What did you last repair??

[nigelwright7557]

Repaired a new design of a model railway dcc shuttle controller.

I trailed the internet for information on dcc before starting to try and get a working circuit and working software.
Bare pcb's turned up and I populated the pcb.
Couldnt get the loco to move.
SO went back to internet to get some clues.
Turns out it needs AC and not switched DC which i had used.
So a new fixed pcb made.
Managed to get it to move but only in one direction.
Turns out wit hdcc the loco has a acceleration and deceration routine.
What was happening was when I sent reverse command it was slowing down and stopping but before it could go backwards it got another command to go forward !
So increased cycle time and this time it went both ways.
Then after I added current overload circuit it kept overloading randomly.
Loads of noise on 12 volt power supply due to loco.
So decreased load sensing resistor by factor of 2 and now its fine.

[wiseoldtech]

I finally got around to finishing up doing service on my neighbor's Technics RS-1500US reel tape deck.

The machine needed a thorough cleaning, re-lubing, and repair to the audio board - some lousy PUTZ with a screwdriver from hell apparently got inside and twiddled almost every adjustment pot - damaging several in the process.

Now, however, she sings sweetly again, up to spec, all the leaky caps are gone, and set up for Maxell and RTM tape bias.

If you don't know what you're doing, and don't have the proper tools and test equipment, stay the hell out of stuff, it makes my job 100X more difficult.

[gmphadte]

I bought a Rising brand AM/FM radio literally from a dumpster just because I like the long tuning dial. It must be over two decades old. Being so old, I did not power it with 220 VAC, instead used 48 volts AC for couple of days so that the capacitors get reformed. Next, I used 115 volts AC for a day. When I connected 230 VAC, it started working.

And the project which was supposed to be for a long time ended in 4-5 days.

gajanan phadte

[nigelwright7557]

I have been working on a model railway digital command control shuttle system.
It sends out commands as +/-15vdc to the track.
I managed to get the comms working and can move train back and forth and change the speed.
I couldnt get the software right for changing trains ID number.
Trawled the internet relentlessly for information on data packet sequence.
Eventually I joined a pro model railway group who have designed all sorts of DCC equipment.
They passed on a pdf showing required data packets.
I input these to my software and it worked.
The comms software is quite interesting. To keep bits correct width I had write a serial shift register algorithm.
Just bit banging the outputs wasnt accurate enough.
I have to create a bit structure then send out bits one at a time on 2 phase pins.

Built a new JLH1996 class A amplifier.
On first power up output went to positive rail.
After a long visual inspection I spotted a driver transistor had a blob of solder between two pins. Serves me right for buying cheap Chinese solder.

[duplex]

A Quad 303 power amp, beautifully designed.

Needed to be cleaned thoroughly. Also new caps, resistors, trimmers, input and output sockets.

Wonderful warm and live sound after all was done and connected between my Rotel preamp and the Tannoys.

[kodabmx]

After realizing I had no sound because I had switched plate and cathode, I got to work on why I had LF instability where a loud peak (quickly crank volume from 0 to full to 0 again) would make it motorboat. As an aside, the 6F12P is a remarkable tube indeed. Vhk was over 600V, but the damned things still work!

I ended up making it stable by changing one of the RC poles (the PI to driver caps) from 1.4Hz to 0.31Hz (0.22uf/510k is now 1uF/510k) and that solved it. It still has an LF wiggle or two on those loud excursions, but it damps itself.

[kodabmx]

Oh and the top cap came off a good 6P36S so I took one from one that arced over and fixed it

[e3k]

fixed no sound issue on Yamaha htr 6040 when using digital optical signal input. after many unsuccessful settings i resorted to a factory reset of the amp and suddenly i get sound via digital input.

[poynton]

Arcam Alpha CD 6 with the usual problems.

Replaced the tray gear wheel and belt.

Also reset the turntable height.

It now plays all cds and sounds great.

.

[Eric]

Just finished repairing a Marantz AV9000 processor from circa 1999 that was holding down the DD/DTS duty in my family room system. Bought it on ebay in the early 2000s for $150 because it had problems. The problem at the time was a broken connection between the RCA jack for the surround channel outputs and the PCB. Fixed these up and I had a nice preamp on the cheap.

Then, in 2009, it failed on me and I just repaired the same problem again this week. The symptom was blowing PSU fuses. Not right away, but over time (hours to days). At first I thought it was bad caps, but this turned out not to be the issue. Very careful inspection with a 10x loupe and a bright light revealed hairline cracks in the solder joints on the bottom of the main PSU board. The specific problem was with the ribbon cable headers that go through-hole and are soldered to the board. The solder joint on several of these connections cracked and was causing arcing and burning that was causing the circuit to draw extra current in an effort to maintain its power supply. This doubled the current flow through the slow-blow fuse and caused it to open.

After removing old solder with a wick and applying new solder and cleaning the flux from the board on each of the ribbon headers on the PSU board, it's up and running again! No more dead fuses or error messages on the display panel.

Hopefully, this can help someone else trouble shoot a piece of gear that really doesn't need to be replaced...