Any issues with this adapter? - Page 1
Forum section: electronics / beginners

author: giosif
author_rank: Frequent Contributor
timestamp: November 07, 2020, 01:28:20 pm
content: Hi,I've built the adapter in the below pictures and I'm getting rather mixed results with it.As such, I am starting to wonder if the length and layout of the cables might create problems here, but I am not sure.Do you think my concerns are valid (e.g. cables overlapping causing cross-talk, cables being of different length introducing unequal signal delays)?Thanks!

author: Gyro
author_rank: Super Contributor
timestamp: November 07, 2020, 02:17:04 pm
content: That depends entirely on what you are using the adaptor for. Frequency and rise/ fall times of signals whether it is digital, analogue, video or some sort of mix. It's impossible to say otherwise.One thing that does stand out immediately is the lack of supply decoupling capacitors (hopefully to a solid ground) for whatever device you're putting in the socket.

author: giosif
author_rank: Frequent Contributor
timestamp: November 07, 2020, 03:54:50 pm
content: Indeed, I should have mentioned what the adapter is intended for: I am trying to read and program some PLS155 and PLS159 ICs.For the supply decoupling cap, what capacitor value would you suggest I use?

author: JackJones
author_rank: Regular Contributor
timestamp: November 07, 2020, 04:02:37 pm
content: What kind of problems exactly are you having? Intermittent dodginess?Some of the solder joints look a bit crusty to me, that could very well be the problem.

author: Gyro
author_rank: Super Contributor
timestamp: November 07, 2020, 05:47:51 pm
content: Quote from: giosif on November 07, 2020, 03:54:50 pmAh ok. If you're trying to read the devices with a programmer, then it will hopefully be trying to read out quite slowly. I'd suggest something around 10-100nf wired directly between VCC and GND across the back of the socket. Also beef up the GND connection if possible.It can be very hard to read pre-soldered parts, you get lost of build-up of flux residues on the socket contacts (I can see lots of fibres and crud in the photo). You really need to give the devices a short bath in IPA, and flood the socket to clean it up too.

author: giosif
author_rank: Frequent Contributor
timestamp: November 07, 2020, 06:32:34 pm
content: Quote from: JackJones on November 07, 2020, 04:02:37 pmI was able to read one PLS IC and its contents were exactly as expected.A few days later, trying to read the same IC, I got all 1's.Quote from: JackJones on November 07, 2020, 04:02:37 pmI will touch up those joints.

author: giosif
author_rank: Frequent Contributor
timestamp: November 07, 2020, 06:36:33 pm
content: Quote from: Gyro on November 07, 2020, 05:47:51 pmOk, will do that.Quote from: Gyro on November 07, 2020, 05:47:51 pmI am indeed installing de-soldered ICs in that socket.However, I always clean them up with IPA after de-soldering them.But you are right the socket looks it needs cleaning, so I will do that, install the cap, and then try again.Thanks!

author: Photoman
author_rank: Regular Contributor
timestamp: November 08, 2020, 02:04:01 am
content: A problem I recently ran into with PLCC sockets might relate to your issue.The sockets pins, after only a few insertions/removals had bent away from the chip.That caused all sorts of fun from no connection to an intermittent connections on some pins.I made a little tool out of a long pin header to gently bend them back in line.

author: giosif
author_rank: Frequent Contributor
timestamp: November 08, 2020, 10:59:16 am
content: Ok, so an update on this:- I added a 10 nF cap between VCC and GND- I added a second wire for the GND connection- I cleaned the IC socket with IPA- I cleaned the pins on the ICs using an eraser first, then with IPAYet, trying reading the ICs, I got the same results.But, then, I was saved: @Photoman, you were completely right.It turns out the ICs were not making good contact with the socket pins, when pushed all the way in the socket.I feel so silly (just to avoid saying "stupid") I just refused to consider that as a possible cause (had crossed my mind at some point, but only for a femtosecond).And, now that I think of it, I had encountered this issue in the past, where the PLCC IC would not make good contact with the socket pins and had to use a shim to raise the IC in the socket ever so slightly.That is not to say that the above suggestions on cleaning the contacts, using the bypass cap and reinforcing the GND connection were not needed.So, thank you everyone for you help!It is very much appreciated.