If you follow Yet Another (Discrete) Clock, you know this project uses quite a lot of MOSFET in the easy-to-solder TO-92 package. A bit less than 500, including about 300 N-FET (BS170 or 2N7000) and the rest are P-FET (BS250).
The N-FET are OK: I could source 300×2N7000 for around 10$, 3 cents per piece is a nice deal and a decent price for the project.
The P-FET are another story :I could find cheap reels in SOT23 but the prices are much higher for the TO-92 package and there seems to be a sort of shortage in the usual cheap markets. Earlier this year, an order never made it to my home (among other postal problems) and a 200pc lot was found to have a reverse pinout (https://hackaday.io/project/9376-yet-another-discrete-clock/log/37927-it-was-too-easy).
This post is about another escalation in the BS250 horror story. I found a decently priced lot of 100 on eBay (due to Brexit) and this time ordered only one lot (I was not feeling rich, and at 20GBP, or about 24€ for 100, the unit price is almost 10× higher than the N-channel). Since the precedent lot (2×100) was functional (despite the reversed pinout) and was delivered, I bought from the same seller. Delivery was pretty fast (maybe due to summer vacations and less business) so I was ready to leave another good feedback.
Just to be sure, I tested a few parts from the bag. I don't remember why but you never know, and I wondered what was the pinout this time. Guess what ? I found a MOSET but in N-channel, not P. WTF ? It's marked "BS250" !
I take another then another and start to find a "mixed bag"
- Some parts are indeed P-channel but a minority
- Most are N-channel
- Some weird arrangements, like dual diodes, or very malformed junctions
- The surface of several packages look altered, like attacked by acid, and a couple have no marking. Others have a different style of marking...
After I sent a complaint to the seller, I received the following:
« Hi,client.So sorry for your trouble.Could you let me know how many
pieces are not working as excepted,I will check with our supplier for
this issue.Regards, Namedeleted »
Wait, you send me worse-than-counterfeit parts then you want me to do your job, for which I paid you ?
Alright, since you wanted it, let's waste 2 hours testing all the parts by hand.
I could identify:
- 25×P-channel (more or less BS250, I only tested the simplest parameters)
- 61×N-channel (some sort of 2N7000 but I didn't care about the pinout)
- The rest are malformed, non-functional parts.
Only 1/4 of the order can qualify as conform.
Pictures to come...