View Full Version : How to safely probe a sound card with a multimedia speakers 3.5mm headphone jack?

retro games 100
January 7th, 2012, 11:39 PM
I am trying to find out why an old 8-bit Adlib sound card does not produce any sound. I want to probe this sound card, to see if I can hear any sounds from it. I need to find out how to do this safely. Will the following idea work?

Get 2 crocodile/alligator leads, one red, and the other black. (Actually, the colour of the leads may be unimportant.) Attach the black croc lead clip to the ground sleeve section of the speaker's headphone jack. The other end of this black lead goes to the black ground part of a PSU molex cable. Now, get a red croc lead, and attach it to the very end of the speaker's headphone jack. The other end of this red lead is used to probe the Adlib card. Is that correct? Thanks a lot for any advice.


January 8th, 2012, 10:31 AM
I would do this instead:

Get an amplified speaker; between the tip of the input plug connect an 0.01 F capacitor and one end of your probe lead. Connect the ground sleeve of the input to the chassis of your PC. Probe away--you should have sufficient isolation not to bother anything that you probe.

retro games 100
January 9th, 2012, 01:03 AM
Thanks a lot Chuck. I posted a reply to your message over 12 hours ago, but it never appeared. I'll try again..

Looking at the image below, is this what you mean? What is the best way of holding one of capacitor's legs to the tip of the headphone jack? Can I use a croc clip (with a lead attached to it)? I searched on ebay for capacitors, and found many different listings. I picked one at random. It's here (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=290581428670). Would these work? This listing is for 0.01uf green mylar 100v capacitors.

Finally, on the "probe end" of the red croc clip, which is the one used as a probe on the sound card, can I put a thin/fine piece of metal in its "mouth". For example, a paperclip. This is to make the probe part of the red croc clip small and fine, as opposed to a "fat and closed" croc mouth. Thanks a lot for any help on this.


January 9th, 2012, 07:55 AM
Yup, that's what I mean. The idea is to thoroughly isolate the speaker-amplifier so that a probe to a wrong place won't do any harm.

retro games 100
January 10th, 2012, 08:29 AM
Success. The "probing method" outlined in the posts above has worked. This probing method has allowed me to determine that the headphone connector may be faulty, because I could hear music when I probed all relevant solder spots on the Adlib sound card. Someone on a different website (Vogons) has suggested that I buy a mono headphone adapter plug, just in case the headphone connector on the Adlib card does not support a stereo jack. Also, please note that the capacitor I used was rated 1uf.

Edit: I've just been told not to use a mono headphone adapter plug, because the Adlib card outputs its sound in stereo.

Edit 2: The problem with the Adlib sound card has been solved. The reason why no sound was coming out of the headphone connector, was because the top part of this connector was not fully secure, and so when the headphone jack was pushed inside the headphone connector, it wasn't making a secure contact.