Salvaging components from an intermittent PBC. Never/Maybe/Always?

[paul8f]

Trying to diagnose a problem on a new board lately. On average, in ten iterations of the test script it will fail just once. Difficult to pinpoint the fault. Temperature cycling, voltage margining and board vibration/flexing reveal nothing. Power rails look clean, and oscillators are stable. Problem is hardware, not software/firmware. Don't think there are any pressure-sensitive ICs or leaky caps etc.

Because it's intermittent, this should go straight onto the scrap heap. On the other hand, if it was actually a hard fail but BER, then it could be used as a doner unit for repairing other devices with certain components salvaged.

So, just wondering is there any rule of thumb for saving components from a scrapped intermittent board?  - Never ever, only re-use passives, re-use basic discrete silicon components but only after thorough component-level tests?

Interested to hear what people think, or experience you've had. What's the probability of transferring the original intermittent fault to another board?   

[ogden]

Interested to hear what people think, or experience you've had. What's the probability of transferring the original intermittent fault to another board?   

It depends on so many variables that it is impossible question, especially when cost of the board/product are *not* provided. Usually you just repair board - obviously when it is economically feasible. If you can't fix it - scrap it. Rarely you take off some expensive component when you know it is 100% operational and can be reused for repairs of other boards. For example LCD or power supply module.

[PKTKS]

Hard to guess without the details  ..

you said :  SCRIPT . I will assume a motherboard.

Likely you have memory chips.  TOP of the list. faulty memory

or wrong memory specs kinda...

I have a BOX FULL of crappy DDR modules...

Which I would like to test... but I refuse to mount whole
MOBOs for the sake of probing crappy DDR modules..

I wonder if someone somewhere already developed a DDR
tester...  cheap and easy like  EPROM testers..

but DDRs are more tricky and way fast than EPROMs

Paul

[paul8f]

Hard to guess without the details  ..
... you said :  SCRIPT . I will assume a motherboard.

Just a few more details here.... No, it's not a motherboard. It's a small board worth around €100-€120, mainly housing DACs, a peltier device control unit, and a precision current monitor. Relatively cheap board, but it's only a sub-assembly to a larger unit worth many times it's own value.

Lots of op-amps, a multiplexer, bi-polar transistors and the usual mix of diodes, resistors, inductors and capacitors. Hard to decide what's safe to salvage (if anything...)

[paul8f]

I recommend to nuke this board in the reflow oven for a second pass, and see what happens.

Made by an external CM. Good suggestion though!