Re-capping a spare 1200 I had and found the ground trace between C108 and C112 overheated, lost its top coating. In my 35+ years of working on these I’ve never seen this issue before on the boat load of 1200s I've dealt with, even the few with bad AN6675 motor drive ICs. This pictured PCB is out of a properly functioning unit when I pulled it. However, it was purchased second hand with unknown history. The whole PCB looks to be untouched and never been worked on. The surrounding electrolytic caps all tested ok.
Anyone ever see this issue before?
Anyone ever see this issue before?
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Interesting! The photo makes it look like it's just worn off, did you remove the green because it was obviously overheated... I.E., bubbling or burnt?
Haven't seen this before, no. (But I haven't been in many -1200)
Haven't seen this before, no. (But I haven't been in many -1200)
I went over the trace lightly with a scalpel. The coating wasn't blistered, but brown discolored. The silk screen lettering sort of protected some of the coating under it. There's no significant discoloring on the component side.
My only guess what could have caused it was the platter bearing being too dry and starting to seize, loading the drive IC to the point it was pulling too much current. Could have been from asking too much torque from the motor while someone was DJing with it. I just don't want it to cook the drive IC, which is unobtainium these days.
My only guess what could have caused it was the platter bearing being too dry and starting to seize, loading the drive IC to the point it was pulling too much current. Could have been from asking too much torque from the motor while someone was DJing with it. I just don't want it to cook the drive IC, which is unobtainium these days.
@6L6 The common thing which fails on these TTs is the drive IC and various capacitors. Most issues are down to cold solder joints with the common ones being around the main Vreg circuitry. I've never seen burnt traces on these things with only one exception, caused by an unqualified tech installing capacitors some backwards.
I've seen these things tossed across the room, used as weapons in club fights and still working somewhat. They're tough machines. Predictably, the arm bearings are the most fragile thing on them.
I've seen these things tossed across the room, used as weapons in club fights and still working somewhat. They're tough machines. Predictably, the arm bearings are the most fragile thing on them.
BTW, the small ceramic caps you see on the PCB are bypass caps I install on these things. It improves noise rejection from the main regulator, which tends to be on the loose side stability wise.
I've heavily modded one, and did some tweaks and an arm rewire to another. I've been in more SP-10 than SL-1200.
The main reg was replaced by a 317 in mine, not a hard mod at all. Have you ever done similar?
The main reg was replaced by a 317 in mine, not a hard mod at all. Have you ever done similar?
Yes, absolutely. I've done practically everything to a 1200 to bring wow / flutter down as far as possible. I've even designed a new magnet centering jig to get the platter magnet perfectly centered within the motor armature. There's also a magnetic bearing setup I designed to eliminate the platter thrust bearing.
As far as voltage regulation, I used a 317 reg in conjunction to an external transformer, but modified the external parts to get rid of the speed flare upon shutoff.
Used the SP10 extensively working in the broadcast tech sector. I can get similar performance out of a heavily modded 1200, but it takes very strategic mods to get close, most which require special machined parts not within reach of most diy people. Where the 1200 lacks most is the arm and the platter. The 1200 bearing can be modified to get lower rumble and noise floor than the best thrust bearing. I use a static electro-magnet controlled by a height sensor to adjust platter height ie. adjust VTA on the fly without the arm height adjustment. This dampens the arm resonance in the vertical plane along with a KAB fluid dampener. I can also compensate for warped records with it.
As far as voltage regulation, I used a 317 reg in conjunction to an external transformer, but modified the external parts to get rid of the speed flare upon shutoff.
Used the SP10 extensively working in the broadcast tech sector. I can get similar performance out of a heavily modded 1200, but it takes very strategic mods to get close, most which require special machined parts not within reach of most diy people. Where the 1200 lacks most is the arm and the platter. The 1200 bearing can be modified to get lower rumble and noise floor than the best thrust bearing. I use a static electro-magnet controlled by a height sensor to adjust platter height ie. adjust VTA on the fly without the arm height adjustment. This dampens the arm resonance in the vertical plane along with a KAB fluid dampener. I can also compensate for warped records with it.
Does this mean that you can dynamically (up to several Hz) modulate platter height? Very cool.
All good fortune,
Chris
@Chris Hornbeck Sort of, up to a point, yes. It tracks the vertical arm azimuth and platter height up to 16 hz, so it functions up to most arm resonance frequencies but the feedback circuit from the arm is still being refined. Sometimes it will still want to hunt a little to get back to true vertical center, as its right on the edge of positive feedback. The limits of the vertical platter servo can compensate for a .065" p-p warp at up to roughly 10 hz. The vertical coil current and platter load are the limiting parameters along with available spindle bearing travel and platter clearance to the inside deck. An unclamped 120 g record can allow for roughly 6 hz correction at up to roughly +/- .017" warp. I have to be very comfortable it will track a decent amount of warp reliably before I trust running my favorite Van Den Hull cart on it. Some will say a vacuum platter is easier to design, but a record can still have a substantial vertical warp from the pressing depth offset, something which can't be corrected by a vacuum platter.
This is all done with analog circuitry and optical sensors but I can't share any more due to the ongoing patent process. The other guy funding most of the project already has some interested in licensing once the bugs are worked out.
This is all done with analog circuitry and optical sensors but I can't share any more due to the ongoing patent process. The other guy funding most of the project already has some interested in licensing once the bugs are worked out.
So to get back to the PCB trace issue - I checked the 6675 motor drive IC and found Iittle heat sink compound on it. This wasn't the cause of the issue. It does show how hot this unit ran from DJ use and is a good indicator of hard use. I'm going to reinforce the trace with solder and move on. It should be fine after having still functioned properly with older caps and the like. I'll install a bigger heat sink on the driver IC and possibly the signal generator IC.
I just cleaned off and reinforced the suspect trace with solder and called it good. The rest of the 21V supply line will get LC decoupling to keep the strobe and speed clock signals off the output drive rail.
I'm running the little drop in reg from KAB for the 21V, but when I went to test it, the reg only put out 19V. The drop resistor in the voltage devider for the LM317 was out of tolerance. It was supposed to be 3k65 resistor, but measured 3k45, so I just bumped it to 3k9 and the reg put out the full 21V. It would have likely not made a difference but the main rail should at least be 20V. The manual calls for 21V,.so that's what I go by.
I'm running the little drop in reg from KAB for the 21V, but when I went to test it, the reg only put out 19V. The drop resistor in the voltage devider for the LM317 was out of tolerance. It was supposed to be 3k65 resistor, but measured 3k45, so I just bumped it to 3k9 and the reg put out the full 21V. It would have likely not made a difference but the main rail should at least be 20V. The manual calls for 21V,.so that's what I go by.
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I also decided to thicken the motor drive traces with solder to improve drive response. This also helps reduce the noise emission from the motor into the DC supply ground, aiding dynamic speed stability. The thin traces limit the available current from the drive IC. The traces are actually different in resistance to each other, so a slight W/F improvement can be expected.
I only do this on applications where the motor won't be loaded heavily from DJ use, as the resistance is designed into the motor to limit current to the coils. Despite this, the IC actually runs cooler under normal use.
I only do this on applications where the motor won't be loaded heavily from DJ use, as the resistance is designed into the motor to limit current to the coils. Despite this, the IC actually runs cooler under normal use.
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I followed your thread and I always wondered if the blank copper trace wasn't the result of leaking electrolyte.
@Netlist Well, if it was on top of the PCB it would be a possibility, but it was out of reach of any possible cap leakage. The other scenario could have been a shorting filter cap ie C108.
The TT this was out of did function correctly but as a complete rebuild I re-caped the entire board. I used Panasonic EB series for everything except the RC coupling drive dampening and the platter brake, on which Nichicon UES was used.
I can get W/F well under .06% RMS with several mods, which is better than even most Neumann cutting lathes. This is a very low number for an analog servo deck.
The most common oversight is that most dont pay attention to the drive magnet centering. If its even slightly out of round or center, W/F goes up quickly.
The platter bearing upgrade from KAB makes a big difference in these TTs. The rumble is more than 90 dB down compared to the 70 dB with the stock bearing.
If you dampen the entire chassis underside around the platter well, it greatly quiets any resonances. The one thing which is overlooked when dampening the chassis is the speed adjustment PCB. It rings like a bell untreated.
The TT this was out of did function correctly but as a complete rebuild I re-caped the entire board. I used Panasonic EB series for everything except the RC coupling drive dampening and the platter brake, on which Nichicon UES was used.
I can get W/F well under .06% RMS with several mods, which is better than even most Neumann cutting lathes. This is a very low number for an analog servo deck.
The most common oversight is that most dont pay attention to the drive magnet centering. If its even slightly out of round or center, W/F goes up quickly.
The platter bearing upgrade from KAB makes a big difference in these TTs. The rumble is more than 90 dB down compared to the 70 dB with the stock bearing.
If you dampen the entire chassis underside around the platter well, it greatly quiets any resonances. The one thing which is overlooked when dampening the chassis is the speed adjustment PCB. It rings like a bell untreated.
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Well, something very bad happened as I powered it back up through the KAB LM317 reg. The ground lug on the terminal strip was intermittent / loose (as pre-installed by KAB), so the reg went full open without the ground reference, putting full 35V on the AN6675 motor drive IC. It also took out the AN6680 control IC through Q201 receiving the full 35V. I'm NOT HAPPY.
This is why I usually solder everything instead of use those stupid bare wire insert barrier strips. I just wanted to test it quick before putting it together permanently, but now I'm looking at a lot of money. Buyer beware regarding these KAB reg boards. Mine wasn't even putting out the full 20 - 21V when I tested it first, so I had to change the adjust pin drop resistor. Now I get to replace some hard to find parts...
I usually build my own LM317 reg circuits, but I was trying to take the easy path and use a pre made reg. Honestly, the stock reg is more than adequate and a drawback of the LM317 on this turntable is speed flare when shutting off power (only important for DJ use, if that).
This is why I usually solder everything instead of use those stupid bare wire insert barrier strips. I just wanted to test it quick before putting it together permanently, but now I'm looking at a lot of money. Buyer beware regarding these KAB reg boards. Mine wasn't even putting out the full 20 - 21V when I tested it first, so I had to change the adjust pin drop resistor. Now I get to replace some hard to find parts...
I usually build my own LM317 reg circuits, but I was trying to take the easy path and use a pre made reg. Honestly, the stock reg is more than adequate and a drawback of the LM317 on this turntable is speed flare when shutting off power (only important for DJ use, if that).
Bummer...
If it were me, I'll search for a donor deck (Sold 'For Parts'). These IC's are next to impossible to find and if they are, at outrageous prices.
Of course, you'll need to be lucky that those IC's will still work.
If it were me, I'll search for a donor deck (Sold 'For Parts'). These IC's are next to impossible to find and if they are, at outrageous prices.
Of course, you'll need to be lucky that those IC's will still work.
Can we see a photo please ? I see KAB has skimmed my website and not realized that we were the first to use steel cases and they did not actually measure the original or modified turntable. I have retired now and am sad to see my previous good work has not been picked up by anyone.
I think I have both chips here in a box somewhere ?
I think I have both chips here in a box somewhere ?
Looks OK ? It should have a big o/p capacitor the absorb the motor current though.
If the ground wire had looped through the PCB it would been safe. I have a 19" rack on the bench with simply horrible screw terminal that are soooo badly manufactured.
If the ground wire had looped through the PCB it would been safe. I have a 19" rack on the bench with simply horrible screw terminal that are soooo badly manufactured.