Measurements taken with diode oriented as on board:
D228:
574mV from middle (-) to top (+)
576mV from middle (-) to bottom (+)
open from top to bottom (either polarity)
open with (+) on center lead to (-) on top or bottom
D229:
561mV from middle (+) to top (-)
574mV from middle (+) to bottom (-)
open from top to bottom (either polarity)
open with (-) on center to (+) on top or bottom
Should I begin testing Q210, Q212, Q214, Q245, and D222?
First, keep in mind that I do not have an RT-909 open before me. So your responses should be appropriately descriptive. In fact I haven't had one open before me for over 2 years.
Next, for semiconductor measurements, the polarity of the measurement should be explicitly stated (i.e., red or + to pin x, black or - to pin y, etc.) You don't need to specify color AND polarity, one or the other is sufficient, but I do need an indication of polarity in your recorded measurements. In diode test mode, meters supply positive polarity via the red lead and negative polarity via the black one. Please go back and edit you previous response post with that additional information.
Here is what a measurement should look like: 574mV from middle (+) to top (-)
Please note that a semiconductor can pass a diode test, yet still be bad. The power-on tests will give us additional information on the functionality of the components in view. That semiconductor tester I recommended would go significantly farther in detecting bad parts. We can make do for now.
I am sufficiently convinced that the rectifiers, D228 and D229 are not shorted. I do want to see the polarity update to your previous post (I will then update the above quote of your post). It is critical that those parts go back in, in the proper locations, because they are not the same part, one is inverted from the other. The S3VC10R goes into the D229 spot. In future, in case you are not already doing it this way, remove, test, and reinstall one part at a time.
Here are the parts to remove and test, as you stated, plus two more: Q210, D222, Q212, Q245, Q214, D223, ZD201. If any other parts have been removed/changed in this area, please list in detail which ones they are/were. Inspect the areas for shorts, circuit damage, broken wires, damaged components and report those as well.
Report back the out-of-circuit component test measurements and we will do the in-circuit functional test steps in a future iteration (do not apply power until instructed to from here). Measure and report between each pair of component leads (+ to -, then - to +). Don't be overly concerned if you see a single diode drop from collector to emitter, in one direction, with Q214. That part has a protection diode, across those 2 points, that is not shown on the displayed schematic symbol. It should show an "open" in the other direction.
I have a bit of concern, regarding ZD201. That is, I think I remember, that you had that part installed in the D223 position. I do not know, off hand, if it was designed for the forward current it would have seen in that position. The diode test will tell us part of what we want to know, then the brief power on tests, later, will tell us the rest, about that component. If it, instead, was the D223 part installed in the ZD201 position, you would have had excessive voltage on the output of the regulator, which would likely have overheated and damaged or destroyed the circuitry on the capstan motor board (D21, then IC21). Then, the transistors in the H-bridge could have been damaged or taken out. That could explain why you had heat and smell but the unit worked for a while before dying again. We will look at those components and circuit functions later.
The same excessive regulator voltage would have been produced if the unit had been powered up without ZD201 in place. Excessive conditions can be tolerated only very briefly, if at all. Hence, the manner in which we will conduct the next few tests (hang the leads for measuring a node, power up, take the reading and immediately power back down, terminating further testing upon detection of failure, until that failure has been corrected or localized.
Please note that this thread will be preserved and available for others with similar problems in the future. You are helping more that your own machine here. That is the value of a thread like this.
Enjoy,
Rich P
. In any case, you are welcome.
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