Wednesday, April 13, 2016

Counterfeit 2N3055 Transistors from eBay

I recently needed some 2N3055 TO-3 transistors for a project, but could not locate any around my basement, so I went ahead and carefully purchased some from eBay. I'll explain what I mean by carefully, a little back story on this before I continue.

Counterfeit 2N3055 Transistors vs Real

Counterfeit components sourced from eBay is not a new thing or a surprise. I don't think that I would be wrong in saying that most components on eBay are a no-name brand from Shenzhen, if not actually counterfeit. Now if you know what you are looking for specifically and don't just buy the first thing that pops up in your search results, you will be fine. Plenty of components from China are just fine, LEDs are a good example. I have LEDs of probably every wavelength available in bags by the hundred that cost next to nothing from China, all from eBay. Many have been used in projects running for years without issue, for items like this I have no issues with cheap components. But when I'm expecting a legitimate transistor sold as a name brand, and get a knock-off cheap piece of crap there is an issue. As I have learned, TO-3 transistors for whatever reason are a very popular thing to counterfeit.

So back to buying my transistors. Fake transistors are usually easy to spot visually. The cases are always shiny, the label on the case is usually crooked, or blurry from the poor printing process that is used. The type fonts are often weird. They just look cheap. So I first picked a few ST Micro 2N3055s that in the auction picture looked like original OEM transistors comparing to other TO-3 style transistors I had around. This was from a US seller with a good reputation too, everyhting looked legit. I had them in a few days, what I received though was not the same transistor shown in the picture. It looked wrong, it felt wrong, everything was just wrong about it. I purposely avoided all of the listing with transistors that looked like this as I knew they were counterfeit but ended up with them anyway.

To test for a counterfeit transistor, first just see if you can rub the label off with your finger. The label on this transistor came off with little effort just by rubbing on it. A stronger test is to use some rubbing alcohol, a real transistors label will not come off even with alcohol. Also look at the date codes, most counterfeit transistors will have a misleading date code or just be non-existent altogether.

So at this point I knew they were crap, time to crack one open. Stick it in a vice and with a couple taps of a hammer on a chisel right on the lip of the edge, it popped open with barely any effort. What is inside is comical:
Counterfeit ST 2N3055

A tiny little die glued down with some white stuff and tiny little bonding wires, really pathetic. My favorite feature is the surface rust seen on the inside of the can. I wonder how long this case was sitting around before someone manually assembled it.

For what it's worth, I did test the transistors and they do work, although I highly doubt they will handle the current they are rated for. Based on this discovery I was curious to see what else I could find. Could I get any real new 2N3055 transistors on eBay? To find out I went back on eBay, found another set of this time Toshiba transistors, the most legitimate listing I could find that was not labeled as NOS or used. It was a similar auction, US based seller with good rating, transistors are claimed to be OEM. After receiving, they again are different from the picture and just wrong:

Counterfeit Toshiba 2N3055

The ink rubbed off on this one just as easily, the can popped off almost with no effort. There in fact wasn't even any damage to them when I removed it, a clean break. And inside, this one was even better. Similar construction, and the bonding wires! Oh my, even smaller than the previous labeled ST transistor. At this point I could keep buying them seeing if I could find anything legit, but I decided to cut my losses and just get the real thing.

As a final comparison of what this transistor should look like, I purchased some legitimate ON Semi 2N3055s from Digikey. They were only about a dollar more a piece than the ones available on eBay. After receiving, a noticeable difference is noted right away. Most importantly is the weight, they feel much heavier. Also the labeling, you can rub them with alcohol and the label does not come off at all. I decided to sacrifice one (which did not come apart very easily) and you can see the obvious differences on the inside:

On Semi 2N3055

First big difference is the backing plate. The die is mounted directly to a piece of metal designed to better distribute the heat off of it and down to the case. Next is the die itself, noticeably larger than the other transistors and it is better mounted to the backing plate, not a big dab of white adhesive. Finally the bonding wires, they are considerably thicker than the other two transistors. Here is a close up comparing each transistor:

I ended up contacting the sellers of the transistors from eBay just to see what their response would be in telling them that their components are most likely counterfeit. One seller actually seemed to care and began questioning his supplier, whether or not he actually will do anything about it is yet to be seen, the transistors I bought are still available by him. The other seller didn't seem to care at all and simply said I could return them if  I didn't like them. I will also note that all of these transistors did work, although I have not tested them at higher currents which is where most people say they will fail. Either way I don't trust them and wouldn't use them in any serious project. It seems the counterfeit market for these is much worse than I had expected.

Thursday, April 7, 2016

HP 54503A NVRAM Replacement - DS1235YW to DS1230Y

A few weeks ago I turned on my HP 54503A to find it behaving strangely. While probing a circuit under test, I could not get any waveforms at all. Was very unusual, so ran a quick self test and was greeted with the following:

HP 54503A Selftest Failure - Protected Non-Volatile RAM

This didn't look good.  An important key to the cause of the failures was the failure of the Non-Volatile ram. Most older equipment like this used a Dallas Semiconductor real time clock / NVRAM IC to store the calibration data along with waveform storage. In this case it is not a real-time clock, just a battery backed DS1235YW RAM ic. This classic chip has an internal battery to backup the contents inside, technology that existed way before inexpensive flash memory that has a limited lifetime. Based on the manufacturing date on the late 1980s, this ic was almost 30 years old, way beyond its expected lifetime but about average for how long I see these devices last.

The HP 5450NA family of scopes 54501A, 54502A, and 54503A are really nice scopes readily available for cheap. My favorite part about them is the interface, it is intuitive and lightning fast. Response from button inputs is instantaneous, unlike many modern scopes which makes it a pleasure to use. This was definitely getting repaired.

A quick way to check to see if the NVRAM is indeed the issue is to flip the write protect switch on the back of the unit off and attempt calibration. Once you calibrate this scope, you flip this switch to protect the contents from accidental writing, but in this case I want to re-calibrate it and to do so you must enable writing. Once this switch was changed I ran the calibration procedure for channel 1. It calibrated successfully and brought the scope back to a working state. So this was the only problem and the NVRAM ic will need to be replaced, unless you feel like going through a full calibration every time you power the scope on. Since a full calibration of all channels takes around 25 minutes, this is not ideal.

HP 54503A Main Board

This scope comes apart very easily, the main board slides out of the back with little effort. Once removed the Dallas NVRAM was easy to spot:

HP 54503A DS1235YW

Removing this ic is pretty easy, use a nice fat hot iron and some fine solder wick and the ic falls right out with no damage to traces.

HP 54503A NVRAM Removed

As far as a replacement, the original DS1235YW is not easily available, but the pin compatible DS1230Y is available. It is still made and Digikey sells it for $30. Then there is the eBay source of them direct from China for only $5. While the Chinese version is guaranteed to be a knock off, it does work as I have used them before. I went ahead and used one for this replacement since I have a few laying around.

There are also available pin compatible flash based alternative ics that you can use in this scope, but I have never personally tried them. One last note is as long as you are going through the trouble of this, go ahead and place a socket on the board so in the event your new NVRAM doesn't work, you won't have to stress the board with another de-solder. Here is the replaced ic:

HP 54503A DS1230Y NVRAM

Once replaced and everything is back together, calibration is the last step. Set the write protect switch to off and run through all the calibration procedures. The calibration for this scope requires a 50ohm bnc cable to be fed from two outputs on the back of the unit to each channel is sequence, the scope really walks you through everything. The manual will explain all of this as well, but is really a simple procedure and a really nice feature.

HP 54503A Calibration
When done, set the switch back to write protect, test it out and power cycle it to verify all calibration was held. Good as new.