Yaesu FT-707 AVR Relay Replacement
In depth construction details are shown on the following pages complete with printable pcb artwork , parts lists and other info. This information is provided at no cost to Hams doing repairs on their own radios.
Perhaps the biggest source of trouble that occurs with the FT-707 is that of damaged relays. If this radio only had one or two relays , then it could be easily dealt with , but the 707 has nearly a dozen relays of various sizes and configurations.
As with any fault it pays to understand the cause of the failure , and then make a suitable repair that fixes the fault and addresses the cause so future problems are avoided.
One trouble spot in the FT-707 in particular is the relays on the AVR board.
The AVR board looks after the voltage regulation in the rig and some switching between RX and TX.
The main fault affects RL-01.
This relay is prone to sticking and burnt contacts.
Burnt contacts can be have various causes , including-
1. Over current.
2. Back EMF causing an arc at the contacts.
3. Incorrect relay type used.
Yaesu would have , or at least should have , measured the current consumption and chosen a relay with a suitable contact rating. However , the current rating of a switched contact is only applicable when a purely resistive load is being switched.
If the load (or the supply) is highly capacitive or inductive this can cause significant damage to the contacts as the current or voltage is far higher than expected , even though it may be just for a split second.
Some Hams have replaced RL-01 with one that can handle a higher current , but even this often doesn’t cure the problems and eventually the bigger relay dies before its rated life span is reached as in this case below.