2445a power supply repair


Max Vlasov
 

Hello,

I've got a 2445a, which was burned by the previous owner (he was debugging the mains power supply without an isolation transformer). After repairs, where I've changed the channel #1 hybrid, TL072, TL074 and MC1458, now it seems, that the scope can be calibrated.
Before starting the calibration, I've checked the voltages on the power supply connector. All are nominal for exception of the analog +5 and -5 volts, which read well before the minimum.
I've got 4.78 and -4.76 volts. Voltages don't drift. Ripple is within the spec. The scope traces are stable before and after the warmup.
I looked at the PSU schematics and +5VA/-5VA are sourced via the linear regulators from the rectifier/filter. Could it be that the C1115 and C1114 caps have "dried out"? I don't see any leaks. Checked the capacitance, seems ok. Don't have a possibility to check the ESR.
Can I substitute a different capacitors instead of 250uFx20V?
Can I use for example, 330uFx25V?
Do I have to use the "low ESR" caps, or I can buy the standard "heavy duty" caps?

Than you!

Join TekScopes@groups.io to automatically receive all group messages.