I had no warning of failure, the 485 had been on foe an hour>and when I came back half an hour later the +13V line was dead.
>Now 13<15, but not by as large a margin as I would have liked.
>One tant was a short, one 86R6ohm (!) resistor was toasting itself,
>and fortunately the 741 has current-limited outputs :)
>Currently I'm using 10uF 15V replacements I had to hand, but
>they are relatively easy to replace should I feel the urge.
>(My s/n is 702507, but I can't date that)
I suppose you are aware that there is no "+13V" rail in the 485?
Unless there is another rail offsetting the 2V difference, U1910 (power supply regulator) should have kicked off the inverter when the +15V rail went 2V low.
After the short, was there an audible clicking from the inverter? U1910's balance node should be sensing the current from the short and stopping the inverter.
I've gotten into the habit of checking every dipped tantalum for shorts and excessively high ESR in each scope before bothering to do much troubleshooting. Is this 485 a scope you've had for a while and been using, or a project scope you recently started working on?
I don't know enough about Tek's SN info or manufacturing to date them by that - if it's possible. The way I date my scopes is by seeing what the most recurring, earliest date codes off of components are.