I hope someone can help I am trying to find out what this component is so I can hopeful replace it

The device is a Fluke Network Management device

the unit works for about 2-3 minutes depending on temp then gives out a high pitch squeak the unit keeps flashing looks like there is life but the unit stops responding I first thought it was the PSU from where the noise was coming from

I striped the unit down set it up on my desk plugged it all back in and waited the noise not sounds to come from the main board in the photo it is where a second board plugs in and the power supply comes from

All the but has on it is 8Y I have looked high and low the best I got to was a 3 pin transformer or a rectifier but not 4 pins plus I'm not sure if the specs are the same or if its a transformer or a rectifier

I am going to pull some none working devices apart to see if there is one in something else

enter image description here


I have not received very much from Fluke nothing from technical

So to get things moving I have removed the part not the cleanest of removals but I just sniped it off enter image description here

It looks like a common mode choke with help from people on here to me but its the values of it that I'm not sure of, is there any way to work it out the unit will take 100-240 VAC 47-63Hz 25 Watts not sure if this helps

would this be a replacement TDK ZJYS51R5-2PT Choke

I've got nothing to loose the unit stop working after this bit gives a high pitch noise

If anyone can help me would be good


  • \$\begingroup\$ Common mode choke maybe, guessing by the packaging, and the T**** ref des. \$\endgroup\$ Commented Apr 22, 2015 at 20:44
  • \$\begingroup\$ IT most likely is some kind of diode, look up all possibilities on search engines like smdcode.com \$\endgroup\$
    – PlasmaHH
    Commented Apr 22, 2015 at 20:44
  • \$\begingroup\$ Thank you for everyone's answers this looking like a mine field its could be a common mode choke I have found 4 pin ones that look like they will fit, Fro the advice above I have looked up 8Y on smdcode.com and found one SSOT-24 Linear voltage regulator integrated circuit 4 pin looks like it could be ??? is there anything I could do to work out what it is, I will try to contact Fluke see if I can get schematics these my help? \$\endgroup\$
    – Petery
    Commented Apr 22, 2015 at 22:08
  • \$\begingroup\$ I just want to add that it is very, very unlikely that a common mode choke is the failed part, because it is nothing more than a piece of wire. More likely, you heard a noise from it because something in the rest of the power supply circuit has failed, or a component has failed short, and the ripple current is high as a result. \$\endgroup\$ Commented Apr 30, 2015 at 23:27
  • \$\begingroup\$ Hi, Thank you for the replay would it make any difference if I explain that that first there is the PSU then this connects to a board with 2 of these one then the board connects to the maim board that has 3 of these? would it help if I have noticed when trying different things the problem happens sooner if I have both of the Ethernets plugged in (management and monitor ports) ? how would I find the values because I will have to get a new choke now anyway I mite be able to solder it back on I can see your point they work to keep thing stable but something before it maybe the problem \$\endgroup\$
    – Petery
    Commented May 1, 2015 at 10:51

2 Answers 2


The board designators seem to be following IEEE STD 315 (kind of).

CR or D: Crystal rectifier (Diode) T: Transformer.

My guess is that this is a common mode choke on the power supply lines.

  • \$\begingroup\$ Hi thank you for your answer having looked online this sound highly likely to be a common mode choke as you say \$\endgroup\$
    – Petery
    Commented Apr 22, 2015 at 21:50
  • \$\begingroup\$ if I was to try to get hold of one from a auction site or any other site what would I be looking for I have looked for common mode choke found a TDK ZJYS51R5-2PT would this be a good replacement I do not know much about these things (I have played about with simple stuff) what to look for spec wise I know there is not much to go off from the bit its self would it help to unsolder it and see if there is anything on the bottom? \$\endgroup\$
    – Petery
    Commented Apr 22, 2015 at 21:55

It's a audio transformer/isolator, compare this picture:

Link to the component: https://nl.aliexpress.com/item/5PCS-1-1869FH-60UH-1-1-SMD-digital-audio-isolation-transformers/32432427615.html

No idea they use it that way for audio but these components are also found in modems etc.

enter image description here


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