@gibsoniana
great who knows how to do it, unfortunately it's not my job.
great who knows how to do it, unfortunately it's not my job.
JVC TT-101 Won't Stop
The Stop button on my recently purchased QL-10 doesn't work. It worked at first after the TT warmed up, but then quit completely. I since have replaced all 37 electrolytic caps on 3 boards, but it made no difference. The power voltages are correct. The button itself is fine and shorts pins 6 and 9 of the P8 connector on the main board, but the motor doesn't stop. What could be wrong? Any particular transistor or adjustment? Please help! -Alex
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conductor geometryit would be sufficient to replicate the awg of the internal cables, I see no difficulty because they do not have shielding. As regards the pcb I see that lately an ebayer sells the originals for Technics sp 10MK2 at prices between 350/450 € Those who could replicate these or those of the TT-101 could do a good business by selling them at less cost. |
Yes you would need someone with enough knowledge to design PCB properly but the making of them is easy once designcompleted, and not so expensive. R&R of the IC's I agree is not easy and not without risk. Acquiring a supply of these would make this a go for me. Calibration, service would be much simplified and these beasts would survive much longer this way. |
It'd be great but you'd want to shoot yourself before you finished. There would be many pitfalls. Some of these circuits are affected by lead length, just to begin with. Also, it is a trick to get a multiple pin IC off a PCB and then successfully transplant it to a second PCB and have it work. Plus, you'd have to have the new PCBs made in advance, of course. It would be a heroic effort, either way. |
Hard to get a good pics as the eyelets are small, silver bumps of solder. Some you really have to hunt for. If not mistaken, the SM on vinylengine has a schematic of the board that shown the eyelets connecting points in dark grey, you can use it to map them out. https://www.facebook.com/photo.php?fbid=2270251446319444&set=a.185305328147410&type=3&th... |
I'm too lazy to look at the video you quote, but the switch for "run" or "hold" makes no change to function quality. It only alters the read-out of the tachometer, in the ways that you have already discovered. I found the "run" display to be a bit crazy making, if you look at it for an extended period. I like "hold"; you can see what the tt is doing at a glance. |
best-groove ahhh ook no problems; but this then? It remains locked means that is that improvement? https://www.youtube.com/watch?v=-Rqmmcms1Tc Not sure what the improved version is. But it does start different than mine when he powered it on and pressed the 33 play button. The decimal point LED blinks several times when it powered on and then counted up to lock on 33.33 and stayed there. Wonder if it was a design change. |
You're wrong. Not in this mode ahhh ook no problems; but this then? It remains blocked means that is that improvement? https://www.youtube.com/watch?v=-Rqmmcms1Tc |
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Oh, I'm very happy this worked. My thinking is that one or more of the eyelets that involves the stop sequence from the 1st solder go-round did not get a good dose of solder and it finally started having intermittent control issues. The platter drift before was not too terrible, but now it comes to almost a dead stop. Very happy indeed. |
Well, trying to decide what to do with my TT-101, I pulled it out to have another go at the eyelets. I especially paid attention to the ones around the VR646 & VR647 pots that adjust the quick stop. Put it back together and ran for several hours testing the stop button in both 33 & 45. Seems to be fine, for now. It actually is stopping better. Before the platter had some drift after I hit the stop button. Maybe.....for now. https://www.youtube.com/watch?v=wIhIO7uoPY4 |
Got back with Dave Brown at
modularsynthesis.
These are his thoughts. Dave Brown, Dec 23, 11:52 PM It’s been a while since I have looked at the schematics and I was looking for something in common between all of those. My gut reaction is a connector. Tin corrodes and becomes intermittent. I’ve also seen failures mostly on the single sided phenolic boards but without plating it would happen on this board also. On a normal PCB with plating, the connector pins are held firmly to the board. Without plating they are only held on by the rear pads since you can’t solder the front pads since the connector covers them. You can never get the connector absolutely tight to the PCB and the leverage of the pins will rock them. The runs fracture right along the connection to the soldering. It would exhibit the kind of behavior you are seeing and is exasperated by temperature differences.
What I do for repairs is use epoxy to glue the connector to the topside of the PCB and on the bottom scrape away the solder mask about 3/15” from the pad and jumper the connector pin over to the fresh copper.
Typically you can see the connectors move a bit when you rock them.
This makes more sense than a random trace crack or a cold solder joint in that there is constant stress on the pins with the cable tension.
The connectors going to the front panel PCB makes the most sense. I think there is a front panel PCB. It’s been a while.
Dave |
Ummm.... Best-groove, what are you trying to prove? I do not want to prove anything I'm only slightly worried if my TT-101 will be repaired; I'm not going to want to keep a dry and warm place just for him, but I'm also amused because I will have for the first time a very metereopatic electronic product. |
I think we all agree that the TT101 is fussy. That’s one way in which this hobby requires a relaxed approach. For my part, I can only thank JP for the excellent work he did on my unit. Once JP educated me on the genesis of the issue with my TT101, I put a little space heater in my basement man cave, I set it to heat the room just enough to keep the temperature above 65 and control the humidity somewhat. I want say that I have had no problem since doing that, but wouldn't I be asking for trouble? |
Only cable issues I've seen have been due to people soldering the wire wraps, which causes a stress point and leads to very easy breakage. The board headers are delicate to, as pressure on the pins will delaminate the traces. Have to be very careful with those. I pull them to apply hot glue underneath to reinforce them. Doesn't help much, but I helps. |
@jpjones3318 Of course ... the TT-101 is 40 years old but other turntables that have the same years as the TT-101 have few or no problems even in the joints of the welds; maybe the PCBs of other turntables are not igorscopiche? I am thinking, for example, of the usual Technics SP 10 and others of the past. The TT-101 from what I have seen has a motherboard with tracks only at the bottom and some tracks on the upper side; There are several individual cables that pass through the pcb from one point to another in the upper side. I consider very little reliable multi-wire connectors that move not having a clip that keeps them still, the same I think for the cables become too rigid with the passage of time.I am inclined to replace the multi-connectors with Molex or other types of mini-connectors and, only where it is possible to replace all the cables .... then we will switch to the damns solderings |
On Lew's unit there was a very long scratch under the solder mask. In this pic you see the very corner of a crack in the solder filet (center) at the ~8 o-clock position. If you follow the trajectory you can make out the scratch. http://fidelisanalog.com/wp-content/uploads/sites/3/2018/12/LM-TT101-Crack1.png Once the mask was scraped away you can see that the scratch actually cut clean through the trace, and that the little corner of solder which cracked was the only piece making electrical contact. http://fidelisanalog.com/wp-content/uploads/sites/3/2018/12/LM-TT101-Crack2.png The boards on these units are very hygroscopic and haven't stood the test of time, nor has the solder. With the 101 I now vacuum clear every single joint and re-solder fresh. The riveted vias take a bit of skill as they trap gas and bubble so you have to get the temperatures right and have patience to get a joint that hasn't blown out, and also doesn't have excess solder. For testing I flex the board approx 30deg in all directions while the unit is running and the drive output is on the scope to see if it causes any glitches. If it does, which it will, there are still bad joints that need sorted or an issue will develop down the road. This is a unit where best practices need adhered to - don't mix old and new alloy, clear all conformal coating to avoid contamination, proper solder filets to prevent pad/trace cracks etc. I can refurb 2.5 SP-10MK3 in the time it takes me to do a single TT-101 right. |
@lewm I have read a lot in the world of the problems that happen to this turntable and I have to note that all problems are the same and similar; maybe you were unlucky with the break of the pcb and I have not read of other cases equal to yours but never other turntables like this have had a lot of problems like the TT-101. Turntable that sounds good (when it works) but so delicate too delicate and problematic ... it is easy to understand it by reading the defects that happen. |
I think JP would agree that the most likely story is that the crack was there since it left the factory or that the PCB swells and contracts with changes in humidity, thus rendering it susceptible to cracking at areas were expansion and contraction are constrained by the many fasteners that hold the boards in position. The latter hypothesis is consistent with my observation that it behaved differently (prior to repair) when it sat in our kitchen or a repair shop vs when it was set up in my basement audio system, where temperature is cool and air is moist. My own TT101 came to me as part of a QL10 (TT101 chassis + plinth + UA7045 tonearm). The whole thing was "like new" when I bought it, possibly suggesting that it had had a problem from new. I purchased it very cheaply, described by the seller as "broken", on faith that I could fix it or find someone else to fix it. |