Great videos. One suggestion. Spray some contact cleaner on the adjustment pots before you tweak them. The wiper has been sitting in the same spot since factory and the carbon trace is for sure pretty dirty around it. This is why it's jumpy around the required measurement spot. It will make your adjustments much easier.
Nice repair! Thin cardboard - like the kind used on the back of writing pads - cut in strips and used with contact cleaner works well for cleaning contacts. Old style "Ruby Red" erasers work well - the newer type white erasers do not.
The glue on the bottom of caps was used to hold larger components in place until they made it to the wave soldering process machine, and you would see smaller caps than those "snap caps" also glued. Between the machine that handles the board, and any movement while the board is handled beforehand, it just insures parts are held in place until the solder cools. If you notice how all of the solder joints and exposed traces have the same liquid looking "flow" to them, that definitely looks like a wave soldered board.
I have the same amplifier that is blowing one of the three fuses on the power supply side and even if I unplug the amplifier section the fuse still blows. Any ideas where to start looking?
I just finished working on a TFM-6C that had this same symptom however what I found was two problems. The relay driver circuit gets it's power from a single diode rectifier through D707 and a small 10uF capacitor C708. The circuit couldn't pull in the relay because C708 was shot, probably from the terrible ripple from the half rectifier circuit. I replaced C708 and the relay started working. When I search for this solution I found similar discussions in some forums. For the relay contacts a pink eraser definitely worked for me and you can see from the PCB traces that only the N.O. contacts are used so I just focused on cleaning the back side contacts. I too searched for a replacement and ran across the 1335P relays listed on ebay here www.ebay.com/itm/Guardian-Electric-A410-363734-12-Relay-1335P-Series-12VDC-Coil-/362716676702 however from the photo that center contact sure looks oxidized to me so I choose to just clean what I got. Now I hope to put this back into service to power some Atmos speakers.
Love the video. Good work! I don't usually comment but I have to say those heatsinks are some of the best I've seen. Nice thick aluminum on the front reduces hot spots a lot near the transistors.
That glue was just "standard operating procedure" back in the 1970s . The main problem is that a lot of the glue can become conductive over time and actually cause shorts on the boards. It makes a huge mess also
Just wish the video had more of the finished repaired product shining (Amplifying) after the repair was completed, and maybe hearing the amp through a system with a nice pair of floor standing speakers, grooving through some LP's........ Dire Straights, Led, maybe even some Coltrane. Great video though, and I appreciate your sharing of your knowledge. DM.
The contacts we are looking at at 10:10 are NOT the ones that connect the speakers. You need to address the "normally open" contacts which are only engaged when the coil is energized. The contacts shown here - we need to be looking at the "back" side, and the matching ones closer to the rear. Those are the ones.
Would love you to write more notes in the 'notes' section. Love these videos, but a summary of what you are doing would make them 10/10. Thank you for sharing.
