Small teardown: an old TEK IC - Page 1
Forum section: electronics / general

author: muvideo
author_rank: Frequent Contributor
timestamp: July 25, 2012, 10:46:05 pm
content: Hello, this is a small teardown, I'm thinking to replicate an old tek icfrom discrete components, it's a 155-0013-00, a logic ic containingthe equivalent of one T flip-flop and few gates.I'm still figuring out the possible logic levels, someone on the TekScopesmentioned that probably these ic are RTL logic.I had one defective unit: it's working but doesnt follow correctlythe truth table, it's canned, so easy to open:here is the chipsome close up view, changing the lighting shows 2 series of parallel lines,at 90 degree. I dont know anything of IC technology, is it possibleto spot transistors and resistors, reverse engineer the schematic?Near the Pin 7 there is also an odd track that probably can be the damagedarea.This is the logic diagram of the chip:http://www.flickr.com/photos/14336723@N08/7635785700/#Fabio.

author: amyk
author_rank: Super Contributor
timestamp: July 26, 2012, 08:14:15 am
content: The metallic trace-like regions you're seeing are the metal layer. The faintly visible lines are probably polysilicon ("poly"), used either for general interconnects or as resistors. Some of the vias are also faintly visible. The poly layer will be under the metal layer. Adjusting the depth of field should make them more obvious, and you might be able to see the vias more clearly too. I'm not too familiar with bipolar stuff (used to CMOS, which can bevery clear to decipher the FETs) but looking at theconstruction of a BJTthe repeated structures I've outlined in the picture are probably transistors. The one near pin 7 does look damaged. I've also pointed out a few of the poly resistors. You'll need to get better die photographs and more info about the logic family used, pinout, etc. if you really want to recover the schematic. The visual6502.org site might have some samples of bipolar chips too in their image archives.

author: muvideo
author_rank: Frequent Contributor
timestamp: July 26, 2012, 09:37:56 am
content: Thank you amyk for the tips,I have some info from the service manuals, this is the blockdiagram of the IC:http://www.flickr.com/photos/14336723@N08/7635785700/#in that flickr albume there are some other images, one exampleof in curcuit usage is here U2530 U2535 U2540:http://www.flickr.com/photos/14336723@N08/7635785570/#I know that Pin 5 is Vcc +5Vpin 2 GNDpin 9 is connected to the can so to the bottom of IC, in circuit it is tied to -15V trough a resistorpin 6 is outother pins are inputs.Logic levels are not very clear from the schematic, some inputs aredirectly connected to 0-5V, some others are connected to lower levels,the output itself is annotates as 1V high level.Is there a rule for the relative position of E B C regions of thetransistors? Or I should deduce from the schematic where is theBase etc?As for the image, I'm limited by my setup, but I think the lighting canbe greatly improved, in that image the lighting was from ambient,and are visible vertical structures, if I light from another orientationI can see orizontal features. Any tip for improving the features visibility is welcome.Fabio.

author: muvideo
author_rank: Frequent Contributor
timestamp: July 26, 2012, 11:40:31 am
content: Another 3 images, I have a flare problem with the microscope.

author: free_electron
author_rank: Super Contributor
timestamp: July 26, 2012, 04:52:03 pm
content: Looks like the metal coming from the corner wire into the transistor is toast ....The 'line's you are seeing are the edges of underlying structures.This chip is single layer metal, Bipolar process.Here is a document that show how the transistors are built. You will recognize this shape immediately on the chiphttp://users.ece.gatech.edu/pallen/Academic/ECE_4430/Summer_2004/L160A-BJTTech(2-UP).pdf

author: muvideo
author_rank: Frequent Contributor
timestamp: July 26, 2012, 06:18:43 pm
content: Quote from: free_electron on July 26, 2012, 04:52:03 pmIn fact, observing visually trough the scope there is an area where the metallization is absent and thereare what seem small spheres, likely residue from a local fusion this would explain the behaviour of the chip.It's fascinating to observe by eyes the actual ic damage.Quote from: free_electron on July 26, 2012, 04:52:03 pmInteresting, so the two pads that are closer should be base and emitter, the other more spacedapart is the collector. Is there any hint of being npn or pnp? Seem that npn is simpler, is it possiblethat the chip is made only of npn parts?Fabio.

author: SeanB
author_rank: Super Contributor
timestamp: July 26, 2012, 06:45:16 pm
content: PNP will have a diffusion ring around it, and will be slightly larger. Most likely all NPN, as high gain lateral PNP transistors are difficult to make, and were actively designed around.

author: free_electron
author_rank: Super Contributor
timestamp: July 26, 2012, 07:36:40 pm
content: Yellow rectangles are transsitors.Red circle is where it went 'boom'Blue rectangles are resistors.There is , what looks to be , a mulit emitter transsitor , possibly a current bias generator of some kind on the left ( green rectangle )The dark blue structure is possibly a current reference. ( one transsitor with e/b shorted to act as diode steering another one )

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 26, 2012, 07:51:53 pm
content: although I agree that it is an interesting experiment it looks like you can buy the thing for $ 10,-http://www.qservice.tv/vpasp/shopexd.asp?id=10781http://www.ebay.com/itm/Tektronix-155-0013-00-155001300-Custom-IC-NEW-/140740075706

author: muvideo
author_rank: Frequent Contributor
timestamp: July 26, 2012, 08:10:39 pm
content: Quote from: PA0PBZ on July 26, 2012, 07:51:53 pmI know that this chip is an easy find, but the reverse is more funFabio.

author: amyk
author_rank: Super Contributor
timestamp: July 27, 2012, 08:46:07 am
content: Try lighting with different colours and viewing more obliquely. That might be able to bring out some more of the detail.

author: muvideo
author_rank: Frequent Contributor
timestamp: July 27, 2012, 01:14:03 pm
content: I will try to highlight better the edges, free_electron I was thinkingthat B-E should be the two closer contacts, and C the one slightly far,can you explain how you recognized the relative position?Thank you.

author: muvideo
author_rank: Frequent Contributor
timestamp: July 27, 2012, 03:45:27 pm
content: I took more images and applied a little of post process, now the edges area little better:

author: amyk
author_rank: Super Contributor
timestamp: July 29, 2012, 07:42:49 am
content: Great pictures. You can clearly see Q16's emitter connection is blown out and the residue that remains. It's RTL, all NPN. The -15V to the substrate is for reverse-biasing the parasitic diodes between it and each transistor (substrate is P, transistor's collectors are N wells, so there is a diode formed between them) to prevent them from conducting.Q20 may have been purposely configured backwards.I could derive the schematic and the gates from them. A quick simulation confirms that its operation matches the table in the manual. The actual gate-level schematic is a little different, 3 OR 4's output is used to reset the flip-flop too. I've labeled on the gate-level schematic the associated transistors for each gate, and the 4 flip-flop outputs with the resistor providing the pull-up on its node. The T flip-flop is the usual master-slave design.Have fun trying to build a replica from discretes

author: muvideo
author_rank: Frequent Contributor
timestamp: July 29, 2012, 08:23:16 am
content: Thank you amyk, great work!I made some better pics with tilted surface and different lighting:This is the image sligtly enhanched:This was my best bet, comparing with your reconstruction seemthat I nailed many of the features, but not all, and screwed b-e positionsFabio.

author: muvideo
author_rank: Frequent Contributor
timestamp: July 29, 2012, 09:03:46 am
content: amyk one thing I dont understand, yourself talked about blown Q16 (in your notation) emitter,this connection goes straight to pin 7, but in your schematic pin 7 goes to Q16 base.In my reconstruction Q16 base is connected to R20-R24 emitter to input and collectorto R20-Q15 base, is it possible?

author: amyk
author_rank: Super Contributor
timestamp: July 29, 2012, 09:35:51 am
content: I'd say it's not impossible, but in RTL inputs are usually connected to bases.Emitters as inputs are a characteristic of TTL.