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  1. #201
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    Check out this video for testing transistors.
    https://youtu.be/KGcoOETCaEQ

    sent from Utah.
    sigless.

  2. #202
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    Well, I think I scared it back to barely working.

    Read some stuff online and tried out a grounded vs groundless power connection. Grounded had the hum, groundless eliminated the hum when connected. Maybe a ground loop issue then? Tried to play music on it and got zero response.

    Today I cracked it back open and checked all the transistors I could find, everything seemed to check out. Checked again for ac at the sub out with the rca shorted and nothing there. Reconnected it to a different receiver, no hum and I'm getting some music. Definitely quiet even with the gain cranked all the way up, but it's playing. Maybe an issue with the speaker itself?

    It also may have noticed that I picked up a 12" sub at Costco for $170. That thing vibrated my balls nicely at 50% gain. Wife wanted me to turn it down within 30 seconds.

    I still need a sub for another room and I like the enclosure for this one, so I'm not ready to give up yet.

    Sent from my Pixel 4 XL using Tapatalk
    I've concluded that DJSapp was never DJSapp, and Not DJSapp is also not DJSapp, so that means he's telling the truth now and he was lying before.

  3. #203
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    Nice. I like the persistance. Check the ohms of the speaker itself. Not sure if it should be 4 or 2, but something close to either of those (or 8, less likely) and it's probably ok. Try moving the cone in and out carefully, and see if there is any scraping in where the coil is.

    sent from Utah.
    sigless.

  4. #204
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    Quote Originally Posted by basinbeater View Post
    Nice. I like the persistance. Check the ohms of the speaker itself. Not sure if it should be 4 or 2, but something close to either of those (or 8, less likely) and it's probably ok. Try moving the cone in and out carefully, and see if there is any scraping in where the coil is.

    sent from Utah.
    Not that. 8 ohms impedance per spec, 8 ohms on the reading. No obvious sounds of scraping or scratching either, but it's hard to exercise the cone. It's a downward firing sub with a plank below it



    Sent from my Pixel 4 XL using Tapatalk
    I've concluded that DJSapp was never DJSapp, and Not DJSapp is also not DJSapp, so that means he's telling the truth now and he was lying before.

  5. #205
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    Electronics! Falling into the geek rabbit hole.

    Not sure how but these seem to keep showing up

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    Local guy made a good deal on this STR-7045 and some Realistic Nova 7bs. So old but it all still sounds so good. These 2 are well matched together.

    Currently listening to the new King Gizzard on it.
    Last edited by dfinn; 11-23-2020 at 02:00 PM.

  6. #206
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    I like the old Sony stuff. It was such high quality it was the stuff that laid the groundwork for the late 80s when Sony meant quality.

    sent from Utah.
    sigless.

  7. #207
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    Snagged a new project yesterday for cheap. Rotel rb-1090 power amplifier. 380 watts per channel rated at 8 ohms. A monster. Dual mono construction, with each channel getting a dedicated 1.2kva transformer and huge capacitance. One channel works ok, other is in protect. But the unit has seen better days, smells like ass, and news a refresh. Going to repair the bad board, put new caps throughout (except for the huge monster power supply ones.)
    Should make for a pretty badass subwoofer amp, or turn a tidy profit. Fix it, play with it in the house, decide if it's a keeper or not. Thing is a goddamn beast!

    I do have. Avery nice krell showcase 5 home theater amp if anyone is looking for the good stuff. Has had the proper input board capacitor repair to take care of a common failure point on these, as well all t channels having their bias adjusted. Mag deal @$1100.Click image for larger version. 

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    sent from Utah.
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  8. #208
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    Big caps.
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    sent from Utah.
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  9. #209
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    What are those rated for? Probably not a good idea to lick your finger and find out by feel!!

  10. #210
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    22,000uf 100v rated. Rail voltage on this sucker is like 96v. Big time power supply.

    sent from Utah.
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  11. #211
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    Properly cleaned up and ready for supplying juice!
    All the copper hardware and copper bars, and even that top plate is solid copper, easy to clean with a but of salt vinegar and a wire brush. Rinse, and dry. Click image for larger version. 

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    sent from Utah.
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  12. #212
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    Clean......Click image for larger version. 

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    sent from Utah.
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  13. #213
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    My 70's Marantz 2238b made a series of super loud pops. Opened the case to find this. Hopefully the board is ok but there's some char. I can replace components but I'm not sure I'll be able to find a board if it's bad.

    Thoughts?

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    life ain't guaranteed, love your people while you can

  14. #214
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    That sure looks to me like something was leaking out of the large capacitor. The transistor that scorcher the leak behind it may or may not be ok, doesn't look exploded. Have to get in there with a multimeter.
    Second if there was large popping, you need to check the output transistors. Oh yeah, check the fuses. That thing needs a refresh

    sent from Utah.
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  15. #215
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    Bought a non functional cd player yesterday for $10, just cause it was close to the rc car store. Tray was not working, it would open and immediately close. Fixed that by finding cracked solder joints on the microswitch that tells the microcontroller that the tray is open, and thus shuts the motor off. Reflowed the joints and added some fresh solder. So now it plays, but it intermittently skips after a minute or so. That tells me the laser is probably fine, and that the tracking is off. Fixed the tray, and will tackle the power supply capacitors that filter the power to the laser focus, tracking, spindle motor, and sled motor this evening. Hopefully that clears up the problem. Nice looking player, with decent sound quality (until it skips). Luxman dz-122.

    Viva, here is that nak sr4a in action. I listen to it everyday for hours at a time. I love it.

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    sent from Utah.
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  16. #216
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    Whelp, dove into another project instead tonight. Since my mouser order arrived... Great service by those guys by the way. Every time. Fast accurate, good. Anyway, I sold some guy a krell preamplifier, and he was trying to beat me up on price, which was annoying since I had brought it to him, (it was very close to the rc car store, again... He.) And finally he said, how about a busted amplifier for $50 off price, ok, since I'm a sucker for broken stuff, I said sure, what is it, a Linn lk85. Supposedly pretty well regarded chip amp. So being the sucker I am, I grabbed the box without even checking it out, and brought it home with me. Indeed it was busted. Both chips had basically blown up. So I ordered a couple new ones, took it apart, and the eparta arrived today. Put the new chips in, repaired a couple of burned traces, and put it back together. Fired it up with a dim bulb tester, and...Bam! It works. Removed the dim bulb tester and took some measurements. Dc offset nice and low around 3mv on each side. Clean sine wave coming out at a few different frequencies, and then tested with a speaker. All good.

    See my new toy? Measuring the input signal in blue, and the output in yellow...

    I am going to head back downstairs and hook it up to the basement system and see how she goes.
    Check it out...
    Linn LK85 chip amp.
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    sent from Utah.
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  17. #217
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    Decent deal here... Not mine. But these are so good someone should grab it.
    https://www.facebook.com/marketplace...9510009554784/

    sent from Utah.
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  18. #218
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    Quote Originally Posted by basinbeater View Post
    I've not done much with surface mount soldering, so this will be an interesting challenge.
    If you don't have some already, some thermal tweezers are a godsend for surface mount stuff. There are always-hot ones for reflow and removal as well as quick-heat ones for installation.

  19. #219
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    Gonna have to get some smt stuff. But not until I finish the next project. Just grabbed a apt holman preamplifier. Needs a lot of work, but is in excellent cosmetic shape. It's gonna get all new semiconductors, and capacitors, and a few key matching resistors. Click image for larger version. 

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    sent from Utah.
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  20. #220
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    Nothing ground breaking here, but small personal victory in getting my new vfd to output from my arduino! Fkna!
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    sent from Utah.
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  21. #221
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    Haha! Progress! Still waiting for a multiple input relay switching board to show up on the slow boat from china, and then I can program the arduino to switch inputs, and I will program the display to show whichever input was selected. Should be a single pushbutton affair. Pretty stoked I got the display to work. It's a little bright, but than can be adjusted in the arduino code pretty easily. I was scared of it, so it sat on the shelf for a month, but, it works! Yay, even the kids are pretty impressed. Wife, not so much, "when are you going to fix _______ ?"

    The amp is a gb150d in case you couldn't tell, and it should be good for 150 watts per channel, but my transformer is a bit undersized, so this one is probably only good for 100, but have good headroom. It sounds very good, a little warmer than the honey badger it is sitting on top of. It is a mosfet diy amp developed by Greg ball. Click image for larger version. 

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    sent from Utah.
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  22. #222
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    Couple more construction pics.
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    sent from Utah.
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  23. #223
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    One thing I love about arduinos is the abundance of sample/premade code out there. I'm an okay programmer (classes in html, visual basic, c++, matlab, etc years ago) but if I can spend half an hour searching for code similar to what I need, look at the syntax and figure out what's different than what I've used in the past, edit, and test instead of spending 10 hours making it all from scratch then I'll take that as "easy."

  24. #224
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    Yep. I'm waiting on the input board, but have already written code that will allow me to cycle through inputs with a single pushbutton. Most of it was copied from someone else's code. Arduino is kind of neat.

    sent from Utah.
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  25. #225
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    My apt holman preamplifier that arrived just before Christmas got a fairly thorough going over. It arrived non functional. I repaired the power supply, replaced all electrolytic capacitors, replaced all opamps with a more modern model, cleaned all the pots, replaced the old relay with a more modern low signal relay on a perf board, and troubleshooted the mute circuit to figure out why it didn't work. Relay would buzz and not solidly engage. This last part was a chore because the mute circuit in my unit did not match the service manual schematic or the schematic on the bottom of the case. So I had to draw it out. After looking at it for a while, I decided to flip a couple parts around to go against their pcb markings, and now it works beautifully.
    Great sounding unit. Top dog preamp in my house right now.
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    sent from Utah.
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