Taiyo direction finder, troubleshooting

[Hoogin]

Hello, i have a Taiyo direction finder which is malfunctioning. I've narrowed the problem down to the power supply with the help of the schematics found in the instruction manual. I have trouble figuring out which components which are at fault.

Symptoms
When you turn on the unit it takes a little while can be directly or a few minutes the lights and display starts blinking. Your hear beeps in the speaker and bangs. It's unusable.

Measurements
I measured the 5 volt and 9 volt lines with oscilloscope and the 9 volt line is jumping from 9 volts to around 8.8 volts and back, at the same time as it does that the 5 volt does the same but from 5 volts down to 4.5 volts.

I've attached the parts of the schematics which involves the power supply.

I'm thinking there might be a busted cap somewhere?

Since I'm fairly new to electronics any insight or help is really appreciated.

[ElektroQuark]

A very good and detailed set of images of both sides of the power supply PCB assembly are a must to be able help you.

[Hoogin]

These are the best pictures i could take with my camera. Can borrow a better one this weekend.

[Rufus]

I measured the 5 volt and 9 volt lines with oscilloscope and the 9 volt line is jumping from 9 volts to around 8.8 volts and back, at the same time as it does that the 5 volt does the same but from 5 volts down to 4.5 volts.

'jumping' doesn't tell us anything much, post a trace or photo from the scope?

My guess is an intermittent overload on the +5v supply which puts the 5v regulator into current limit and the 9v supply feeding the +5v regulator droops a bit with the overload.

[Zad]

When the fault shows, tap the board with the insulated end of a screwdriver. If the voltage fluctuates then you have a dry joint and need to examine the relevant solder connections with a magnifying glass.

If the voltage regulator is getting hot, then suspect an overload or short circuit somewhere.

Check all the related electrolytic capacitors for any sign of bulges or deformation of the casing. Electrolytic capacitors are one of the least reliable components, especially cheap ones.

[Hoogin]

When the fault shows, tap the board with the insulated end of a screwdriver. If the voltage fluctuates then you have a dry joint and need to examine the relevant solder connections with a magnifying glass.

I tapped it when it was acting up and it stopped. I tapped it again and i saw on the oscilloscope that the 5v line fluctuated but the 9 volt did not.

This afternoon I'm going to be able to take better pictures of the board. I'll look around and see if i can find any odd looking joints or caps on the board.