how do I check if an IC is working.? - Page 1
Forum section: electronics / beginners

author: jorgeh
author_rank: Regular Contributor
timestamp: July 11, 2022, 07:06:24 am
content: Hi All.I get on a regular basis old boards, and after checking the prices of some ICs I was thinking to start selling them on ebay.If I want to say that it was checked and in working conditions. is it enough to check voltages?I dont have access to an osciloscope.Most of them I think are deprecated. replaced by other. but maybe for hobbyst/students could be usefull.

author: jorgeh
author_rank: Regular Contributor
timestamp: July 11, 2022, 07:07:30 am
content: any ideas on how to check the big ones?

author: Berni
author_rank: Super Contributor
timestamp: July 11, 2022, 08:02:21 am
content: It is impossible to know without having a test circuit that actually runs the chip. Not only does the chip have to function but it also has to meet performance specs. (Like a very slightly damaged opamp might work but have excessive input offset)But you can check for signs of a chip being blown. A lot of the time when a chip blows it blows completely dead. This usually shorts the supply rails and makes the chip get really hot. Sometimes a sign of this can be seen as discoloration or even distortion of the chip package in the middle where the die is located. Sometimes it is not visual and only gets hot, or sometimes the bond wire blows like a fuse cutting the chip off from the supply. So if you check the datasheet for what supply voltage it needs, give it that supply voltage and check that the supply current being drawn is within what the datasheet says it is supposed to be. Another way is fo use a multimeter on diiode test to check if you see ESD diodes on pins rather than opens or shorts.

author: Gyro
author_rank: Super Contributor
timestamp: July 11, 2022, 08:06:28 am
content: There is really no way for you to be able to test the ICs in isolation. There are many analogue and analogue-digital parts which you won't be able to tell are working within specification. You are more likely to damage them during removal and test attempts than if you leave them in position.My suggestion would be to offer the whole PCBs, either on the forum buy/sell/wanted section or on ebay. I'm sure the people who frequent the Metrology section would be prepared to offer you a reasonable price.It would be a shame to damage some reasonably rare components by attempting to remove them.

author: AndyBeez
author_rank: Frequent Contributor
timestamp: July 11, 2022, 08:49:55 am
content: You are right to consider the chips on your boards as valuable but do not touch any of the components. You do not have to.There are companies and private individuals who specialise in stocking hard to find reclaimed semiconductors. They have the ESD compliant means for safe removal and, the test equipment to guarantee an IC is to spec. Those guys sell to retro home micro and games machine restorers. They can hold their stock for decades!List your boards for parts not working, and use keywords such as rare, retro, recycle and repurpose. Or as @Gyro suggests, offer them in the Buy/Sell section as parts magpies lurk here too.

author: jorgeh
author_rank: Regular Contributor
timestamp: July 11, 2022, 05:23:28 pm
content: Hi thanks for the tips they are really usefull.Then im gonna make better pictures of the boards.For price research I use sold items on eBay, Mouser and Rochester Electronics. but since most of them are deprecated I sometimes only find them on eBay. are there any other websites I can research the price?How could I determine a fair price.?For specialized companies I know here in germany Demontronic.Tnx again for the replies.

author: Gyro
author_rank: Super Contributor
timestamp: July 11, 2022, 06:56:13 pm
content: Some parts are straightforward, but those are also the more comodity ones, used prices are (should be) nowhere new price.The more specialist items are more collectors' items these days (the AD hybrid modules) - what once needed to be large specially trimmed items now have their specs bettered by small laser trimmed ICs. That's not to say that they don't still have value, but it becomes whatever people are prepared to pay for them. Some ICs in ceramic packages are unavailable or are only available in smd epoxy packages which have poorer long term stability (looking at the AD7846 DACs and AD588 references as an example), but price depends on temperature coefficient specs - the AD588AD for are the mid spec +/-3ppm/'C max parts, stable, and ceramic, but not quite as sought after as the BD spec for instance. You can definitely find these on ebay in new condition, but need to compare datasheet specs and new vs salvaged.You do need to factor in the fact that the parts in the first three photos are 20+ years old, and the ones in the last two, around 40 years.Yes, I would go ahead and take more photos and see what people are prepared to offer - Again, I think you will do better with interesting and untouched boards than you will with unsoldered and untested components. Even if you did have the (considerable, not just basic DMM and scope) equipment and capabilitied to test them, you wouldn't make a return on your time and effort.P.S. I haven't seen anything yet that grabs my personal interest (I already have a stock of AD588s!), so hopefully this counts as reasonably impartial advice.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 14, 2022, 02:17:36 pm
content: Maybe it's relatively easy to test functionality of some of the circuits on the original PCB. for example checking the output voltage of a voltage reference should not be too difficult if you've got a DMM with adequate resolution.I would not start desoldering IC's from these PCB's. Selling the PCB's whole, or maybe cut them in half if they've got a lot of valuable old IC's is probably preferable.

author: radiolistener
author_rank: Super Contributor
timestamp: July 14, 2022, 07:31:40 pm
content: you can power on the device and see - if it works then IC is working

author: Gyro
author_rank: Super Contributor
timestamp: July 14, 2022, 09:00:51 pm
content: Quote from: Doctorandus_P on July 14, 2022, 02:17:36 pmOuch! I can't see that doing much for the value of the ICs.

author: jorgeh
author_rank: Regular Contributor
timestamp: July 15, 2022, 07:57:54 am
content: jajaja ehhmmm that would be beyond my capabilities. i mean sure I can turn the device one. but one is a guided missile launcher test equipment, others are from an atomic force microscope. an old weather station, airplane fuel test equipment, . besides seeing if the lights turn on i cant do much about it.