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Old 6th January 2013, 08:57 PM   #1
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Default Old breadboard from a college program???

I have just acquired a older (circa 70's I think) "teaching aid... probably a teaching aid for an electronics course.

It's labeled as NIC and is a breadboard with built in signal generator and 12 +. 12-, 5+ VDC power supply and a breadboard. PCB is labeled North Idaho College 7-77.

I found it at a garage sale, homeowner said it was her husbands from college (now deceased). The bottom of the chassis is missing and a number of wires have been pulled lose and/or missing. I have the power supply working

Signal generator is using a LM3900N in it's circuitry, but a second IC is labeled only as a 7516 dual 8 pin IC It has the Exar logo on it, but I can find no information.

anybody have knowledge of the Exar 7516 - Their website gives the appearance that they're no longer in the chip biz.

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Old 7th January 2013, 03:04 AM   #2
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7516 is probably the date code, 16th week of 1975.

Exar was famous for one chip, the XR8038. It is a waveform generator and was made by a few other vendors. Intersil comes to mind. It is however a 14 pin chip. It could also be a NE555 variant.
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Old 7th January 2013, 03:12 AM   #3
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Exar had an 8 pin oscillator chip totally different than 555 but that does not seem to be the one. Possible is that it is XR4151, v to f converter.
If not available, u can use LM2907/LM2917

Gajanan Phadte
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Old 7th January 2013, 03:29 AM   #4
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Thank you much!!!!!
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Old 7th January 2013, 03:40 AM   #5
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Other chip no. is XR2206.

Gajanan Phadte
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Old 7th January 2013, 06:20 AM   #6
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Location: St Louis, Mo
It sounds like you have a unit that is variously described using terms like "benchtop trainer", "universal breadboard", "tabletop electronics lab", et al. They were - and continue to be - staples of the electronics education industry. Over the years there must have been hundreds of companies that produced them in various formats. Some of the correspondence schools, as well as a few traditional colleges and high schools, had somebody's standard model "customized" in some way (maybe just a silk-screened logo on the panel), and a few even crafted their own versions in-house. In my opinion it's worthwhile to have one of these things on the bench.

If you can identify the original manufacturer, you may be able to locate a schematic and parts list. (For example, you can get the schematic for one variant, the "PAD-234A", at http://www.elexp.com/tst_234.htm ) While the basic architecture of these units was quite similar from one manufacturer to another, the implementation details varied quite a bit. In a school environment they took quite a bit of abuse - and, frankly, many of them didn't have adequate protection circuitry or suitably over-rated components to hold their own against students' mistakes. If all 3 power supplies as well as the function generator of your unit are working, you are fortunate!

I've looked at either hardware or schematics for at least half a dozen of these trainers, and all the "Function Generator" sections used the '8038, or some variant or descendant of that chip such as the '2206. It's mentioned in "25 Microchips That Shook The World" - but I know that it was available at least a decade earlier than the listed "1983" introduction date. At one time I think there were 3 or 4 different manufacturers of functionally similar chips but all of them have been discontinued. (Exar may still offer the VCO section of the '8038 as a stand-alone chip, but it doesn't have the waveshaping circuitry.) You may find the chips at some of the places that carry surplus/salvage components such as All Electronics, Jameco, Marlin Jones, etc.

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Old 7th January 2013, 01:35 PM   #7
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I'll look at the 2206

I looked at the schematic for the PAD-234A and it's considerably more sophisticated than the unit I have, though it appears to have the same analog 'controls' . I'll get a photo of the unit tonight, if for no other reason it can be thrown in the "Way Back" machine

It looks like there was a modification to it- pin 10 and 11 of the EXAR chip are pulled and the emitter and base of an NPN diver (MPSA06) is plugged in and then stick into spot on the board that doesn't appear to be part of the original design. I need to trace out IC
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Old 7th January 2013, 08:13 PM   #8
Enzo is offline Enzo  United States
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Anything like this old beast?

Click the image to open in full size.
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Old 7th January 2013, 08:42 PM   #9
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not even close--- yours has meters and what looks like a built in speaker

and considerably larger
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