IC7800 no RF output

Under constructions. 

This preliminary page is for reference only.

The power supply has been modified by previous technician. Possibly a faulty 8V and three 7808 are used to fix it.

Before dismantling rear panel

Cables in the rear panel

Rear panel removed

Screws for rear panel

The rear panel

Side panel before being removed

Cables on to the front panel

The final transistor has been desoldered by previous technician.

RF PA Unit

Condition during checking

Some burnt in the PCB

Side screw

Location of Silver screw

Screw on the side

Remove the screw as shown to takeout the tuner unit

This to remove PA

How ribbon cables are placed

From different angle

Remove speaker cable

After PA has been removed from the TXCVR

PA uncover

Replacement of PA transistors

It has seal and vacuum

Original bias setting, will be adjusted later

The other side of bias

So, after receiving the replacement transistors from Aliexpress. The repair went smooth.

To adjust the idling current, I choose not to connect the module to the radio. But instead, perform a stand alone test. This easier, since you do not have to place the module back and reconnect cables needed.

The trick is to put into transmit mode, that is, the bias is turned on and the transistor idling current can be adjusted.

Q1 is bias switch. It is turned on when transmitting. We are going to make it on without having the PA module connected to the Radio by grounding the base of transistor. Look in the board layout and choose where you can put a small wire jumper (soldered) for this purpose.

After adjusting the idling current, I put back all and tested the radio.

It works great .. 200W !