A friend of mine has a B-52 Matrix 200 PA system he uses for small events and the volume pot busted. Adjusting the master volume would result in intermittent sound on, often way more on than wanted. Pity, as it’s a decent sounding rig for a small to mid-size room.
In this case the master volume pot seems to have failed internally – probably from getting smacked at some point, but according to the internet these units seem to have various other quality issues as well. Rather to be expected with this bad a solder job – pretty crappy wetting on most joints:
Anyway, nobody on the internet seems to have fixed this particular problem but it’s pretty simple: the Panasonic EVJ-Y15F03A54 is a drop-in replacement for the obscurely branded OEM part. The EVJ-Y00 and EVJ-Y10 series should also work – the Y10 is actually the exact match - but DigiKey didn’t stock it and you don’t need the threaded bushing in this application anyway.
Forgot to take good photos of the tear-down, but if you’ve been into gear before it should be pretty straight-forward:
- Remove the amp chassis from the case – screws on top (in the handle recess) and on the bottom.
- Unplug the ribbon cable to the DSP (effects) board
- Remove the six screws holding the edges of the front panel to the main chassis.
- Figure out how to lay the front panel on the workbench without yanking wires too much (or unplug the wires from inaccessible locations on the power board in the chassis – make sure you label which goes where, they’re both the same size plug)
- Take out all the screws on the front panel and remove the nuts from all the jacks – the front panel will lift off the circuit board so you can access the volume pot.
- Desolder the old pot (don’t overheat like I did and lift traces)
The vias came out with it… good thing we didn’t really need them.
- Solder in the new pot
- Reassemble in reverse order
If you can’t get the Panasonic for some reason it should be possible to use a standard dual 50K audio taper pot, as long as it will fit between the front panel and the circuit board. (Measure carefully!) Make careful note of the pinout in the Panasonic datasheet – it’s not what I would have expected. I did a quick trace back to the closest op-amp to confirm pinouts were identical, here’s the schematic:
The op-amps are standard JRC/NJM4558s but in SIP packages – took me a few minutes to find the SIP pinout.
So that’s pretty much it. It took me longer to find the replacement pot than it did to take the unit apart and replace it, and that was nearly more time with a screwdriver than the soldering iron. I also need to work on my desoldering skills, they ain’t what I thought they were.
One of the things I have been wanting to do almost since I got an electric guitar – over ten years ago – is to build some of my own effects pedals. I decided earlier this summer (2012) that I am actually going to do that, by golly, and not just true bypass mods and control switchboxes like I’ve done in the past. Real analog effects circuits this time.
Then I realized that I wanted a way to test things at my electronics bench without lugging my mega-ton 112 combo up and down two flights of stairs and decided I needed a practice amp first. I could buy one of those, I guess, but I want to build stuff – why not that, too? And I managed to do it for practically free. Continue reading
We had a power outage a while ago, in the middle of which someone needed to get out of the garage and… couldn’t. The door that needed to be opened was, naturally, the one that wedges itself in slightly when it shuts, so it jams the electric opener’s emergency release.
Further investigation revealed that a good hard judo-yank will release it (with a bang), but not everyone can do that. So I made a release helper – because almost anyone can step on a lever. The pictures pretty much say it all – just hook the custom specially calibrated clothesline to the release pull and step on the board.
This is one way to drill a hole without getting too much sawdust all over the place, even using a spade bit.
Fencing your woodchips with masking tape.
I normally reserve creating sawdust and messy things like that for the Shop For Big And/Or Messy Things, far away from my office/computers/electronics bench. However, the Shop For Big And/Or Messy Things is really cold in the winter and I was feeling wimpy.
I was sorting out a pile of old CDs this morning and found my first linux install discs, in spiffy looking cardboard:
They were researched, greatly wished for, highly anticipated, and a huge letdown. Continue reading
This past week I picked up a couple of cheap LED nightlights at Marden’s ($1.99 for a two-pack) and had to take them apart, of course, as I am a self-respecting geek, and because I was at one time mildy obsessed with running LEDs off line power. I guess that hasn’t quite worn off.
This all has led me to two conclusions:
- American consumers are suckers
- Chinese are either idiotic electrical engineers or brilliant social engineers, or both
Actually, both of those are not entirely deserved, nor totally fair, but read on for the full tear-down. Continue reading
Here are some photos taken from my Drive-To-Work collection, which (usually) are random photos of random things I’ve taken – you guessed it – on my drives to work and back. Bonus points if you know exactly where these are taken! Continue reading
Here are some photos from dusk at Spring Point in June, 2009. It’s a beautiful time of day at a beautiful place – even with the oil tankers. I’ve got a couple more tanker-free photos after the break.
Here’s some photos from the 2009 4th of July fireworks in Boston. Photos like these are difficult to come by with a slow point-and-shoot.
There is an odd social pressure to collect stuff. This may be due to our tendency to buy the latest and greatest in good consumer fashion, and it may be due to our belief that more information is good information and you can never have too much (not true). It is likely a combination of both and a variety of other factors which I have overlooked.
In any case, we both consume and store more and more information every day and most technology is concerned with getting it to you faster and cheaper, whether it be your smartphone, your media server, or Gmail. I think that is wrong. Continue reading