Damaged LNK304GN - suspicious fake replacement part?
Hello to those on this forum.
I have an appliance to repair which had a fried LNK304GN (correction - not GP) plus a couple of resistors.
Having replaced the parts, the unit failed to power up, so some further investigations were necessary. I was able to find an identical appliance (coffee machine) to make comparisons.
The short story is that I suspect the replacement 304s are incorrect due to a very basic test measurement. I even ordered a further 2 from a different source and these also - although stamped differently - measure incorrectly on the bench. And with this incorrect measurement it's clear these devices will never work in-circuit. Basically they measure short-circuit from BP (pin 3) to S (pins 7 AND pin 8). And in-circuit all 4 Source pins are of course linked.
And just to clarify, the working circuit measures high resistance from BP (pin 3) to the S pins.
This is 100% a G package not the D package.
Can anyone offer their thoughts on this?
The fried board is here.
The replacement 304 is here.
304 pinouts here.
If these are dud parts then how to order a genuine part?
Appreciate any input.
Thanks,
Steve
Comments
Thank you very much for your response and information.
I incorrectly stated it was a GP when it is a GN on the original board (I correct the post above). Here are 2 images of the fried GN and in #1252 you can GN stamped on the body.
Appreciate your further feedback on this very confusing situation.
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| IMG_1253.LNK304GN.fried_.jpg | 86.44 KB |
| IMG_1252.LNK304GN.fried_.jpg | 80.61 KB |
Hi stevepeck17,
Thanks for the correction.
Just to clarify:
- Did you measure the BP-S pin off-board (unsoldered) or on-board (soldered)?
- Was the working circuit measured before or after the damaged occurred?
- Were you able to replace potentially damaged components? It is possible that there were other damaged components that results to the shorted BP-S pins you mentioned.
Also, were you able to measure the pin resistances previously suggested? Note that those values were measured while the IC is not soldered on the board (off-board).
It will also be a great help if you can provide a schematic of the circuit to help in troubleshooting it.
Thanks and regards,
Hello again and thank you for your further response.
I have done detailed measurements of 2 ICs to all pins off-board. These are newly ordered components:
And to clarify this statement I made previously, this was an in-circuit measurement:
And just to clarify, the working circuit measures high resistance from BP (pin 3) to the S pins.
I stated this above because in-circuit all S pins are common (1, 2, 7 & 8). This proves that in a working circuit there is no S/C (as expected) between BP & S.
To me, the measurements that I am getting do not correlate to the device I'm expecting to test when I relate my pinouts to the PI data sheet. It's as I'm comparing a different device. And yet I've purchased these from 2 different (random) suppliers.
Your measurements to all Source pins would be of particular interest.
I did also replace the 2 burnt components (both were resistors) plus the IC. No other components appear damaged.
I've hand traced the circuit during my diagnostics and will have to draw them better on the computer and post it here.
Thank you very much for assisting.
Adding the schematic here as requested.
FYI: it was R2 & R3 that were replaced and had burnt.
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| LNK304GN power circuit.png | 28.08 KB |
Hi stevepeck17,
Thanks for the added information.
About the resistance measurements. Can you also measure the 3 pin combinations (BP-S, D-S, FB-S) I tested? Measurements are usually referenced to the Source pin (negative probe).
In addition, can you check if other components along the input side (i.e. diodes) are internally damaged, in addition to R2 and R3? If you could remove them from the board first before individually testing them to see if they are still fine.
Lastly, if you can isolate the power supply from the load and then test it just to see if there are no problems on that setup.
Thanks and regards,
Thanks for your message.
The resistance measurements that you ask for: exactly which S pin are you referring to?
My measurements (off-board) suggest these are not electrically connected within the IC (except p7 & p8) so I am getting different results from different S pins.
If you can please confirm.
Thank you.
Hi stevepeck17,
Good day. Since you are getting a different reading on what we might expect from the device, we suggest that we proceed in reaching out to our sales team to confirm your parts are indeed genuine. Please log in a request through the form in the link below.
Sales Inquiry | Power Integrations, Inc.
All the succeeding actions will be taken offline. Thank you and we hope the problem gets resolved the soonest.
Regards,
PI-Gavin
Thanks PI-Gavin - I will log a request using the link you've provided.
Thanks again for your assistance on this topic so far.
Regards,
Steve
Hi stevepeck17,
Thanks for using PI product.
I also checked the resistance of the BP-S pins, and also other pin combinations. For your reference, below are the rough values I measured using several LNK304GN:
With that, may I clarify if the original part is LNK304GP? I can only see LNK304GN as the available part. I'm trying to check it with the Fried Board photo you gave but I can't seem to distinguish it from there, assuming it's the original part there.
Thanks and regards,