Began testing complete system, then self inflicted damage I must repair

ALL COMPONENTS INSTALLED AND TEMPORARY CABLING INSTALLED

Once I had all the parts installed in place and after the main board had checked out properly, it was time to connect the front panel/front board sandwich to everything else so that I could finish the testing. I have male plugs on order to build the various cables for a permanent interconnection but used a number of breadboarding style jumpers in the meantime to be able to start on the testing. 

BEGIN THE VERIFICATION AND CALIBRATION PROCESS

Early on in the testing I discovered that the -15V 'step' power supply was missing but +15V was good. As I was tracing down the issue I discovered that one of my temporary connections between the main and front boards was not wired properly. I had reversed the + and - step supply connections to the front board. 

When I fixed that issue, the +15V supply was now at zero while -15V looked fine. The fault is on the front board/front panel sandwich and I realized that I had blown out some semiconductors by reversing the power initially. 

I started a damage assessment to identify all the parts that might have been damaged by the reversed voltage, so that I can remove them, order replacements and put the new chips in place. If this were a traditional kind of board with a single set of power rails and I had reversed the connection, it could have fried every chip. Fortunately, the scope of the damage was limited. 

ISOLATED POWER SUPPLY LIMITED DAMAGE TO SPECIFIC CIRCUITS

As part of the design of the curve tracer, the step circuitry has its own power supply, with its own isolated ground, thus only the parts connected to the step supply would be impacted. The circuit is not trivial, but the problem was restricted to just this area. 

NINE IC AND TWO DIODE PACKAGES REMOVED AND REPLACEMENTS ORDERED

Nine integrated circuits, consisting of op amps, digital logic and a timer, were exposed to reverse power and had to be considered compromised. I ordered the parts from Digikey except for the timer chip which was out of stock. Mouser had the timer so I added an order with them. Fortunately, I had extra units of the two double-diode packages that were damaged so I didn't need to order them. Including shipping and tax, this was an error that cost me $35 and a week delay. 

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