I bought a PB-503 that had been used in an electronics teaching school. The school may have altered the pin placement/connections to fit their in-house power, in the 4 wire round power supply plug that powered up my PB-503?? Internally, the bread board has three 7805 and one 7905, which tells me that the voltage regulators put out 0-5 VDV positive, and 5 VDC negative. The knobs are imprinted for putting out 5 VDC, 0-15 VDC positive, and 5 VDC negative. After adaping stuff to make my power supply, I exploded the negative 3300 mf capacitor two different times so far. Obvious I don't know what I am doing. The new owners of the Global Supply name, supplied me with their only documentation for the PB-503, but it must be for a much newer than my unit, as their manual had an internal power s
upply, where as mine has a round, four wire plug in socket, to supply power.to the bread board unit. New factory power supplies are not available, nor does it seem OEM schematics are available. My two questions: How are they getting 0-15 volts out of these regulators that end with 05 (five volt?), and does anyone have a schematic/wiring diagram for these really old PB-503 bread boards.
