Trying to identify an 18-pin chip...

On Thu, 18 Dec 2008 10:30:52 -0600, "Dave" put finger to keyboard and composed:

Does your Doorbell-Phone intercom have an FCC ID?

Is there a US patent number?

If none of the above, then you will probably need to reverse engineer the circuit. Otherwise you could try looking for similar devices at RadioShack:

The support documents may include parts lists, owner's manuals, and exploded views. Notice that most Catalogue numbers begin with "43".

Now go to the FCC site (see above) and search for the relevant RadioShack device.

RadioShack's Grantee Code is AAO (oh, not zero).

Type "43" or "63" in the "Product Code" box.

Type "200" in the "Show nnn Records at a Time" box.

The search results will include FCC IDs such as "43-nnnn" or "4300nnn" or "430nnnn". Be aware that RadioShack's numbering system sometimes converts a catalogue number such as "43-nnn" to "4300nnn".

The search results will often include circuit diagrams, block diagrams, technical descriptions, internal and external photos, user manuals, etc. Note that devices registered before the late 1990s may not have any lodged documents.

- Franc Zabkar

I think that it is highly unlikely that the IC would be a PLL in an intercom circuit. What is it about it that led you to this dubious conclusion ? Have you tried wiping a light film of oil across the top of the chip, and then looking very carefully under a strong light and magnifying glass ? Often, if they haven't gone mad with the grinder on the top of the chip, the lettering can still be read after this 'treatment'.

Arfa

Wow. FCC ID. Patent number. Of course. Shaking my head. Why didn't I think of these things?

And similar devices at Radioshack. Damn! Thank you, so much! I now have a whole slew of new possibilities to track down. Very much appreciated.

Dave

Hey Arfa,

Bottom line, it's a piece of communications equipment interfacing several different protocols, and a PLL is just what came to mind when asking myself "What could this chip be?" It appears to be at the heart of the circuit, and seems to be the center of activity. Do you have any other ideas as to what this 18-pin DIP IC might be? I am seriously asking here, as I am flying by the seat of my pants.

BTW, the top 1 or 2 thousandths of an inch of the DIP IC were literrally planed off, and there does not appear to be any remnents of it's identifying marks. I'll try the light coat of oil idea along with a bright light and magnifying glass, but recent attempts with something similar turned up a completely smooth surface.

Thanks,

Dave

Hello again,

I'm not sure what you are asking, here. What is "mains bourne carrier"? Is that a manufacturer? I thought it might be a PLL because of the application it is used in, which is a piece of communications equipment interfacing several protocols (it links in with the other controlls he activates by voice command from his bed or wheelchair. A very complex setup.)

Dave

The markings are ground off to prevent someone from directly stealing a design, or from stealing reels of parts and reselling them.

PLLs are common in any multi channel communications device these days. They are a lot cheaper than a handful of separate crystals, and only one or two oscillators have to be tweaked during final testing.

Over the power line, AKA as 'Carrier Current'.

Don't think you mean PLL - "phase locked loop" somehow. What do you think PLL is an acronym of?

Perhaps your previous experience of ripping radio equipment apart has been to stop at the spider thing and call it a "PLL", as the radio jobbie is lacking several crystals so that's what it must be (among other things) - but there are many things with multiple legs doing multiple things in most bits of kit now.

The chip is probably an ASIC "application specific integrated circuit" or possibly some variant of microcontroller.

Um, I am indeed thinking "Phase Locked Loop."

I was thinking that they used a more or less commonly availale part and planed the numbers off to frustrate people like me, trying to fix the stupid thing. They don't offer service/repair, only sales of new units.

Thanks,

Dave

Like the others, I'm still struggling to associate a PLL with the application. The chip could be almost anything from an ASIC as Adrian suggests, through microcontrollers like PICs and similar, to an audio preamp or even a logic IC. PLLs are used typically where a frequency needs to be kept stable by being locked to some other frequency source, or where a number of frequencies need to be generated with the change between them being quick and easy, or under uP control, such as in a multi-channel radio transceiver, or sometimes for the purposes of demodulating an FM signal.

The reason that you were asked if it is a mains-borne system, is that sometimes, household mains (U.S. line power) wiring is used to communicate between several units which are remotely located from one another. To do this, a high frequency carrier is generated. This is then modulated by the comms data, and then injected into the household power wiring by the master control unit. 'Slave' units are then plugged in at wherever they are needed, and these are able to pick off the HF carrier, demodulate the code stream, and determine if the data being sent is for them.

The HF carrier is quite likely to be generated using a PLL, and the code demodulator at the slave may well also use one.

As for your contention that a power resistor is being overdriven by the problem to the point that it is scorching the board, this is probably a red herring. Power resistors often scorch boards when operating completely within their specs, particularly if the board substrate is an SRBP type.

What was actually wrong with the cap which you replaced ? It is rare for electrolytic caps to 'blow' as a result of any external influence like storms. Is this board too complicated to rev-eng so that you can get a better idea of what the circuitry on it is ? If it's not too big / complicated, it's sometimes possible to use a flatbed scanner to take a picture of the print side, and then to draw in the components by hand as circuit symbols. It's then not especially difficult, if a little tedious, to derive a basic schematic. If you could take a photo of the board and post it somewhere, it might give us all a bit more of a clue about the support components around the chip, which may help to at least identify its basic function.

Arfa

On Fri, 19 Dec 2008 16:25:59 -0000, "Arfa Daily" put finger to keyboard and composed:

I've had a look at the parts lists for various Radioshack intercoms. Many of the "mains-borne" designs appear to use an LM567 and an MC14069. Some also have an LM386 amp to drive the speaker. The carrier frequency appears to be 200kHz. One could expect that these intercoms would require additional ICs which are not included in the parts lists. For example, there may be surface mounted types which cannot be supplied as spares. However, ISTR taking apart one of these intercoms a few years ago and I don't recall seeing anything particularly complicated. In fact the datasheet for the LM567/NE567 suggests that this IC can function as a "carrier-current remote control or intercom":

- Franc Zabkar

"Arfa Daily" wrote in message news:uWP2l.44200$ snipped-for-privacy@newsfe29.ams...

Hey again,

Hard to know where to start, but I suppose I should begin here by mentioning that this intercom unit interfaces with the microprocessor controlled device over his bed (called a Quartet) which gives him control over the opening of the door, the operation of his telephone (to answer or make calls) and a host of other tasks, all by voice operated control. It is more than a simple intercom, even if that's what I call it. Doorbell-Phone is the name of the company that manufactures/sells this device. I forget the model number. I will see if I can get a picure of the board to upload to A.B.S.E. As for the power resistor, it appears to be a five-watt or so, but seems to be dissipating something like 25 to 30 watts of power. The cap, if I recall correctly, appeared to have overheated. Originally thought it was probably shorted and that replacement would correct the failure. Replacement only put a new (also high-temp) cap in it's place. Also replaced the audio-amplifier transistor associated with that cap, and observed that the overheating resistor was still far, far too hot to touch. The two resistors next to that one, of similar type, were barely warm. Following the circuit back from the resistor/cap/transistor led me to the 18-pin IC in question. And I could easily be wrong about it being a PLL. I honestly forget now what led me to that conclusion, as it has been several weeks since I last worked on the device. I am hoping to get my scope down there and check the one pin for a clock pulse and the other for continuity with ground to see if it *could* be either of the two PLLs I have identified as possible replacements for that chip. If that doesn't pan out, I'm out of ideas. As you point out, it *could* be nearly anything.

Thanks,

Dave

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If zapped by electrical storm , why is most of the system still working? Please put any pics on a proper website,eg the the one I use below is quick and easy to set up, at no cost.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on