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
safesphere
Have you downloaded the Sevice Manual from Vinyl Engine?
It is comprehensive....and has a trouble-shooting guide.
Safesphere, You seem to be a fairly competent trouble-shooter, just based on what you've already done. When I first saw your post, I thought right away you must have a problem with the switch. I am told they are prone to malfunction mechanically. But if you're sure the main power switch is OK, you might look at any of the other switches on the panel. They may be wired such that any one of them can cause the failure mode you are experiencing. Think of it this way… at least your TT101 runs. Are there any other faults in its function? Because you seem to know how the switch is wired, I assume you already have downloaded the Service Manual, as Halcro correctly suggests.
Yes I have the service manual, thank you. All other switches work fine. The only other potential issue with functioning is that, when the TT starts, it first overspins and then comes down to 33.33. On startup the first measurement after zero is higher than 33.33. It is inconsistent. Usually it is between 34 and 45, one time I saw over 70. Even when it is 34 I still see the platter spinning faster, but slowing down before the digits appear. The next number is usually 33.33 or slightly higher, the following one is always 33.33. This effect is less noticeable at 45. I also hear some motor noise on startup only that is clearly related to overspinning. I have access to another copy of TT-101 that does not show this behavior. I can try measuring transistor voltages, although it is physically challenging with the platter mounted. I don't have an oscilloscope other than through the PC sound card. Where can I get a good one at low cost? Thanks!
Here is an excellent oscilloscope for little $

Ebay

Best of luck

Peter
Just note that likely you need a set of probes for the suggested oscilloscope.
Unfortunately, the TT101 is very complex. Mine has nearly driven me nuts until I stopped fretting about it (because I realize that I also own 4 other great turntables that perform flawlessly, and it is of little consequence to me if my TT101 is a pain in the ass). Any of the hundreds of solder joints can have gone bad over the 30 or more years since they were built. Re-soldering suspect joints is a place to start. Another occult source of problems is those beige-colored multi-pin connectors. inside those connectors one may have a cracked wire or bad solder joint that is not accessible for inspection. I am about to ditch one of them and just directly solder the wires to the pins in hopes of curing a very elusive intermittent issue I have with mine. I was able to determine that tugging on the harness that goes to that connector can induce the failure mode I am trying to cure.
I have measured the voltages on some transistors at different speeds. I can see that pushing the Stop button triggers the following sequence of transistors (per the circuit diagram on page 38 or 39 of the service manual): 629 through 626 and 624, but not 625. The voltages on 625 are off, the same at any speed (12V on C or E and 11.3V on B), and don't depend on VR646. The voltage on the other side of R650 is 0.6V. This makes me think that X625 is gone and needs to be replaced, but I'm not an expert and would appreciate if someone could please confirm my conclusion. Thanks! -Alex
If you are not already seeking help elsewhere,you may find a teck hanging out on Audiokarma or diyaudio.
Safesphere, Wish I could help, but you've already gone further than I in parsing out that circuit. Early on in the repair of my unit, I gave it to a very competent pro who found no issues with the ICs or the discrete transistors, after he replaced all the electrolytic capacitors. I own a 'scope but have never applied it to repairing the TT101, because the problem is very intermittent and elusive in the first place.
Safesphere, I am bumping your thread. I did some re-wiring on my TT101 over the weekend, also found a bad electrolytic capacitor on one of the PCBs that are mounted under the top cover. (This was the only original lytic that we failed to replace on the first go-around, and it's the only lytic to be found under the top cover.) In the process of "improving" the wiring integrity, my other goal, I screwed up something. I need to ask you about the order of the wires in one of the connectors on that board. I hard-soldered them to the male prongs, because the connector was very loose. Now I fear I may have gotten the order incorrect. I will post the parts number for that connector, and maybe you can check yours for a reference. (The wiring is color-coded, as you know.) I turned what was once a rare intermittent problem into a consistent problem. Aaarrrggghhh!!!
Safesphere and anyone else with a dismantled TT101,
The connector in question is nearest to IC810 on the Crystal PC Board Assembly, TDC-7B. This PCB is located under the top circular piece that surrounds the platter. TDC-7B is depicted on page 31 of the owner's manual. The order of the four wires going into this connector, as I have it, is: brown, (space), orange, yellow, green. Please check, if you can do it without much trouble.

Upon second look, I think I've got it correct, but I am grasping at straws, trying to figure out what I did that could have worsened my problem. I cannot find anything else that could be causing my TT101 to upchuck. Thanks.
Lewm,
I find it useful to take lots of digital photos before I work on equipment. Quick and easy and can save a lot of time.
I did just that. Unfortunately I had unplugged this particular connector before taking a photo of that part of the PCB. Anyway, I hope Safesphere or some other TT101 owner responds, but if not, I do have the service manual which with some effort can be used to confirm the color codes of the wires. Actually, I am nearly certain I made no mistake, just grasping at straws here. Very weird.
After re-soldering the eyelites & running fine for 6 months or so, My TT-101 has started having same issues with the stop button. Did you come to a fix for it?
My own TT101 turned out to have a tiny crack in one of the PCBs which was finally diagnosed only after what had been an intermittent problem became a constant problem, enabling JP Jones of Fidelis Analog to sniff it out and repair it.  But the defect in function of my TT101 was not like that reported here.  Mine would come up to speed for a minute or two, then exhibit inaccurate speed for about 30 seconds, then crash.  This problem came and went at first (the definition of "intermittent"), moving the turntable to various parts of my house would either cure or cause the problem, probably because moving the turntable was causing the PCB to flex where it was cracked, causing a short to come and go.  JP tells me that he has since serviced other TT101s, and cracks in the PCB are not uncommon.  

My TT101 and I have been happy together for about 2 years now.  I use it regularly in rotation with 3 other turntables in two systems.

@gary7
 
My TT-101 has started having same issues with the stop button.


Knock on wood, perhaps the resident expert will comment.
@lewm   How is it possible to crack the pcb alone?
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.
@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.
It’s hardly a main stream item anyway, these days or even when it was current.
on the other hand, the TT101 and its ilk are now pushing 40 years old.
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. 

@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
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. 
I can refurb 2.5 SP-10MK3 in the time it takes me to do a single TT-101 right.


I have no doubt .... the pcb of the TT-101 is a real curse for the time spent looking for faults.
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?
@lewm 

Does this mean that the TT-101 if it is not placed in a heated and dehumidified environment makes the whims like children? Wowww
Ummm.... Best-groove, what are you trying to prove? No one would contest the fact that the TT101 is temperamental.  Least of all, me. So, I don't get it.  Unless you're just trying to be funny, which is fine.

It's also a very fine sounding turntable when all is well.
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.
Just relax and enjoy it, is my advice.  I do believe that once these initial and endogenous issues have been dealt with by someone like JP, probably all will be well.  But I have back-up tt's, just in case.
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

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
You can’t complain about that Gary.....😘
@gary7  

It seems an excellent result, plus the pot does not turn slightly backwards after the stop as I saw in several videos.  ;)
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.
@gary7

does the selector work to display the rpm that is placed under the plate?
 You mean the Run/Hold switch? Yes, it does.
@gary7I

saw the video, I could be wrong but I think that once the speed of 33.33 Rpm has been reached, the display should remain locked at the speed and not restart.It would serve the opinion of TT-101 owners working as @lewm 
I could be wrong but I think that once the speed of 33.33 Rpm has been reached, the display should remain locked at the speed and not restart.

You're wrong. Not in this mode
Hats off to JP Jones at Fidelis Analog. Reminds me of when I was a tech in the 80s and finding the elusive crack always made my day!
Post removed 
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


Move the switch to Hold and it will stay steady 33.33 or 45.00.
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.
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.
I always found the run and hold functions a strange function
to include and have left mine on the hold also.
Question. Since the adjusting of the quick stop, as per the SM, requires using records to add weight to calibrate, would using a record weight throw this off?
@gary7     


did you take pictures at the points where you intervened to get a good repair?
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...