Heathkit IT-1121 WRAPPED IN STATIC CLING WRAP ... Help! - Page 1
Forum section: electronics / testgear

author: innkeeper
author_rank: Unknown
timestamp: September 13, 2018, 07:51:07 pm
content: I bought a heathkit transistor curve tracer off eBay. I guess the seller thought it would be a good idea to wrap the whole thing in static cling wrapSo now how can i get this stuff off without generating a hell of a lot of static electricity and basically destroying the components in the curve tracer?

author: SeanB
author_rank: Super Contributor
timestamp: September 13, 2018, 08:09:04 pm
content: Cut it, and as you are unwrapping just have a spray bottle with some water that you mist the plastic with, and wipe with a damp cloth regularly. This will handle the static quite well.

author: innkeeper
author_rank: Unknown
timestamp: September 13, 2018, 08:30:51 pm
content: hmm... i like it, I'll give it a try

author: Specmaster
author_rank: Super Contributor
timestamp: September 13, 2018, 09:11:33 pm
content: I was going to say the same as SeanB but add to do it on an antistatic mat as well.

author: Wolfgang
author_rank: Super Contributor
timestamp: September 13, 2018, 09:16:13 pm
content: ... these pieces of equipment came from an age where static sensitive components were hardly every used in kit equipment.They knew why

author: innkeeper
author_rank: Unknown
timestamp: September 13, 2018, 10:43:38 pm
content: so that worked perfectly... and yes I used an anti-static mat as well. zero static issue!SeanB and Specmaster thanks!in case anyone might be thinking it was a non-issue...I knew this was a potential problem as the person had shipped me a wrong item earlier, A tv sweep gen which was wrapped the same way. I didn't give much notice to how it was wrapped as it was gonna be returned and swapped out .. but it turned out the item was worth less then the shipping would have cost so he told me to just keep it. upon tiring to unwrap it I was getting shocks from the metal case and my hair on my arm was standing on end as I unwrapped the cling wrap.. so it was obviously normal static cling wrap not the anti-static stuff ... by the time i unwrapped the sweep gen he had already shipped the curve tracer so it was too late to ask him not to pack it like that.I did contact the seller and explained why not to do that, but it seems he had 30 years of experience doing it this way and claimed never to have had an issue.don't get me wrong, they are an excellent eBay seller and corrected the miss shipped item immediately so not complaining about the seller. Id just not have used static cling wap myself.I've seen the pink wrap on electronics before, and have occasionally used it.. but never plain static cling wrap. I've mostly used the anti-static bags or the conductive bags myself.Quote from: Wolfgang on September 13, 2018, 09:16:13 pmyea I kinda was thinking the same thing, so before I got to concerned I looked at the schematic and saw a 7400 series device and a couple of 741 opamps and a 301 opamp and 3 small signal bipolar transistors that are no longer being manufactured..... so thought id better be safe than sorry. not that the circuit is that complex to troubleshoot. I didn't wanna add any more problems to it then it might already have. The device came in as is / untested condition, so if it works 100% that's a bonus, but I am not expecting it to work perfectly.. but still, no point in adding problems.

author: Wolfgang
author_rank: Super Contributor
timestamp: September 13, 2018, 10:50:13 pm
content: Congrats !Today, they even have ESD specs on a 2N3055. Its just a CYA (cover your ass) marketing trick if something goes wrong.The old stuff never had (and needed) any of this. Still, its better to be on the safe side.

author: Mr. Scram
author_rank: Super Contributor
timestamp: September 13, 2018, 10:53:24 pm
content: I suspect much of the damage done would have been done during wrapping anyway.

author: innkeeper
author_rank: Unknown
timestamp: September 14, 2018, 01:27:48 am
content: Quote from: Mr. Scram on September 13, 2018, 10:53:24 pmhmm maybe...well too late now to do anything about thatI did take a quick peek at the insides ... screws look like they have been out a few times. but otherwise totally clean..looks like it was built and never used. I found a few unsoldered connections already. and as you would suspect, gummy pots and switches. this should be a fun little thing to restore.too bad someone recently did a repair video on one of these, I can tell it would make a good repair / restore video.

author: innkeeper
author_rank: Unknown
timestamp: September 14, 2018, 02:11:45 am
content: well, I don't see any ESD protection in the it-1121 schematicalso, it is circa 1974 ish ... so ...~45 years old... it is an early serial number. I'll have to find some date codes.

author: akimmet
author_rank: Contributor
timestamp: September 14, 2018, 02:04:40 pm
content: Quote from: innkeeper on September 13, 2018, 10:43:38 pmNone of the components you mentioned I would have considered susceptible to ESD damage. I would have certainly been concerned if I have seen some 4000 series logic or MOSFETs however.I also highly suspect if a certain piece of equipment could be damaged from the removal of cling wrap, it was already damaged from applying it in the first place.Quote from: blueskull on September 14, 2018, 01:42:51 amUnfortunately this is not an entirely fair comparison. Quite a few '70s era designs actually were susceptible to damage, because proper input protection techniques weren't common knowledge yet.

author: innkeeper
author_rank: Unknown
timestamp: September 14, 2018, 08:13:20 pm
content: Ah well...so call me over paranoid lol....still, I don't like tempting fate with static discharges when it can be avoided.

author: Wolfgang
author_rank: Super Contributor
timestamp: September 14, 2018, 09:17:25 pm
content: Caution is always OK, but I would like to initiate a SN7490, LM741 and LM301 ESD damage competition. I am just curious how sensitive these old bipolar parts really are.My guess is way above 10kV. Any bets to the contrary ?

author: chris_leyson
author_rank: Super Contributor
timestamp: September 14, 2018, 11:04:48 pm
content: QuoteNope, not yet anyway. I used to buy 7400 or 4000 series parts and bipolar op amps (sometimes jfet) packaged in a piece of expanded polystyrene in a polythene bag. I would be standing there thinking WTF! no anti-static foam although the 4000 series parts had aluminium foil wrapped around the polystyrene. I never had any problems and all the parts worked OK. Poor anti-static packaging is not the same as a human body model static dischage.For example, if you stuff an IC into a piece of expanded polystyrene then it's likely that both parts will be at the same potential simply because you have "the part" in one hand and the "packaging" in the other, both at the same potential.The same probably applies if you wrap something in cling film, they are more or less at the same potential, the part you are wrapping is "grounded" throught the table or floor and the cling film is "grounded" through the wrapper. The ground connection could be 10s of Mohms but that is enough to bleed away any built up charge.Anyway back to the human body model and static. Lets say a human body could be modelled by a 100pF capacitor for sake of argument and you can pick up lets say 1kV by walking across a man made fibre carpet. In terms of available potential energy that's 50uJ. If you were charged up to 10kV than that would give an available potential energy of 5000uJ or 5mJ. It's the energy transfered into a part that is going to do the damage and the amount of energy required will vary depending on the semiconductor fabrication.Did you ever get an electric shock from unwrapping something covered in clingfilm ? Use a bit of common sense.

author: Wolfgang
author_rank: Super Contributor
timestamp: September 14, 2018, 11:19:02 pm
content: ... all agreed, but for a competition we need some well defined criteria.I suggest its either HBM or MM, whatever.I increase my bet to 15kV for both.