[FOUND] Looking for service manual/schematic for BK Precision 891 LCR meter - Page 1
Forum section: electronics / testgear

author: n1ist
author_rank: Contributor
timestamp: May 07, 2025, 04:57:29 pm
content: A BK Precision 891 LCR meter followed me home from the last MIT flea, and it has some issues. It powers up fine and passes POST but when I try to do an open or short calibration, I get a cal failure. All power rails look OK, and during the open cal, I see a varying frequency sine wave on Hcur and two sweeps (one varying frequency, and then one varying amplitude) on Hpot.*IDN? returns B&K Precision ,891,468C23350, 3.03/ 1.68 / 4.01BAnyone know where to find a schematic or service manual for this meter, or have any ideas where to look for the issue? Thanks./mike

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: May 07, 2025, 05:58:31 pm
content: Hello Mike N1IST,I would give it a shot and ask BK Precision if they could help you with a schematic or some advice.Can you take a few pictures of its' guts and list the main ICs ?

author: n1ist
author_rank: Contributor
timestamp: May 07, 2025, 06:46:28 pm
content: The front end is all simple (mainly opamps and analog switches) going back to a TMS320 DSP. Nothing looks damaged and I checked all of the diodes at the front end (all are good) just in case someone tried to test a charged capacitor. I will try contacting BK.

author: KungFuJosh
author_rank: Super Contributor
timestamp: May 07, 2025, 06:57:43 pm
content: C322 looks suspicious.

author: Martin72
author_rank: Super Contributor
timestamp: May 07, 2025, 08:22:37 pm
content: Yes, please upload a clearer picture of that.

author: n1ist
author_rank: Contributor
timestamp: May 07, 2025, 11:11:58 pm
content: Good catch; I will look at it tomorrow. Thanks to timeandfrequency for making the obvious suggestion; BK sent me the schematic and service manual (unfortunately, they did ask me not to share it) so hopefully it should be rather easy to trace thru the signals./mike

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: May 08, 2025, 02:27:14 pm
content: Quote from: n1ist on May 07, 2025, 11:11:58 pmTrue fluke. This will significantly ease your work.I can also understand that BK asked you to not disclose SM and schematic.However, once successful repaired, it would be nice to indicate the ICs and other parts (silkscreen ID, part reference) you replaced to solve the issue.Analog swiches are rather failure prone and also experience partial malfunction.To go straight, I would suggest you to actually buy from Mouserkey^^ all of the ICs used in the front end.For 20-30 bucks, you should be back in business.

author: scott batchelder
author_rank: Newbie
timestamp: August 28, 2025, 07:24:34 pm
content: I have a black screen on my bkprecision 891. All LEDs light up inside. I read on the blog of voltage regulator failures. Please advise?

author: MathWizard
author_rank: Super Contributor
timestamp: August 30, 2025, 04:21:39 am
content: For your black screen issue, what voltages are around the LCD ? I'd check the easy things 1st like loose connectors. Is there any type of a reset you can do? Maybe hold down certain buttons on power on??You should probably make your own thread in the main Repair section, you will get more views and help.Does it sound like the meter is still working ? Do pressing buttons do anything like makes beeps or change range relays or anything ??If it was a regular LCD TV/monitor, if all the voltage rails were working, I'd be looking for the high power section for the LCD backlight. I'm guessing in these little things, the LCD is one unit, connected w/ pwr and data lines. And it won't need a big power section like a TV. So I'd see what voltages enter the thing, and see if there's digital data getting sent to it still.At least on TV/PC parts, a lot of these chips and modules, will have a reset or shutdown pin, that will disable the device if there's a problem, or to save power, etc.