So I've got an old Clone Theory, and it sort-of works, at least until the BBD chip warms up. Yeah, it gets quite warm to the touch within about 15 seconds of applying power. When the chip is cold, it passes signal. When it's warm, it only passes "clicks" which I presume are clock glitches -- they are in phase with the 4047's signals.
With or without the BBD chip installed, the clocks look nice, good squarewaves from 0V to the 4047's VCC, which is around 13.5 V.
DC bias at BBD inputs (both stages) is about 4.5 V. The BBD's Vdd is about 12.3 V.
The BBD's Idd is about 65 mA, whether warm or cold.
Just for giggles, I put a 22 nF capacitor in parallel with the 4047's timing cap, thus slowing the clock down to 1.5 kHz, to see if the BBD wouldn't heat up so much.....nope, no perceptible effect. (Rationale: if something ugly in the clock transitions was causing the heating, then fewer transitions = less warmth.)
Is my BBD pooched?
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I just had one of these on the bench recently, but it didn't have the same problem. Just off the top of my head, have you checked all the caps connected to the BBD? Where is the gain trim pot (pins 11 and 12) set? Does the whole chip get hot at once, or can you tell if the heating begins on a certain part of the chip? Do any of the other chips get warm?
The schematic I have has someone's notes on it. So, (FWIW), one of the notes points to the middle lug of the balance trim pot and says "5VDC typ.". It's something else you can check, anyway.
> BBD's Idd is about 65 mA
That sounds odd.
The datasheet doesn't even mention power use, and 65mA should be worth mentioning.
The output section may pass 7mA.
The BBD sections.... the idle (no clock) drain should be nanoAmps or less. Clock chunks charge from device to device. Looks to me like most of this goes in/out the clock ports, and a lot of it cancels.
65 mA is way too much and suggests current is leaking through the BBD to "somewhere". Isolate inputs and outputs and see if the current drops. Then determine which component causes the large current to come in existence.
Quote from: Dirk_Hendrik on May 17, 2013, 10:04:11 AM
65 mA is way too much and suggests current is leaking through the BBD to "somewhere". Isolate inputs and outputs and see if the current drops. Then determine which component causes the large current to come in existence.
Rather belatedly, getting back to this.
Unfortunately, it would seem that the IC is what's dead.
Through the magic of IC sockets, I've connected all inputs to GND and the 4 outputs to VDD, as recommended in the datasheet. Still seeing the same current draw.....so, SAD-1024A is definitely very SAD (as am I). :'(
Thanks for all the suggestions, everyone. :)