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| Fake chip verification? |
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| bitman:
I think I've got my first "real" set of fake chips from Ebay. Trying to build a plugin debugger for a 7400 IC CPU I needed something to quickly show/decode binary to hex - and the old DM9368N seemed to be it albeit nobody really had it at a reasonable price. I did find it on Ebay - not cheap but not at $20 a piece either. https://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/DM9368.pdf just for reference. The chips are labeled with HP1901Y in addition to the model number. I cannot find any public datasheets with HP as a manufacturer of these chips. I guess there's a chance they used the DM9368N for something different? However, now that I'm trying the chips I received on the prototype board things aren't working. First, I've tested 3 chips and they all seem to behave slightly differently. One doesn't draw any current regardless of what I do to it. Others will look like a short (or close to it) but simply pull pin 3 (LE) high or low. Strangely when you remove the connection it stays high current - the chip gets very hot and well at that point I disconnect it. Since I'm getting different results and I can rub off the printing with a bit of Isopropyl Alcohol, it also doesn't seem to do any kind of current limiting on the outputs I am concluding this is a fake. EDIT: Above paragraph rephrased to make sense. First, I'm pretty sure whom-ever sold me this will deny and won't care. I'm not looking to convince him/her but more to to learn if I can trash these ICs or if I should keep on trying. From what I can see the pins aren't doing what the datasheet says they should. A "Latch Enable" should definitely not short anything regardless of setting. In particular since only gnd and vcc are connected when it happens. Of course when a chip doesn't seem to have any functionality that also indicates "bad chip" to me. I found on youtube a hint to use the Isopropyl Alcohol and that at least looks like it could be a good indicator. Sad part is I bought other chips from the same vendor I haven't tested yet so now I think the whole batch may be DOA. Now, this is definitely old technology - so if there's a better way to drive a dual 7 segment display using BCD that actually displays HEX and not those weird characters that most 7400 chips use, I'll gladly consider changing my design - in particular if those chips are cheaper and more available. It would really be great if it was current regulating too. |
| wraper:
--- Quote from: bitman on March 01, 2020, 11:09:53 pm ---The chips are labeled with HP1901Y in addition to the model number. I cannot find any public datasheets with HP as a manufacturer of these chips. I guess there's a chance they used the DM9368N for something different? --- End quote --- No photo provided and I don't think this marking has anything to do with HP. |
| bitman:
--- Quote from: wraper on March 01, 2020, 11:29:22 pm ---No photo provided and I don't think this marking has anything to do with HP. --- End quote --- Well, I can fix that. Doesn't look like an HP logo at this angle so you may be on the right track. |
| syau:
You may consider to try 74C925. |
| oPossum:
That is the National Semiconductor logo. For some alternatives see this thread: https://www.eevblog.com/forum/projects/16-bit-to-4-digit-7-segment-decoder/ |
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