Damaged BK 885 LCR schematics anyone? - Page 1
Forum section: electronics / repair

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2017, 12:35:13 am
content: I have a damaged BK Precision LCR, model 885 that no longer works. BK scrubbed the PN#s. Is anyone aware of schematics for it?There are three PCBs. The lower one appears all digital and contains the LCD and keypad. It seems to communicate with the middle board using serial. The middle board sends it's data back to the lower board using serial as well. The top board appears mostly analog. The resistance mode seems to work just fine. No other modes work. There appears to be no clock going to the test port. The diodes, resistors and inductors appear fine near the test port. If it was damaged looking at a live circuit, I don't see any visible signs of damage. The +/- supplies look good going to the top board.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 26, 2017, 10:51:51 am
content: a little more details and pictures if possible, i have searched the schematics, no luck, ask BK if they sell a service manual ??I never saw a leaked schematics ...Did you bought the defective one on Ebay loll there was one for a very low price ...you have 2 defectives model for sale on ebay israel

author: whitevamp
author_rank: Regular Contributor
timestamp: May 26, 2017, 02:27:17 pm
content: it took me a long time to come up with one for my B&K Dynascan 830

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2017, 04:40:37 pm
content: I gave up my eBay account I would guess close to 10 years ago.I did write BK asking for even something as simple as a BOM or stuff sheet. The meter was made by MOTECH PN# MT4080D. Not too long ago, MOTECH sold off the T&M assets to BK.https://www.pv-magazine.com/press-releases/motech-announces-sale-of-assets-of-test-and-measurement-departments_10005474/I believe the synthesizer is on the middle board and this is where the problem is. I spent a fair amount of time inspecting the board under the microscope. Solder quality looks really good. I suspect U202 may be the cause. This IC has several pins that route to the analog board but they do not appear to change states. This chip has several traces driving it that clock at a fairly good rate. I suspect this may be a DAC or some type of synthesizer. It is a 44 pin J lead device. A touch of cleaner, I can make out JAPAN. Possibly a B or 8 followed by 2 maybe a 354.I can see a few pulses from middle board to the analog board. I suspect these provide some sort of sample timing (sample and hold perhaps) and appear to run at the update rate. The remaining signals appear lifeless. They do appear to route the analog signals through this connector and the ADC does appear to work just fine.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 26, 2017, 09:02:39 pm
content: good clean picture would help

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2017, 10:43:12 pm
content: Quote from: coromonadalix on May 26, 2017, 09:02:39 pmJust doing a quick Google search, this person has all sorts of pictures of one on-line. Is there is something specific you would see?https://kknews.cc/digital/anmlvzx.html

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2017, 10:44:36 pm
content: Here are some others.http://bbs.38hot.net/thread-7832-1-1.html

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2017, 11:00:47 pm
content: What's left after they ground the crap out of U202. A total guess on my part that this is even the problem.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 26, 2017, 11:04:34 pm
content: oh they have done a lot to hide the parts number, lick your finger and apply it to the chip sometimes it helps to " show the part numbers "Remove the socketed chip carefully and check if the socket is good or cracked, we had this problem on our boards, check if the pins are oxidized, if the socket pins are good put the chip back gently ...

author: joeqsmith
author_rank: Super Contributor
timestamp: May 26, 2017, 11:28:59 pm
content: Quote from: coromonadalix on May 26, 2017, 11:04:34 pmThat IC was hit with some cleaner to get that shot, without it you won't see a thing.I had removed the IC when I checked the solder joints earlier. Again, this all appears fine. Do you have one of these? If so, can you check to see if the synthesizer is indeed on the middle board and what pin it routes to?

author: HwAoRrDk
author_rank: Super Contributor
timestamp: May 27, 2017, 01:15:14 am
content: Quote from: joeqsmith on May 26, 2017, 11:00:47 pmPretty sure that's the Oki logo to the left of 'JAPAN'. No idea on the part number though, sorry.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 27, 2017, 02:49:48 am
content: I dont have oneHere's my guess in the pictures, i've written with Ms Paint on the chipsMaybe the "OKI" is a 82c XX series cpu

author: joeqsmith
author_rank: Super Contributor
timestamp: May 27, 2017, 12:31:24 pm
content: It could be OKI but the spacing did not look right. Maybe.The 801 board with the LCD controller and such again does not appear to be the problem. This board is just the UI and communicates with the 802 board using a couple of serial ports. I suspect the synthesizer is on the 802 board.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 27, 2017, 01:06:28 pm
content: i think it look likeAnalog devices dds sythetiser series ad9854 ad9959wich i would find overkill for a 100-200khz lcr meters, but it would be very stable

author: joeqsmith
author_rank: Super Contributor
timestamp: May 27, 2017, 04:36:57 pm
content: I think we just have to wait and see if BK comes back with anything.I attempted to back drive the test port. Shown with a 0.47 and a 22uF. It looks like is really is just the synthesizer that it out.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 28, 2017, 04:44:05 am
content: what do you mean by back drive, the jumpers on the test socket ?The read values seems good to me ??0.47uf is 470 nf, at 1v test22uf seem ok too, at 50mv ?For my part i never test electrolytics caps past 100-120hz, if i can, i always test them outside circuits at 1 or 2 volts, low voltages aren't enough, i use mostly the esr mode, since i rebuild smps, in circuit testing sometimes is not good.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 28, 2017, 02:08:59 pm
content: Quote from: coromonadalix on May 28, 2017, 04:44:05 amI am using an external source to check out the rest of the meter.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 28, 2017, 05:26:35 pm
content: do you have a scope ?, putting a Ex: 0.1uf poly capacitor, set the highest output voltage test, and manually check every test frequency you have and probe if it's present ? on pcb test clips or between the 802 and 803 pcb ? you said it wasn't present, it was with the un opened lcr case ?

author: joeqsmith
author_rank: Super Contributor
timestamp: May 29, 2017, 04:56:22 am
content: Quote from: coromonadalix on May 28, 2017, 05:26:35 pmSure I own a scope. I went through all the combos of drive, frequency and mode looking at the test clips back to 802.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 29, 2017, 10:24:15 am
content: okay i hope you have some news from BK

author: joeqsmith
author_rank: Super Contributor
timestamp: June 01, 2017, 02:02:34 am
content: Thanks. They wrote back and provided some pretty good info. Time to setup a new account with Digi-Key and get some parts on order.You wanted to see the one I was working on.

author: coromonadalix
author_rank: Super Contributor
timestamp: June 01, 2017, 02:11:04 am
content: if its not too much to ask, what they answered you ??

author: joeqsmith
author_rank: Super Contributor
timestamp: June 01, 2017, 02:30:01 am
content: I have that section and even though they use a MOTEC PN, caused no problems. Rare I have seen a part fail but the synthesizer looks dead. Serial lines, clock, mode select, power supplies all look good. I wonder if anyone has done a study on IC MTBF vs grinding on the plastic.. Time to replace it.

author: coromonadalix
author_rank: Super Contributor
timestamp: June 01, 2017, 03:19:49 am
content: uh hard time to decode what you said ?? Motec is the sythetiser chip brand ??

author: joeqsmith
author_rank: Super Contributor
timestamp: June 01, 2017, 12:01:46 pm
content: Motech was the OEM for the meter and rebranded under BK. They provided the schematic but Motech uses their own PNs instead of the OEMs. Looking at the signals to the synthesizer, everything looks fine. It seems the synthesizer IC itself is bad. It is rare I see damaged ICs with a good design and wonder if grinding on the plastic packages changes their sealing properties. Mean Time Between Failures, or failure rate may be effected and I wonder if someone had done a study on this.Parts are on order. Maybe next week I will try it out, only to find something else is wrong.

author: coromonadalix
author_rank: Super Contributor
timestamp: June 02, 2017, 12:25:28 am
content: ahh ok Motech MT4080 and MT4080A models ...

author: joeqsmith
author_rank: Super Contributor
timestamp: June 06, 2017, 01:23:33 am
content: Looks like it was the synthesizer. If it comes up again, the part is U212 AD9832BRUZ 10BIT 25MHz DDS.Cap with and without series 10 ohm. Need to do a full checkout next.

author: coromonadalix
author_rank: Super Contributor
timestamp: June 06, 2017, 01:38:12 am
content: nice to see your repairs, did they sent you part numbers or schematics ??

author: joeqsmith
author_rank: Super Contributor
timestamp: June 06, 2017, 02:50:35 am
content: Sorry but I am not willing to disclose any information beyond what I have shown without approval from BK.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 07, 2017, 12:24:35 am
content: I did ask BK for approval to release all the documentation they provided but they do not want it disclosed. However, they said they will release information on a case by case basis to customers. I think I just got lucky. So BIG thanks to BK for letting me save this one from the recycle bin.