Technics ST-CH7L (CH-7 system). Won't come out of standby.

There I was, minding my own business having a walk at lunchtime along the side of the Avon river, and I bump into a guy I haven't seen for the best part of 15 years. Mark the aerial guy, which is very helpful as I need some aerials fitted on the top of the workshop. Excellent timing.

A couple of weeks later, Mark arrives and sort the new aerials as arranged. He does a superb job as always.

"I've got this Technics hi-fi which won't stay on... could you have a look for me?"

Yeah .... why not?

It's a CH-7 system. Sort of faux-separates where each unit is connected by a ribbon cable to the main amplifier unit. This one refuses to come out of standby. Press the power button, it comes on and instantly off again... 

Eventually it does come on, but the tuner is displaying rubbish... 

A couple more power cycles and it settles down, and works correctly.

You may also notice the display on the amp is all foggy..

The tuner contains all the control circuitry, so I'm going to focus on that first. 

Five screws (two on each side, one on the back) allow the top to be removed. We also need to get the front panel off, held on by two screws underneath.

The screws are removed that secure the PCB to the base... 

The more observant of you will notice the transformer.... surely technics didn't put a mains supply on the ribbon cable? Panic not. This transformer has a 24V primary!

...and the back panel removed to we can remove the main PCB...

R704 looks to have had a hard life. It checks out ok though...

... unlike some of the soldering on the board, which has started to crack up, it's re-worked.

The thing is temporarily reassembled to see if the poor solder is the cause of our issue...

Hopes of a quick and easy fix now fade, it's still the same.

A quick look at the diagram shows there are two main rails, 14.8V , regulated by Q703, and 6.2V , regulated by Q701. 

The 14.8 volts reads good, but not so the 6.2V... it's low at around 4V during the fault condition, but rises up after we have a few goes at getting the thing out of standby.  R701 & 703 check out ok, C704 looks ok on initial inspection, but when removed for testing smells very nasty ! It's job is to stabilise the base voltage on our pass transistor. It's electrically and physically leaky.. C702 measured a little high on ESR, so it's swapped out...

Bingo, the unit is now functioning reliably.

Now to sort out the foggy display on the amp.. 

The top cover is removed, and the front panel in the same manner as the other unit. 

The visible screws are removed from the rear of the front panel PCB. The front panel is made up from two PCB's, we only need to remove the top one.

Pull off the knobs, and remove the 12mm back nuts on both controls.

The pcb is pushed out from the front by pushing on the control shafts. It's got a sort of haze over the vacuum florescent display...

... and the filter in front of it...

... which is easily removed with a spot of window cleaner and a microfibre cloth... 

... and once reassembled, a nice bright display is restored :)

Another saved from landfill !

The guilty parties...