How long can equipment go unused before powering up runs the risk of damage?
Risk of damage is low, risk of poor operation from cap seal failure is high after 20 yrs, depending on many factors. ( See end)
This was an excellent transceiver. But it is so old that the service manual used MF for uF=μF and yet UH for uH=μH.
MF is these days means millifarads, not microfarads as in this unit service manual.
The 100W Tx will have need of good low ESR e-caps on supply for low ripple if they need replacing.
Do not operate Tx without a dummy load or antenna.
- Get the service manual below. or email to them for service related questions.
Get a DMM to measure Vdc and Vac ripple on large caps where the ripple voltage must be << 1% of Vdc to be considered good. ( Dissipation Factor, DF at 120Hz in datasheets.)
Unfortunately the service manual omitted the power supply board which is the main concern for worn out e-caps after 10 to 20 yrs with low C and high ESR values.
- so you **want to wing it* by looking for signs of slight end-bulge and measurements or hum on Rx or Tx.
- If everything looks OK, power it up. The only potential damage can be from pressing Tx without a load.
a portable RLC meter is often a good investment to verify caps out of the circuit.
anecdotal: When my Sanyo receiver was 15 yrs old and had spurious noise, I found one bad electrolytic or e-cap then replaced all of the similar size or bigger and discover a few more were also bad. so I ordered/replaced about a dozen of them. The cost of parts are cheap from Digikey and often less than the courier cost.
At one-time Computer grade, 100k uF capacitors had high leakage currents which could be conditioned by a high series R to clear up the leakage currents. This, unfortunately, does nothing from failed caps that suffer from high Effective Series Resistance (ESR) and low Capacitance. As others have said. it won't help.
Like Batteries, also have wet electrolyte the age or MTBF is very much reputation of the brand used and it's high-temperature rating and the ratio of ripple current and voltage to the rated maximum.
E-caps are rated by hours of life at 85'C or 105'C or others since the accelerated life of 1500 hrs is all that caps can endure due to Arhennius Law. So not only is possible to generalize lifetime but suffice it to say, room temp seal quality, brand name and high temp rating, historical operating stress makes it impossible to predict. All I can say is even the best caps made in Japan will fail at some point, whether it is 5 yrs, 10 yrs or 50 yrs it is impossible to guess.