Lasonic TRC-931 Repair & Restoration

vermouth

Member (SA)
Aug 15, 2018
54
12
8
Brazil & USA
I picked up a sad Lasonic TRC-931 that was in need of a few repairs. It was $70, but had a siezed power switch, was stuck on AM (broken gear), a broken tape deck, and was very hard to change inputs (another broken gear). I'll log what I've done so far:


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before

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Every square centimeter of it, inside and out, was like this

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Gear #1: Desoldered the switch with my Aoyue 474a++, cleaned out the switch and lubricated it with Super Lube

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Trommelmops' milled brass replacement gears to the rescue. I LOVE this kit, I got two gears and it comes with a milled tool for tightening the tiny bolt that attaches it. Beautifully engineered.

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Re-attached. The mod is easy if you are experienced at soldering/desoldering, but is absolutely not something for the inexperienced.

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Gear #2: also broken but not as bad I guess

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Trommelmops again. You need to file down the ends of the original metal shafts with a file. They were attached under pressure and that gives them a lip that needs to be removed before you can fit the new brass gears on

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Re-attached

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Recapped the radio PCB and started cleaning


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I really love how beefy the Lasonic 931 is, but its Chinese capacitors are garbage and are way past their specced lifespan at this point. I'm giving mine a full recap using long-life, 105C rated Japanese caps from Digikey. I'm matching the capacitance of the originals, but using much higher voltage rated caps, since those are what I have on hand from other projects

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The original thermal compound on the heatsinks was powder, so I replaced it. This is overkill, but I enjoy the process

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Spraying Deoxit in the power switch was enough to fix it

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Recapped the front facing/EQ PCB and applied more Deoxit in the sliders & pots

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I'm waiting on a few more caps to come in and then I'll re-organize the cables and she'll be done

https://www.youtube.com/watch?v=Ve-OWia2Un8
First test sounds excellent, to me at least. Couldn't find any proper boombox music on the radio, so jazz it is

After 8+ hours cleaning it inside and out, it's starting to come together
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Esther was a badass

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What's left: finish 10 or so caps left in the recap, do some more deep cleaning, track down antennas, find a battery compartment cover, get rechargeable D cells, and tackle the tape deck one day. I just use line-in for everything so tapes are a low priority. I feel like it deserves to have the deck fixed though.
 

soundsyztem

Member (SA)
Jul 23, 2015
22
1
1
Ohio
Nice work there. Your devotion to the craft shows. These boxes can be a test of ones patience to work in without a dedicated chassis to hold pcb’s and connected by a pile of wiring without quick disconnects. I had one with a bad gear and a disintegrated plastic shaft extension. I ended up selling as a project with those issues disclosed.