Question Amp - Quiet left speaker issue

[LaFayette1777]

The left speaker is more quiet and the sound crashes. It can improve (but not always) after 5 -10 min. More often I have to slap the top of the amp (Marantz PM7200 I bought 18yrs ago) to get the sound back to normal. The issue persists after bringing this amp twice to a local repair music instrument shop.
1/ Any idea what the issue is with the amp? (I tested speakers, cables and the issue comes from the amp)
2/ Could turning-off the amp directly damage amp parts/components? (instead of putting on stand-by with the remote control before turning off the amp)
Thank you for your views.
3/ Do you recommend a shop to fix this in London?

 

[bandit pilot]

If it works at all, it could be down to a dirty volume or selector switch (or any other switch). failing that, possibly a dry joint.

 

[Lawrence001]

Capacitors can often be a cause of noise, slapping the top might make them work better if they're dried up (as they can rattle about?

I had an amp like that where tapping the top of a cap made a noise through the speakers that's a way of telling.

 

[toprepairman]

Most likely a dry joint.

 

[Strider]

The left speaker is more quiet and the sound crashes. It can improve (but not always) after 5 -10 min. More often I have to slap the top of the amp (Marantz PM7200 I bought 18yrs ago) to get the sound back to normal. The issue persists after bringing this amp twice to a local repair music instrument shop.
1/ Any idea what the issue is with the amp? (I tested speakers, cables and the issue comes from the amp)
2/ Could turning-off the amp directly damage amp parts/components? (instead of putting on stand-by with the remote control before turning off the amp)
Thank you for your views.
3/ Do you recommend a shop to fix this in London?

It sounds like a dry joint somewhere between a component and the PCB, finding where the issue lies is bit if a pain to be honest and will probably cost more to fix than replace. It could damage one of your speakers if your 'slap the top' if a component shorts out!
Turning the amplifier off as opposed to standby won't damage anything, leaving it in standby might help reducing the dropout because the residual current should keep the components warm and bridge the dry joint.
Have a look on eBay, they were a good amp back in their day so tend to keep their value.

 

[robbyrtp]

Class A amp getting hot and cold has probably taken its toll after 18 years.