My Dead SX-980

[matt gholson]

Started investigating the unit, its missing one knob, but otherwise seems pretty good on the outside. Insideobvious signs of meddling include new indicator bulbs that were spliced in and had electrical tape wrapped around the wires. Of course the most obvious thing I noticed was the main bulbs near the power supply were hot enough to melt and break their plastic tabs and were just hanging around.

I downloaded the service manual and started looking at the diagram of the power supply and pictures of them online. I had noticed a part that didn't really look like it belonged, a big resistor. Then I realized it wasn't really attached to the board very well underneath.

I pulled up the power supply board and looked underneath. I've got zero experience working with boards but it looks kind of rough under here.

 

[tsd71]

Nice receiver,that power supply in the 980 gets very hot right around the two heatsinks on the right side,you will HAVE to rebuild that power supply, as you can see from the second picture the solders are cooked. Also the diodes behind those heatsinks get fried too so they should be replaced too. Where are you located?
Here is a list from Mark for all components on the board.

q1 2sd712 100v 4a 30w 55-300hfe 8mhz
512-KSC2073TU npn to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54
q4 2sb682 100v 4a 30w 55-300hfe 8mhz
512-KSA940TU_Q pnp to-220 bce 150v 1.5a 25w 4mhz 40-140hfe $0.54
neither side is going to come close to an amp of current, no less 4 amps


q2 2sc1735 100v 0.5a 0.8w 55-300hfe 130mhz
512-KSC2383YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17
q3 2sa850 100v 0.5a 0.8w 55-300hfe 130mhz
512-KSA1013YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17 (R=60-120, O=100/200, Y=160/320)


Q5 2sd712 512-KSC2073TU
q6 2sc945a eCb 50v .15a .25w 300mhz 40-700hfe
512-KSC2383YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17

d8 mz-140 512-1N5244B Fairchild 14 V, 0.5W Zener
d9 mz-130 512-1N5243B Fairchild 13 V, 0.5W Zener
d10 LZ230 512-1N4748A Fairchild 22 V, 1.0W Zener
d11 LZ230 512-1N4748A Fairchild 22 V, 1.0W Zener

awr-164
c19,c20 4.7uf 50v 647-UPW2A4R7MDD 4.7uf 100v $0.14
c17,c18 47uf 16v 647-UPW1V470MED 47uf 35v $0.16
c24,c25 47uf 25v 647-UPW1V470MED 47uf 35v $0.16
c11,c12,c15,c16 220uf 80v 647-UPM2A221MHD 220uf 100v $1.02 ea
c13 220uf 35v 647-UPW1V221MPD 220uf 35v $0.28
c23 2200uf 35v 647-UPW1H222MHD 2200uf 50v $1.49 ea

 

[matt gholson]

Wow thanks, I wasn't sure if it even could be rebuilt. I'm in Harrisburg IL. which is close to the bottom, there are small handful of us that don't live in the Chicago area.

 

[tsd71]

If you are going to attempt the repair make sure not to put too much heat on those solder pads they will come up easy because of years of heat on that board

 

[Watthour]

Count me among that handful of "downstate" residents, even if Chicago is south of me.

Your missing turnover knob is readily available from various sources, so that's not a real problem.

There are some general rules which should be reviewed before anything unfortunate happens. TSD's point about heat is critical. An appropriate solder iron is essential. Other important items are clean boards, a clean and well tinned solder tip, the use of flux paste (even for for desoldering), and a high enough temperature to work quickly and minimize the time heat is applied.

Whatever you might do, do not unwrap any of the wire-wrap connections on the posts attached to the boards. If they MUST be removed, desolder and remove the pins with the wire wrap intact. If possible, simply release more wire from the plastic looms and clips and move the boards carefully to expose the areas where you may need access.

Construct a dim bulb tester for the purpose of limiting input line current when the unit is tested. Directions can be found in various threads here at AK.

BEFORE ordering any repair parts, review the common recap and repair parts list(s) for the SX-980 and consider placing one order to save shipping costs and frustration. Hint: Spending a few extra dollars to have a few spare components is often a good idea.