REPAIR AND RESTORATION OF THE SR-400
5
WDØGOF 6/22/20014
1. SR-400 INITIAL INSPECTION AND TESTING.
SO YOU JUST GOT AN SR-400 FROM E-BAY OR SOMEONE THAT
SAID “IT WORKED FINE THE LAST TIME I TURNED IT ON”. NOW
WHERE DO YOU START? THE FOLLOWING PROCESS HAS
EVOLVED OVER YEARS OF REFURBISHING THE SR-400. IT
SHOULD BE FOLLOWED IN THE ORDER IT IS WRITTEN. THIS
PROCEDURE IS DESIGNED TO PROGRESS IN AN ORDERLY
MANNER TO MINIMIZE RUNNING IN CIRCLES. YOU
MUST
HAVE
THE MINIMUM OF TEST EQUIPMENT LISTED TO PROPERLY
REHAB OR REPAIR THIS EQUIPMENT. BE AWARE THIS IS NOT
SOMETHING THAT WILL BE ACCOMPLISHED WITH GREAT SPEED.
THE AVERAGE TIME TO COMPLETION IS AROUND 60 HOURS.
SOME HAVE TAKEN AS MUCH AS 200 HOURS, SOME AS FEW AS 20
HOURS.
1-1. VISUAL AND MECHANICAL INSPECTION
Complete chassis cleaning and mechanical inspection are always advised. Cleaning of the controls, rotary
switches and the relays is of particular importance. Look closely for broken or burned components. Check the
rotation of the controls and mechanical stops of the main tuning dial (Section 8-8-A in the manual). Try to
eliminate the mechanical problem first. If you are going to upgrade to a higher production run complete those
upgrades before you start the electrical tests.
1-2. RECAPPING;
There are only six capacitors that are considered
must replace
components. They are: C70 and C218, 5 uf/25v;
C46, 25 uf/25v; C147, 2 X 30 uf/350v; C240, 175 uf/25v and C244, 500 uf/6v. C240 and C244 are found only
in the SR-400A. Capacitor C147 carries a heavy current load. Therefore the ESR rating of its replacement is
important. They should have an ESR rating of 1.0 ohm or less. ESR’s less than 0.3 ohm are available. This is
not a place to save money. C147 is a dual cap. There are sources for this capacitor,
but
be careful. Some
manufactures of these parts use inexpensive low quality parts. Don't buy from suppliers who will not quote or
guarantee the ESR rating. Very low ESR individual capacitors are readily available. So replacing the dual cap
with two capacitors under the chassis is sometimes a better solution. Generally speaking shotgun replacement of
the paper caps is not recommended at this stage of refurbishment.
1-3. AFTER MARKET MODIFICATIONS
If you find any modifications, re-wirings or added components remove them and return the rig to the original
configuration. For valid circuit modifications see k9axn in section 5-3.
