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Signature Analyzer

Signature Analyzer’s Process

Convert the lengthy serial data stream of a micro-processor based product, into a four space alphanumeric signature

Signature Analyzer’s Purpose

This device can function as a troubleshooter for microprocessor-based products. Each node produces a documented signature during a specific mode of operation (free runnin'). Matching codes are contained in the product service manual. The signature analyzer reads the node’s code and visually displays it. A miss-match points to a fault.

An Example of a Fault

The signature table states that the code at A2 should read HHCO ( to be found in the service manual) If the Signature Analyzer’s display does not match the service manual’s code with the probe on A2, a fault exists.

Conclusion

The signature analyzer is a most useful fault locator, as the operation is fast and a problem area can be determined with some basic troubleshooting concepts. This device incorporates a minimum amount of hardware alteration and no software changes at all.

Lab Area

( You'll need the 8085 for this one along with the manual )

Setting-up the Free Run Mode

Set all of the data bus switches up, to enact an open loop.

Set the free run switch up.

Connect the four leads of the Signature Analyzer in this fashion. GND to ground, START & STOP to A-15 (by the address bus LED's), CLOCK to READ ( also by the address bus LED's) {pictured in the powerpoint presentation}.

Set the Signature Analyzer’s START, STOP, and CLOCK push-buttons out (rising edge).

Verifying the Free Run Mode

Take-up the probe (LED flashing on end) and put the metal point to the pins of IC’s 1 and 2. Compare the display of the Signature Analyzer to the code located in Appendix C-1 of the microprocessors’ manual. Any point may be cross-referenced in this manner.

Try This Out

Turn the microprocessor’s power switch off and then on again. The signatures of the data bus test points changed on account of new data now stored in the RAM. Hold the probe on the same data bus line and slide the corresponding input port switch (fiddle around to find the one). View the change of signature according to the switch position.

Setting-up the SA Test Loop

Set all of the data bus switches down to enact the Test Loop. Set the FR and SA switches down to put an end to the free run mode of the microprocessor. Connect the four leads of the Signature Analyzer to the pictured areas, add, the clock to the WRITE port. Set the Signature Analyzer’s START, STOP, and CLOCK push-buttons out (rising edge). Hit reset twice and now, move SA switch up then down.

Verify the SA Test Mode

Take-up the probe (LED flashing on end) and put the metal point to the pins of IC’s 1 and 2. Compare the display of the Signature Analyzer to the code located in Appendix C- 4 of the microprocessors’ manual. Any point may be cross-referenced in this manner.

Finding a Simple Fault

Remove W-10 from the center of the micro- processor’s board (one of the black plastic bits with a wire across it). Change the test set-up to match the information in table C-3 of the microprocessor’s manual.(all those switches we fiddled with to set-up the free-run and SA test loop). Give LED 4 the probe.(just below address display). A bad signature here points towards a problem from the IC doing the sending. Trace the signal back to output pin 12, IC 15. You will find a bad signature on this chip as well. De-solder and replace with like unit.

Continued Hunting

Probe the D4 input to the output port (IC15- pin13)and note the bad signature. Take the probe to the bus buffer output (IC15-13) for a good signature. It’s down to one PC trace. Probe the signal along the trace from IC15-13 heading to IC14-11, that’s the one. Put the jumper (W10) back…please

click here for a power point version of the background information

click this one for the power point version of the labs

press here for the sweetahh...... questions