HP-35 Power Supply Waveforms

[cruff]

(04-06-2019 09:22 PM)albertofenini Wrote:  That is a good indication,
how much should be the value of the resistors that simulate the load ?
Should be connected between the Voltage point and ground, right ?

Yes, between the voltage and ground. The resistors would be sized to sink a current similar to that of the individual loads. For example, I believe that Vgg is used as a substrate bias voltage for the ICs, so the current flow is probably below 1 mA. If I remember correctly Vcc is the LED drive voltage and Vss is the voltage for the remainder of the calculator. Has anyone taken measurements? Perhaps several hundred mA for Vcc and 50 mA for Vss (which might represent idle and no card reading)?

Quote:On the other hand, the guide that we use to repair the HP65 shows how to test PSU
off load, de-soldering cathode of CR2 and the anode of CR1

What does that guide say you should see for the voltages?

Quote:and de-soldering the cathode of CR4 and the cathode of CR5 from the logic board, lifting them up, and solder them together

That would eliminate a bad circuit board trace between CR4 and CR5 as a possible problem, and removes the load the digital circuits placed on the +6V output. What does that guide say you should see for voltage?

Quote:This means that good values should be available also off-load, right ?

That assumes the power supply has sufficient capacity to source the load at the regulated voltage. It might not, and thus may be designed for a higher no-load voltage and at the design current will drop to the required voltage.