When not to use an isolation transformer

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What would happen if you plug in the transformer first and powered up and then plug in the TV, then turn on the TV?"  The Tv sits there and usually blows the protective circuit breaker on a PR 57 or refuses to start. Sometimes cycling with an audible whine. Parts could be damaged. . Most of the sets had no power transformers and needed the isolation the PR57 provided. The sets were unable to get a high enough instant current surge to get the SMPS to start. Plugging directly into the line was the only way to get them to start. (Typically on some specific models of RCA sets IIRC). Some sets would blow parts if used on a lower than designed operating voltage also.  We seldom used dim bulb testing except on stereos or as loads. The shop only had the PR57 units, no high current variable transformers or high current isolation transformers.

What would happen if you plug in the transformer first and powered up and then plug in the TV, then turn on the TV?

Or connect the dim bulb on as a load before turning on the TV As a parallel load rather than series?

I have a General Radio Variac and can use an isolation in series, but having a bigger wattage rating on the Isolation transformer?

OK .
I have beat it into you to ALWAYS use an isolation transformer for servicing.

Well there is one major exception.

I worked on a lot of RCA color CRT type TV sets.

In using a Sencore PR57, (Isolation and variable output voltage transformer unit); many of the sets would not turn on after servicing.

The PR57 did not allow enough start up inrush current to allow the set to start up.

So out of necessity, I needed to plug them directly into the line.

This is the only exception I ever found, but it took me a while to figure out what was going on.

So I thought I couldn't be the only one with this problem and wanted to share the answer.

It IS a good idea to invest in a high current isolation transformer in a case like this.