What secret lies under that blob?

[MrAureliusR]

The word 'secret' is being used differently than usual here. Another weird English thing. He doesn't mean secret as in restricted, kept hidden, etc. but more as in wanting to discover something new -- 'the mysteries within'. Yeah you can look at images etc. but decapping it yourself is always more fun, plus it's cool to actually see the bondwires etc. Until you see them in real life it's hard to appreciate just how amazing ICs really are.

Yes, you could discover the same things by decapping any IC. But I've always wondered what's under the blobs -- it must be interesting to see the bare die with bondwires going directly to pads, instead of inside the plastic packaging that's usually surrounding it.

If you don't understand why someone would want to do this...  there's not really any explaining it.

Thanks for typing that up and well worded unlike what I would respond as , as I really dislike those anti hands on bookish Anal NerdBurglars that have "opinions" who still wouldn't get it no matter what imo , cheers ...

I'd say that's taking it a little far... free_electron in particular is just being practical about it. He's taught many, many beginners to electronics and so just suggests you spend your time learning more useful things. I agree; I'm just saying as a side note it can be entertaining and slightly informative to open up the blobs.

[EvilGeniusSkis]

I have one of the mastercraft DMMs in question I'll take it apart AND turn it on (take that Dave) and see what I can find.

[EvilGeniusSkis]

Just finished investigating, most of the traces look like they are for driving LCD segs. Some are obviously for measurement input but no unused serial connections. 

[SeanB]

Youwill find 2 unconnected pads at the left side of the pattern of pads that are the serial port connections. As the traces are not going under the blob there is no way to get IR data out of it short of decapping the blob which is likely to be terminal. otherwise you need to pop it off and put the right Cyrustek DMM chip in there instead. At that price it would be better to buy one with the IR onboard though.

[Monkeh]

Where is the assumption that it's a Cyrustek or Fortune IC and that it has serial coming from?

[SeanB]

I have seen ( and bought) the cheapies that have a bigger brother with the same features and identical specs but with serial output.  Looking inside you see the same COB but with the 2 pins connected and fitting the Cyrustek pinout for the DVM chip in question. The cheapie has a close to identical COB but those pins are not brought out via bonds to the pads.

[MatCat]

I am curious, you can't find bare die on Digikey, so I assume the companies that do mass production get them directly from the manufacturer?  Has anyone here actually done any design work using a bare die, if so what is considered the magical production number to make it financially viable?  (Obviously you need to be able to bond the wiring, which I am sure is some amazingly expensive equipment).

[Monkeh]

I have seen ( and bought) the cheapies that have a bigger brother with the same features and identical specs but with serial output.  Looking inside you see the same COB but with the 2 pins connected and fitting the Cyrustek pinout for the DVM chip in question. The cheapie has a close to identical COB but those pins are not brought out via bonds to the pads.

And if you look at this one you'll see all the pads bonded, all of them used, and nowhere for an IR LED to be connected. You'll also note that at 40 pins, it matches the pincount of a 7106/7136, and the various Fortune or Cyrustek chips are all 64-pin or bigger (except the.. 7106/7136 clones!).

[tom55]

If you tried to remove the blob you would find a bare die without markings.

removed one from dt830b and it's true. this doesn't help me at all.

i have dt9208a that needs new chip, this revision XT9208B, GND pin is the most right in a bottom row. ICL, intersil, AME etc. pinouts do not match

anyone knows what to put here?

[magic]

These chips support extra features like low battery indication or HOLD which IIRC were not present in "Western" 7106 type chips.

Based on this, I concluded that they are likely specialized Chinese chips from unknown vendors, not widely available and with no datasheet unless you are UNI-T ordering a million of them.

edit
Many new DMMs use other chips with delta-sigma ADCs, autoraning and stuff. But the DMM above is probably traditional 7106-style because it contains a film capacitor, footprint for a trimming pot (newer chips would have a calibration EEPROM instead) and seems to be manual ranging.

edit edit
This looks like QFP44 footprint, doesn't it? I went to AliExpress and found a few offers of ICL7106 in this package. Maybe worth giving a try just to see what happens.
Or fork out $10 for a new DMM.

[tom55]

actually i looked up aliexpress and ebay, found the identical one as i have, ordered at aliexpress - listing said last item in stock, a month later empty bag comes...
just two days ago i got dmm ordered on ebay, and of course it is not the same one although looks almost identical

the idea was to first test both energizer batteries in new unit (as i've previously seen some batteries are just not good for this device) and then compare measurements on PCBs

the thing i received works on AAA batteries, PCB is different without external IC components, in general i don't like it: screen tries to follow up with fancy models by adding unnecessary AC,DC,ohm, buzzer etc symbols ending up in reducing actual digit thickness, but worse than that is viewing angle is practically useless
it also auto shuts down every 10 minutes, even if it is in use during that time. and makes a lot of annoying beeping, before auto shutdown and while changing range. when i only want it to beep in continuity mode. plastic casing looks of worse quality than earlier revision as well as sticker on top of it with all the range indicators (i did not even realize this is a sticker, because it looked way more realistic on earlier revision, until i noticed this on new unit). the item is the same as on attached photo, just without any logo on top, only DT9208A printed (PCB is XT9208V2)

definitely need to repair my old unit, no way i can use this and be happy with it

[coromonadalix]

i too was always curious about theses blobs  but as written  you may need some acid  ...  etc  ... to get to it,  i tried acetone   it wont dissolve loll

it like ceramic epoxy really hard ...

see picture from the web

[tom55]

yeah, you need way more dangerous stuff than acetone. i took mine off with scalpel and hot air. was useless anyway as the dt830b was damaged too

[magic]

Flame turns the epoxy into something akin to charcoal which is easily removed afterwards, if you don't mind ruining the PCB.