La Crosse BC-700 battery charger (issue with buttons)

[13hm13]

The La Crosse brand is one of many brands (eg. Technoline, etc)  that have re-packaged this very popular AA/AAA batt. charger. (Probably made by common Chinese manuf).

Anyway, this BC is know for its flaky push buttons that go bad. Here's a video of someone repairing one:
https://youtu.be/Husb1Aaa5HA

I have no idea about the full history of my unit except that it came from a house that was roach-invested. Prior to opening, the unit was apparently charging fine (??) but some of the LCD display was not showing upper half. (Later isolated to a dirty Zebra strip -- easy fix).
Upon opening the unit, there was a literal ecosystem of small roaches and spiders (all alive and scurrying). And many dead bodies of roaches (or were they molts??). I'm assuming they chose the interior for its warmth. I have seen roached infest modems, routers, etc.
Anyway, after air blasting the mess -- very dense -- and following it up with a 95% iso alch + gentle toothbrush and q-tip wiping (and it is v. difficult to remove the roach excrement) ... and following it up with MULTIPLE q-tip/alch and Deoxit treatments of the contacts, I still can't get bank selector switches 2,3,4 and the MODE button to work. It is possible, that the brand new unit was also defective--out of the box (). The condition of the non-working buttons/switches (the PCB contacts, and the depressible aluminium momentary switch itself, are in the same condition as the working switches, if not better).
I did check all the elctro caps on the PCB and in the wall-wart ... all test fine.
The unit works / displays fine ... incl. most of the other buttons/functions.

The non-working switches are a mystery?

[abdulbadii]

as usual
picture, please ?

[13hm13]

as usual
picture, please ?

It would help if you actually read the first post carefully and watched the linked YT video.
Anyway ... some photos I snapped ... note that only the top of the board has the roach excrement stains --- much has since been removed; it does not seem to be corrosive. The bottom (component side) was completely ignored by the roaches.
It's possible that a roach short damaged a transistor, or passive, creating the non-functioning button.

[SilverSolder]

I have a similar unit, owned from new.  Even when working at its best and brand new, the buttons are "hard of hearing" and often need multiple hard stabs (even after Deoxit etc. treatment). 

Is yours "hard of hearing" or is it stone deaf?

[commongrounder]

Well that’s pretty darn gross! 
Can you tell if the deposits ate through the conformal coating? I see several places where a stain bridges circuit traces, which could short control signal lines.
I also have a (clean) copy of this charger, which is “hard of hearing” in the button department as well.

[13hm13]

Hey folks .... y'all keep askin' the same stuff I covered in prev. posts in the thread. Y'all make the roaches look like geniuses -- at least they are smart enough to survive
SIGH!!! .... no, as noted prev., the roach poop did not eat thru the conf. coating  ... it comes off with 99% alch and q-tip. Though a little elbow grease is sometimes necessary.
About the buttons ... Banks 2, 3, 4 and MODE are completely unresponsive. Ever after multiple acetone/alch and Deoxit rounds. All other buttons and functions work and act normally.
About this unit:
Prev owner had it for about 10 years, used it for about 1hr once a month, then unplugged until next month. So relatively low hours. Also, owner (elderly gentleman) NEVER used any of the buttons (advanced features) ... it was simply the same ritual:  plug in cells, wait for BC to display 'FULL' and then unplug till next month.
Given the sheer number of complaints about this unit's buttons -- search Google -- I'm going to say it may be "open" or defective components or poor solder joints, etc.

[SilverSolder]

The deafness can be down to either bad switches, or a bad circuit supplying and/or reading the switches.  The switches are either being scanned by the micro, or there may be few enough switches that a dedicated I/O line for each was possible.  So there would either be a constant sensing voltage on the switches, or a pulsating one (if scanned).

Is it possible to run the unit outside the case, and put a scope or a DMM on the button pads to see if there are any signs of life?  Alternatively or additionally, try short circuiting one of the switches manually with a jumper wire, and see if you can trigger the button functionality that way? 

[13hm13]

The non-working buttons DMM (cont. test) work just fine on the PCB test points -- i.e., same as working buttons.

I did begin some component-by-component testing on the PCB ... and found a possible problem for the MODE button circuit. Note the "154" smd R. It should be 150k, but my Fluke 87 reads 6.7M. Haven't gotten round to replacing it. It may have blown because of a faulty transistor, etc. Dunno!

[SeanB]

Looks like it is made using recycled parts, so the resistor failing is just that, the resistor failed, probably because the recycling was done using a scraper over an open fire to melt the solder off.

Switches being grumpy is just old switches, they are cheap, so get new ones, preferably actual brand name ones instead of the mystery recycled ones it used.

[SilverSolder]

The non-working buttons DMM (cont. test) work just fine on the PCB test points -- i.e., same as working buttons.

I did begin some component-by-component testing on the PCB ... and found a possible problem for the MODE button circuit. Note the "154" smd R. It should be 150k, but my Fluke 87 reads 6.7M. Haven't gotten round to replacing it. It may have blown because of a faulty transistor, etc. Dunno!

Could also be that the solder joint has cracked, might cure the problem to just touch up the solder!

[13hm13]

UPDATE:
Removed the "154"R. Very messy .... one trace pad lifted off (!!) so had to trace that pad to trans. pin. SIGH!! Upon removal of the "154"R (which, again, my Fluke 87 read as 6.6M), the BC was plugged in ... NO display at all (unit was dead). Bodged in a 100K R (all I had). Unit working again ... but NO CHANGE in functioning/ non- functioning buttons. In other words ... all that work for nothin'!

[SilverSolder]

UPDATE:
Removed the "154"R. Very messy .... one trace pad lifted off (!!) so had to trace that pad to trans. pin. SIGH!! Upon removal of the "154"R (which, again, my Fluke 87 read as 6.6M), the BC was plugged in ... NO display at all (unit was dead). Bodged in a 100K R (all I had). Unit working again ... but NO CHANGE in functioning/ non- functioning buttons. In other words ... all that work for nothin'!

You have already checked continuity at the buttons.

But do you have a way of checking if there is a sense voltage present at the buttons?  E.g. a voltmeter and/or a scope across the contacts....  is there anyone home?

[13hm13]

It's possible that firmware got corrupted. Mr Carlson's recent repair video featured a coffee maker that was repeatedly plugged/unplugged. Carlson speculated that that's why the pump motors were not operating at full speed (and full duration).

About that "154" R ... well I measured it MANY times prior to removal (6.6M). I also measured many R's on the same PCB, just to make sure my DMM was working normally. It was.
Maybe the "154" was mis-labelled from the SMD resistor factory? Maybe it was dis-labelled (to prevent reverse engineering)? Maybe its value had changed, with age, but allowed just enough juice the flow thru to make the damn thing work?
In any case, the 100k bodge got the BC back to its original cond.