Damaged BK 885 LCR schematics anyone?

[joeqsmith]

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. 

[coromonadalix]

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

[whitevamp]

it took me a long time to come up with one for my B&K Dynascan 830

[joeqsmith]

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.   

[coromonadalix]

good clean picture would help

[joeqsmith]

good clean picture would help

Just 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

[joeqsmith]

Here are some others.

http://bbs.38hot.net/thread-7832-1-1.html

[joeqsmith]

What's left after they ground the crap out of U202.  A total guess on my part that this is even the problem. 

[coromonadalix]

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 ...

[joeqsmith]

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 ...

That 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?

[HwAoRrDk]

What's left after they ground the crap out of U202.  A total guess on my part that this is even the problem.

Pretty sure that's the Oki logo to the left of 'JAPAN'. No idea on the part number though, sorry.

[coromonadalix]

I dont have one

Here's my guess in the pictures, i've written with Ms Paint  on the chips

Maybe the "OKI"  is a 82c XX series cpu

[joeqsmith]

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.   

[coromonadalix]

i think it look like 
Analog devices dds sythetiser series ad9854 ad9959   wich i would find overkill for a 100-200khz  lcr meters, but it would be very stable

[joeqsmith]

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.     

[coromonadalix]

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 test
22uf  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.

[joeqsmith]

what do you mean by back drive,  the jumpers on the test socket ?

I am using an external source to check out the rest of the meter. 

[coromonadalix]

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 ?

[joeqsmith]

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 ?

Sure I own a scope.  I went through all the combos of drive, frequency and mode looking at the test clips back to 802. 

[coromonadalix]

okay   i hope you have some news from BK

[joeqsmith]

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. 

[coromonadalix]

if its not too much to ask,  what they answered you ??

[joeqsmith]

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.   

[coromonadalix]

uh  hard time to decode what you said ??  Motec is the sythetiser chip brand ??

[joeqsmith]

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.