Just a heads-up, I am indeed back at UNT. I moved in Move-in day was last Saturday, and though I think most if not all of my stuff is up here, I'm not exactly settled in and unpacked yet. Also, like last year, because I am back at UNT, the posts will certainly be slowing down. Luckily though, I have a backlog (albeit small) of posts that I need to format and add pictures to, but will be able to put those out on a somewhat regular basis. Who knows, maybe I will post a picture of my room once I'm done.
Monday, August 27, 2012
Monday, August 20, 2012
Fixing the Marantz
As I'm sure you are well aware of, I am going to college at UNT, and am staying in the dorms on campus. Now as great as my headphones are, I still like to listen to music through speakers every once in a while, and the speakers on my laptop don't cut it by a long shot. Because of this, I decided to bring my stereo up from home: the wonderful, magical, beautiful Marantz 2230.
It may be from the 70's, and it may weigh over 30 lbs, but it sounds fantastic! Anyways, it worked great for the first semester and about half of the second, but then I noticed that something weird was happening: the left channel was getting quieter and quieter. I could compensate by adjusting the balance for a while, but the white noise due to turning it up so loud to compensate for the imbalance finally got so unbearable that I had to use headphones plugged directly into the computer for the rest of the semester. Finally, a few weeks ago, my dad and I decided that it was time to fix it. The first step was isolating the problem: we began by narrowing it down to the preamps, which made sense, as there was one for each channel.
Luckily, we had not only the user manual (which actually came with a schematic), but also the service manual, which had schematics for each section as well as different values the components should read. We narrowed down the problem even more, figuring out which transistor made the left channel so much quieter than the right one. We started by replacing that transistor. No dice. We replaced a couple of capacitors, still nothing. Luckily, I remembered that we had another Marantz above the office more or less for parts, so I went up and brought it back down. We decided to just go ahead and replace the entire preamp, since by this time we were tired of troubleshooting. We cut the preamp loose, and proceeded to replace the preamp. My dad had been lamenting the length (or lack thereof) of the wire when trying to probe the preamp, so we decided to make sure there would be the perfect amount of wire to lay flat while working. After spending quite some time on that, we plugged the stereo back in and checked the signals. Same thing: the left channel was way quieter. We did find it fairly odd that both preamps had the same problem, but the parts unit had been above the office for so long that we had no idea what kind of condition it was in. We decided to cut the other preamp free from the parts unit to test, and this time use clip leads to connect them instead of soldering before testing. We hooked all the wires up, and it had the same problem! By this time, we began to suspect that maybe the left channel preamp wasn't the problem. We then decided to do what we should have done at the beginning: bring out the other Marantz 2230 we had (and knew worked), and compare the levels. As I'm sure you have figured out by now, the left channel was the correct volume, and the right channel was too loud! Once we finally figured that out, it was a relatively quick fix of replacing the right channel preamp. We got it put back together, and I now have a beautiful and fantastic sounding stereo to bring to college in a few weeks.
Edit: When I said we replaced the preamp, I was actually mistaken. What we actually replaced was the entire preamp and power module.
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| The legendary Marantz 2230. |
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| Look at those big, beautiful preamps attached to the heatsinks! |
Luckily, we had not only the user manual (which actually came with a schematic), but also the service manual, which had schematics for each section as well as different values the components should read. We narrowed down the problem even more, figuring out which transistor made the left channel so much quieter than the right one. We started by replacing that transistor. No dice. We replaced a couple of capacitors, still nothing. Luckily, I remembered that we had another Marantz above the office more or less for parts, so I went up and brought it back down. We decided to just go ahead and replace the entire preamp, since by this time we were tired of troubleshooting. We cut the preamp loose, and proceeded to replace the preamp. My dad had been lamenting the length (or lack thereof) of the wire when trying to probe the preamp, so we decided to make sure there would be the perfect amount of wire to lay flat while working. After spending quite some time on that, we plugged the stereo back in and checked the signals. Same thing: the left channel was way quieter. We did find it fairly odd that both preamps had the same problem, but the parts unit had been above the office for so long that we had no idea what kind of condition it was in. We decided to cut the other preamp free from the parts unit to test, and this time use clip leads to connect them instead of soldering before testing. We hooked all the wires up, and it had the same problem! By this time, we began to suspect that maybe the left channel preamp wasn't the problem. We then decided to do what we should have done at the beginning: bring out the other Marantz 2230 we had (and knew worked), and compare the levels. As I'm sure you have figured out by now, the left channel was the correct volume, and the right channel was too loud! Once we finally figured that out, it was a relatively quick fix of replacing the right channel preamp. We got it put back together, and I now have a beautiful and fantastic sounding stereo to bring to college in a few weeks.
What I Would Do Differently
CLIP LEADS CLIP LEADS CLIP LEADS!!! Never again will I solder something like that again without first testing it with clip leads. I also would probably compare it with a known source if possible. Because it was important to compare known amplitudes, we used a function generator with the leads precariously clipped onto a headphone jack-to-stereo RCA cable. If I ever have to do something like this again, I definitely plan on making a BNC-to-stereo RCA cable; it would make the entire process much easier.Edit: When I said we replaced the preamp, I was actually mistaken. What we actually replaced was the entire preamp and power module.
Friday, August 17, 2012
Polycarbonate For the Control Panel
The thing I had alluded to in the last post was making a polycarbonate (Lexan) overlay for the control panel. This was worthwhile, if not necessary, for a number of reasons: First off, people are going to be touching the nice pretty white control panel with their grimy hands all the time, so you want to be able to clean it. If you only had paint, between the grimy hands and the cleaning because of the grimy hands, it would eventually wear through the paint. The other reason is similar: using an overlay allows you to put fewer coats of paint on, and I believe I have mentioned before as to how much I despise painting.
Now for the process of making the panel:
I started out by tracing out the shape of the panel, and cut it with plenty of room to spare. I then marked out where I was going to put holes for screws on both the panel and the overlay. When marking the screws, I put painters tape over approximately where I knew I would be drilling holes, then marked 1/2" in from each edge with my special 0.3mm mechanical pencil (everyone who knows me is disturbed by my love for them). The reason for the painters tape in case you were wondering is that it helps to keep marks off of the board, and also helps to avoid marring the surface from a misbehaving drill bit. After drilling the holes and countersinking, I peeled off the bottom plastic sheet, and fastened it to the board. After that, I used a flush trim bit and routed out each hole with my router table, using the hole in the panel as a guide. At this point, I was basically done; all I had to do was peel off the top sheet and I was good to go!
If I could, I would definitely mark the screws differently; once mounted, the panel bowed up between two screws, due to a mismeasurement. I would also like to do something different when fastening and routing the overlay. I got shavings of Lexan underneath the overlay and was afraid to do anything with them, because I didn't want to scratch anything with them. Next time, I would probably leave the bottom sheet on, fasten it, rout it, take it off, clear all the shavings, peel off the bottom sheet, then very carefully refasten it using the same holes. I would also not use it in a router table configuration; the router was full of pieces of Lexan, which was hard to get out. I would use a different bit, and use it in handheld configuration to let gravity take care of the stuff for the most part at least.
Now for the process of making the panel:
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| Cut and ready to mark. |
What I Would Do Differently
If I could, I would definitely mark the screws differently; once mounted, the panel bowed up between two screws, due to a mismeasurement. I would also like to do something different when fastening and routing the overlay. I got shavings of Lexan underneath the overlay and was afraid to do anything with them, because I didn't want to scratch anything with them. Next time, I would probably leave the bottom sheet on, fasten it, rout it, take it off, clear all the shavings, peel off the bottom sheet, then very carefully refasten it using the same holes. I would also not use it in a router table configuration; the router was full of pieces of Lexan, which was hard to get out. I would use a different bit, and use it in handheld configuration to let gravity take care of the stuff for the most part at least.
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