Experiment: buying obscure obsolete IC via chip broker

[TerraHertz]

Recently I repaired a power supply in a HP 54120B mainframe. It's part of a HP 54121T 20GHz scope system.
A writeup of the repair is here: http://everist.org/NobLog/20151112_planning_vacuum.htm#54120B_ps
Incidentally, the full schematics of the HP 54120B power supply and backplane are there too.

For a while I thought the fault was with a switch-mode control IC, that the parts list has no information on other than a HP part number: 1826-1120. The chip is marked with that number, plus an Exar logo.

It turns out this part is unobtainium, and has a total lack of information to be found on the net. That number is skipped in all the HP equivalent parts lists I can find. Nothing online but other people begging for some info or source to buy them.

With one exception. I found a parts broker web site, that listed several sources claiming to have stock. LOTS of stock.
http://www.digchip.com/datasheets/quote.php?action=search&pn=1826-1120  (see pic)
For an obscure, long-obsolete part with no data available (that I can find) I'm surprised by the quantities they claim to have.  Are those believable? I suspect not.
Has anyone here ever used this service? I never have. Does it work?

So this is the experiment. I submitted a request for quotes, from all the listed suppliers, for qty 4 of the parts.
Several email quotes came back within 2 days:
  Bonase   Electronics  bonasehk.com           $26ea, no postage spec
  New Strength Electronic  http://www.ic-trade.com/company/25970.html   $7ea   + $10 post
  Excellence IC exeic.com www.excellenceic.com  $15ea, no postage spec.
  HXD Electronics hxdic.net  $18ea, no postage spec.
  IC International  www.ic-international.hk  $20ea, no postage spec.
 
I replied to the New Strength $7 quote, asking a couple of questions. (Any known source of chip data? Are yours original cerdip?) They replied but did not make any effort to answer.

Rather than drag things out with people who probably don't read/write English much, I just sent payment (via paypal) for qty 2. They responded to acknowledge payment.
Now I wait.

I'll let you know how it goes. Is the whole thing a scam? Or are there really warehouses full of old obscure parts like this? I've no idea. Anyway, it cost USD 28 to find out. If this works, it would be great.

The power supply I fixed has three PCBs, and each one uses one of these ICs. I put in a socket for it on two of the PCBs, one of which is easy to remove from the machine. So if any ICs actually arrive, I can easily check if they work.
 

[all_repair]

The last round I bought some obsolete chips direct on Taobao.  First vendor, I bought 8 chips but he sent in 2 batches of 4.  All used.  1st batch of 4 were fake.  Then I rushed another order for new-old chips at a higher price from another vendor.   The 2nd batch of 4 turned up to be OK.  And the new chips turn up to be good also.  Fake obsolete chips are quite common.  The Taobao review system got me back the money, and the vendors were just broker that picked up the chips from the alley shops. 

[edpalmer42]

I had a similar situation.  I was trying to fix a device that used a chip designed by Stanford Telecom.  I later found that it was a semi-custom IC that was fabbed by Orbit Semiconductor.  Obviously, there was no second source for these and they had been out of production for many years.  I found a source on AliExpress, crossed my fingers, and bought a lot of 10 for about $50.  They turned out to be original, NOS!     Happy Camper!    Device is repaired and working fine - with spares if the chip dies again!

Ed

[cdev]

Those prices are not so high considering the cost of losing some essential, irreplaceable piece of equipment. This is good to know.

[Corporate666]

Bought from there several times.  As others have said, there are a few options....

-New old stock

-Removed from equipment (may or may not work)

-Fakes

I've seen a roughly even distribution of the three but that's with a tiny sample size.  It DOES seem, however, that you don't want to go with the cheapest price or with someone who doesn't answer questions.  It's usually worth paying more for a communicative seller who will tell you the parts are real (and you have that on your side should you find out they are fake and need to get your money back)

[nctnico]

I have a similar (positive) experience with buying custom oscilloscope pre-amplifier chips: I got brand new devices.

[TerraHertz]

Is it possible to nuke your blown chip with hot concentrated HNO3 and H2SO4 so to decap it, then use a microscope to reveal its real Exar/Sipex part number?

I don't have any blown chips. The one I initially thought was faulty (I had no circuit diagram then) was OK after all. See the story. Just buying two spares (I hope.)
But if I did want to open one, it wouldn't require acid. They are in those ceramic packs with the two slabs of ceramic glued together. Those can be cleaved apart, and the chip is in a cavity. Done that many times.
Date of manufacture would be around 1986 or a few years later.

It DOES seem, however, that you don't want to go with the cheapest price or with someone who doesn't answer questions.  It's usually worth paying more for a communicative seller who will tell you the parts are real (and you have that on your side should you find out they are fake and need to get your money back)

You are right of course. It's an experiment, so I started with the cheapest option. If they are not genuine, I'll try again. I do want to have a couple of these spare.

[TheSteve]

I used one of the chip broker sites to request quotes for the DDS ASIC from an HP 33120 AWG. Part #f107563fn, made by TI. I got a ton of replies, all priced about the same($50 USD). In the end I chose one that took paypal and replied to every email. They told me all of the dealers were buying from the same supplier and that the supplier had 3 of them, maybe the truth, maybe not but I suspect it was the truth. Anyway, DHL brought me the chip in 2 days and it was 100% real, brand new and it repaired the AWG. So while not as ancient as some parts the chip is technically unobtainium yet they got me one and it was totally worth it.

[Jay_Diddy_B]

Hi,

I think I have come across this chip before. At the time I was repairing an HP 54111D or 54112D oscilloscope.

I mention this because it may be another source for this part.

I can remember trying, unsuccessfully, to match the device to catalog parts at the time.

Regards,

Jay_Diddy_B

[janekm]

There's a useful website http://www.hqew.com which has access to the inventory of a lot of the small (mom&pop) and medium-to-large distributors in China. If you type in the number of an IC in the search field, it will show you a listing of distributors which carry that part, and their reported stock level. For example, AMS1117-3.3 shows up 1341 listings!

It's useful for finding out which chips are commonly available in China (scavenged or new) and which are not. Only one distributor reports having this chip, assuming the part number is the same... But it's reported to be PDIP20 so the odds are decent.

[amyk]

Exar made a lot of custom parts, including hybrid gate arrays. That might be what the HP part is.

I guess this is what happens when large stocks of parts are discarded by companies, sent over to China for "recycling". Those are the NOS ones. The used ones will be pulled from discarded equipment, and the fakes are going to be parts currently in high demand.

[janekm]

There's is actually a very vibrant market in used / second-hand test gear in China (not surprising I suppose... A decent Tech scope has a lot of value in a factory environment no matter the age). Dave would have a field day in the test equipment markets I'm sure whatever is "beyond economic repair" is stripped down for parts.

[TerraHertz]

There's is actually a very vibrant market in used / second-hand test gear in China (not surprising I suppose... A decent Tech scope has a lot of value in a factory environment no matter the age). Dave would have a field day in the test equipment markets I'm sure whatever is "beyond economic repair" is stripped down for parts.

I don't suppose that some of this vibrant 2nd hand market is in Shenzhen, and you'd have shop addresses you could post?
Since, I hope to be going there this year, and not reading Chinese it's difficult to search for such things.
Would be interesting to see, even if I'm not buying.

[janekm]

There's is actually a very vibrant market in used / second-hand test gear in China (not surprising I suppose... A decent Tech scope has a lot of value in a factory environment no matter the age). Dave would have a field day in the test equipment markets I'm sure whatever is "beyond economic repair" is stripped down for parts.

I don't suppose that some of this vibrant 2nd hand market is in Shenzhen, and you'd have shop addresses you could post?
Since, I hope to be going there this year, and not reading Chinese it's difficult to search for such things.
Would be interesting to see, even if I'm not buying.

Yes indeed I was talking about Shenzhen! I think it was in the building I marked on the map, on the second floor. Let me know if you do find yourself out here, we can have an eevblog meetup

[TerraHertz]

Yes indeed I was talking about Shenzhen! I think it was in the building I marked on the map, on the second floor. Let me know if you do find yourself out here, we can have an eevblog meetup

Thanks. That's an interesting map (screenshot), can you give me the source link? (It's not google maps.)
I don't yet know when it will be. There's some urgency, but I don't yet have enough money for the trip. May be some while yet.
When I know, I'll let you know. It would be good to meet someone there who knows the city.

Plus, anyone who knows the location of 2nd hand electronics stores, is my kind of guy/gal. 

[rsee]

Gray market buys are risky and more conservative sectors (industrial/hirel) steer clear especially if a certificate of conformance can't be provided.  The illegitimate business model makes sense.  Make a fake of an expensive looking part that is hard to come by.  Put a nice little markup on it because supply and demand will allow it.  Once money is exchange, worst case, they can disappear into the night.

Sounds like some people here have gotten lucky and the risk taken was worth it.  Hopefully you do too.

[janekm]

Yes indeed I was talking about Shenzhen! I think it was in the building I marked on the map, on the second floor. Let me know if you do find yourself out here, we can have an eevblog meetup

Thanks. That's an interesting map (screenshot), can you give me the source link? (It's not google maps.)
I don't yet know when it will be. There's some urgency, but I don't yet have enough money for the trip. May be some while yet.
When I know, I'll let you know. It would be good to meet someone there who knows the city.

Plus, anyone who knows the location of 2nd hand electronics stores, is my kind of guy/gal. 

Indeed, that map is from Apple Maps... Apple have licensed official Chinese maps so they tend to have the best English-language (up to a point) maps for China. Also full transit information now which is very handy! On Android one has to learn to recognise a few basic Chinese characters to get about using the Chinese apps like Baidu Maps

We could have a mini EEVBlog meet up in Shenzhen

[TerraHertz]

The two chips I ordered arrived. Well, they are 20 pin CERDIP, and have the right part number, but the date code is 1409, which seems very unlikely for a part that should have been made in the 1980s. Also the pins look far too shiny-new to be that vintage.

So rather than plug a 'could be anything' chip into my HP 54120 power supply, I breadboarded a very basic test circuit, enough to hopefully test the main zener supply regulation for the IC. Powered it up slowly, annnnnnnd.... nope. It was not doing anything sensible. Hmm... maybe the IC doesn't start at all unless the 'bulk supply' under-over check is OK? So I did a more elaborate breadboard circuit, pretty much identical to the actual power supply schematic around the IC.

Still nope... and the behavior makes no sense at all. Like it's some random piece of silicon that is just leaking a bit of current between pins.

But it wasn't doing anything that seemed like it would be harmful to the power supply. So I opened the 54120, pulled out the main power supply and removed the 1826-1120 IC. Tried that in my breadboard - it behaves a lot better, but still doesn't run properly. Oh well, nice try without any chip data. Tried the untouched new chip in the power supply, cautiously winding up mains with a variac. Nada. It doesn't even let the zener-regulated "14V" rail get above a couple of volts. Same as the other new one behaved on the breadboard.

(And then I put the original IC back in, and it still worked, to my great relief.)

OK then, so what are these chip-like things from China?
One nice feature of CERDIP packages, is you can pop the lid off cleanly, if you do it right. Which involves making a cleaver - a jig to apply a lot of shear force, while holding the chip to prevent it fracturing in other directions.
That only took a few minutes, and the chip popped open nicely.

I still don't have a good camera setup for my microscope, but do have a crummy adapter for my Canon EOS. Hence the poor quality pic of the chip.  But you can see it's clearly something digital, with an array - possibly a memory? The logo is National Semiconductor I think, and there's a number - DM3404. Google doesn't recognize that.

Anyway, they are fake. Some other part labeled with the number I wanted.

I wonder if claiming the money back via paypal will work?

Still to decide if I'll try again, with one of the higher price quotes.

[rob77]

thanks for sharing your experience  i hope they will refund.

btw.. looks like some kind of SRAM chip maybe ?

[daqq]

Looks like a memory. Certainly a logical IC. Thanks for sharing, sorry you didn't luck out.

[chris_11]

Yes that looks like an old memory. Nothing which could even remotely be used in a power supply.

BR
Christian

[SeanB]

Think I remember those, old fusible link ROM memory units. Obsolete in 1970 already, 8 bit by 256 or 512 bits IIRC.  The stuff i worked on used a few of them as combinational logic, getting a few dozen TTL chips into a single package. Another was a display decoder, driving seven segment displays from a digital input.

[bktemp]

It is most likely a PAL16R4. There is the national semiconductor logo visible and the text 16R4.

[dadler]

Contact the seller--OR just file a claim directly with PayPal for counterfeit merchandise.

[Richard Crowley]

Do we think this is a full-custom (BrEnglish: bespoke) chip?
Or is this just one of their standard products with  HP's house-number on it?
Or a special spec/test version of a standard part?
Is it not possible to correlate the package and pin descriptions against their standard products?