2 pins showed anything happening.Is there a way to test to see if it is faulty?Does 501 mean anything in the way of what frequency it should be?Thanks in advance

author: Vovk_Z
author_rank: Super Contributor
timestamp: April 24, 2023, 11:08:31 am
content: I'm not sure it is a crystal oscillator, although: There is a similar part marked as 'XTAL'...1998 Nissan Navara gauge cluster repair (video).

author: MathWizard
author_rank: Super Contributor
timestamp: April 25, 2023, 12:25:59 am
content: Yeah out of circuit, does it measure 5.1nF ? Personally I've never seen a crystal or xtal that was not in a metal can.

author: pman92
author_rank: Contributor
timestamp: April 25, 2023, 02:00:05 am
content: It is labelled XTAL on the PCB (the same as the later model cluster in the youtube video above), hence I assumed it's a crystal. But maybe it's a capacitor that controls the internal clock of the microcontroller somehow?However it does have 3 connections. It's a SIP3 package. The outer 2 pins running to the microcontroller and center pin straight to ground. If it was only a capacitor it wouldn't have 3 pins

author: james_s
author_rank: Super Contributor
timestamp: April 25, 2023, 03:53:04 am
content: That's a ceramic resonator with internal loading capacitors, these are very common in low cost devices like TV remotes. The center pin is the ground pin that the capacitors connect to and the other two pins are connected to the resonator. The problem could be either the resonator or the IC, if you want to test it you can do so with a basic crystal oscillator circuit. Otherwise you can try replacing it, a quartz crystal or resonator of the correct frequency ought to both work equally well, you'll need a pair of loading capacitors to use a bare crystal, 18pf is a common value.

author: geggi1
author_rank: Frequent Contributor
timestamp: April 25, 2023, 04:22:38 am
content: JUst build a test oscillator like this one.http://www.circuit-diagrams.net/page/two-simple-crystal-test-circuitsBy using a High-z probe you can measure if it is oscillating in front of the OA91 diode.The OA91 can probably be replaced with something more common like a 1N4148

author: wasedadoc
author_rank: Super Contributor
timestamp: April 25, 2023, 07:57:53 am
content: Quote from: geggi1 on April 25, 2023, 04:22:38 amThe OP has a 'scope and can probe the transistor collector. Does not need any of the components to the right of that point.

author: geggi1
author_rank: Frequent Contributor
timestamp: April 26, 2023, 09:03:46 pm
content: Quote from: wasedadoc on April 25, 2023, 07:57:53 amMy idea is to remove the exsisting circuit from the equation.If the resonator is ok in the test circuit then start to look into the speedo.It is also a handy circuit for testig other chrystals.

author: james_s
author_rank: Super Contributor
timestamp: April 26, 2023, 11:45:21 pm
content: Quote from: geggi1 on April 26, 2023, 09:03:46 pmYes but he still only needs part of that test circuit, he has a scope so the meter and associated bits are not needed, just a basic oscillator.