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Little Dot MK8SE / MK6 Super Mods (All verified mods are on first page)
Sep 25, 2016 at 2:22 PM Post #1,981 of 4,154
It could even be a pinched wire on underside.
 
Sep 25, 2016 at 4:27 PM Post #1,982 of 4,154
maxx134 said:
It could even be a pinched wire on underside.
Click to expand...


Yes, it could be all of those, so looks like the board will come out and that's not going to be easy!
 
Sep 27, 2016 at 4:16 PM Post #1,983 of 4,154
Check wiring just that one negative signal wire.

you need to see if possible to observe if that wire is pinched or soldered on two points instead if one.
Use a dentist mirror and flashlight to look inside..
:p
 
Sep 27, 2016 at 5:19 PM Post #1,984 of 4,154
maxx134 said:
Check wiring just that one negative signal wire.

you need to see if possible to observe if that wire is pinched or soldered on two points instead if one.
Use a dentist mirror and flashlight to look inside..
:p
Click to expand...


I was thinking of using a dentist's drill to remove those tight screws lol. I finally managed to loosen them with a new screwdriver so hoping to remove the board tomorrow now so I can have a look and see what's what. It must be something like that wire!
 
I won't be using the dentist's mirror and flashlight....... too many painful memories
wink.gif
.
 
Sep 27, 2016 at 5:56 PM Post #1,985 of 4,154
Must be careful with those black screws as they can strip easily with a screwdriver that not exactly right size.
I have two on bottom cover I had to drilled out the screws on.
 
Oct 1, 2016 at 1:29 PM Post #1,987 of 4,154
Just checked everything on the reverse and it's all looking good, including the wire, soldering, nothing touching, connections are good.
 
I checked the pins again and pins 3 and 5 are grounded on the bad circuit. Given that pins 3 and 5 are connected in the same circuit on the good side then then clearly if one of these is grounded in the bad circuit it will affect the other. So I'm trying to investigate further to find out where the grounding is.
 
Oct 1, 2016 at 11:55 PM Post #1,988 of 4,154
Post a pic of the area on both sides so we can compare solder joints for irregularities.
If not the wire and tube is not connected, then most likely a soldering issue..
 
Oct 2, 2016 at 12:03 AM Post #1,989 of 4,154
Signal output of that tube goes only to output wiring,
and also runs in board back to the gain switch,
thru the resistors next to it,
So that gain switch area also needs observation.
 
Oct 2, 2016 at 7:28 AM Post #1,990 of 4,154
Inside right hand (bad) circuit : cathode bypass/resistor, coupling cap, WCF, anode resistor connections.
 


Inside right hand (bad) circuit : -ive output connection.
 


Both right hand circuits : cathode bypass/resistor connections.
 


Both right hand circuits : heater wire connections.
 


Outside right hand circuit : cathode bypass/resistor, WCF, coupling cap, connections.
 


Outside right circuit : anode resistor connections.
 


Inside right hand (bad) circuit : anode resistor, WCF connections.
 

 
Inside right hand (bad) circuit : cathode bypass/resistor, anode resistor, WCF, coupling cap connections.
 

 
Headphone output socket
 


Outside right hand circuit : WCF, anode resistor connections.
 


Outside right hand circuit : anode resistor connections.
 

 
Outside right hand circuit : cathode bypass/resistor, coupling cap connections.
 


Gain switch.
 


Let me know if you need more info.
 
Oct 2, 2016 at 9:06 AM Post #1,992 of 4,154
sonictrance said:
  Looks like the Rifa cap lead is shorting, or very close to it, with the 300 ohm grid resistor.
 
Other than that I can't see anything off.
Click to expand...

 
Thanks Sonic. It's quite well clear from a different angle, although the insulation could be better.
 
I've checked the 4 mods in the path of the bad circuit, and of the coupling, WCF caps, anode resistor and cathode bypass, both the anode resistor and cathode bypass are grounded, but so are they in the OK left hand circuit so I'm still wondering!
 
Edit: I just looked again and you can see by the curve of the bottom wire a tiny blob of solder, but it is only touching the board so could not short I don't think.
 
To summarize: everything is the right way round, connected up correctly, soldering looks good and there's no touching wires or anything, so what do I do now
confused.gif
 ???
 
Oct 2, 2016 at 12:31 PM Post #1,993 of 4,154
baronbeehive said:
  These are the results of the continuity test having tested a good left hand circuit, and both right hand circuits where the problem lies:
 
The tests all agree with each other except for the following results:
 
1 - The suspect middle right hand circuit shows continuity between pins 5 and 6
 
2 - The suspect middle right hand circuit shows continuity between pin 3 and the 330 ohm resistor
 
3 - The outside right hand circuit shows continuity over its coupling cap
 
I've double checked this and this appears to be somewhere where the problem must be if anyone has any ideas.
 
This is in addition to the wiring anomalies at the output XLR's identified earlier.
Click to expand...

 
Quote:
baronbeehive said:
   
I've just checked the circuits again with tubes out and everything is as before with tubes in, but there are a couple of addtional points to add to the above which I missed yesterday:
 
4 - The suspect middle right hand circuit shows continuity between pins 3 and 6
 
5 - the suspect middle right hand circuit shows continuity between pins 2 and 6
 
6 - the suspect middle right hand circuit shows continuity between pin 5 and cathode bypass/330 ohm cathode resistor
 
7 - the suspect middle right hand circuit shows continuity between pin 3 and cathode bypass/330 ohm cathode resistor
 
8 - the suspect middle right hand circuit shows continuity between pin 5 and 330 ohm anode resistor
 
9 - the suspect middle right hand circuit shows continuity between pin 6 and 330 ohm anode resistor
 
If anyone can see a pattern in this let me know!
 
Now I'm going to test the wires.
 
Edit: I've just seen a pattern, the problems are in both plates and cathodes, apparently not the grid.
 
Edit 2: Just tested the output XLR's from the positive and negative points on the board. All good except the right hand negative. I've revised my results yesterday so they are as follows now:
 
1 - There was continuity with pin 1 of right hand XLR output from right hand -ive on the board.
2 - There was continuity with pin 2 of right hand XLR output from right hand -ive on the board.
3 - There was continuity with pin 1 of left hand XLR output from right hand -ive on the board.
4 - There was continuity with pins 1 and 2 of right hand XLR output testing just the XLR's (not from the board).
 
This post summarizes the test results to date, I've spent most of the day on this.
 
What makes me think it's the output wiring is because I've checked the 4 runs of 3 core wires and they are connected correctly, (except for the lack of an earth wire in one of them as I mentioned earlier which was the same as stock wiring). That leaves the 6 output wires............. HOWEVER the left and right hand +ives are correct and the left hand -ive is correct and the left hand ground is correct and therefore the continuity with the right hand pin probably indicates ground on the right hand pin therefore the other right hand pin is probably correct .......... so the output wires are probably correct? (Or these 2 pins could be reversed).
 
I believe the connections are all correct so if I can find out where the short is that could be the answer because it is all the power in the right -ive connection that is draining out and could explain why there is practically no voltage going through the middle right grid pin 1.
 
You can compare the above anomalies with the good circuit:
 
1 - pin 3 has continuity with pin 5
2 - pin 7 has continuity with pin 8
3 - pin 2 has continuity with 330 ohm anode resistor, WCF and cathode bypass/cathode 330 ohm resistor
4 - pin 6 has continuity with cathode bypass/cathode 330 ohm resistor
5 - cathode bypass/330 ohm cathode resistor has continuity with cathode bypass/330 ohm cathode resistor and 330 ohm anode resistor
6 - WCF has continuity with 330 ohm anode resistor
 
I don't know what to do next to try to find the short if it is that.
Click to expand...

 
Just speculating, but if there was a short between tube pins 5 & 6 that would explain most of the test results above. For example:
 
Point 1 (above) - The suspect middle right hand circuit shows continuity between pins 5 and 6 (because I think there may be a short there)
 
Point 4 (above) - The suspect middle right hand circuit shows continuity between pins 3 and 6 (because pin 3 has continuity with pin 5 in the good circuit and pin 6 may be shorting with pin 5)
 
Point 6 (above) - the suspect middle right hand circuit shows continuity between pin 5 and cathode bypass/330 ohm cathode resistor (because pin 6 has continuity with cathode bypass/cathode 330 ohm resistor in the good circuit and pin 6 may be shorting with pin 5)
 
Point 7 (above) - the suspect middle right hand circuit shows continuity between pin 3 and cathode bypass/330 ohm cathode resistor (because pin 6 has continuity with cathode bypass/cathode 330 ohm resistor in the good circuit and pin 6 may be shorting with pin 5 which is connected to pin 3 in a good circuit)
 
Point 8 (above) - the suspect middle right hand circuit shows continuity between pin 5 and 330 ohm anode resistor (because cathode bypass/330 ohm cathode resistor has continuity with cathode bypass/330 ohm cathode resistor and 330 ohm anode resistor in a good circuit and pin 6 has continuity with cathode bypass/cathode 330 ohm resistor in a good circuit and pin 6 may be shorting with pin 5)
 
Point 9 (above) - the suspect middle right hand circuit shows continuity between pin 6 and 330 ohm anode resistor (because cathode bypass/330 ohm cathode resistor has continuity with cathode bypass/330 ohm cathode resistor and 330 ohm anode resistor in a good circuit and pin 6 has continuity with cathode bypass/cathode 330 ohm resistor in a good circuit)
 
Point 2 (above) - The suspect middle right hand circuit shows continuity between pin 3 and 330 ohm anode  resistor (because cathode bypass/330 ohm cathode resistor has continuity with cathode bypass/330 ohm cathode resistor and 330 ohm anode resistor in a good circuit and pin 6 has continuity with cathode bypass/cathode 330 ohm resistor in a good circuit and pin 6 may be shorting with pin 5 which is connected to pin 3 in a good circuit)
 
Sorry to be repetitive but I'm trying to be as clear as possible. I'm only speculating because I don't know about circuit diagrams and don't know which way it goes through the circuit. But I'm sure a circuit diagram could be drawn to make sense of this.
 
Oct 2, 2016 at 1:11 PM Post #1,994 of 4,154
Sorry to be repetitive but I'm trying to be as clear as possible. 
Click to expand...

I'm struggling to read your posts to be honest, baron. 
 
I can say this though. Only the heater pins, pin 7 and 8, should have continuity between them. If any other pins show continuity it's not good. Now that you have the board out you could start de-soldering suspect components around the problematic tube until there's no more short.
 
Oct 2, 2016 at 3:09 PM Post #1,995 of 4,154
sonictrance said:
  I'm struggling to read your posts to be honest, baron. 
 
I can say this though. Only the heater pins, pin 7 and 8, should have continuity between them. If any other pins show continuity it's not good. Now that you have the board out you could start de-soldering suspect components around the problematic tube until there's no more short.
Click to expand...

 
Ha ha.... thanks for trying anyway Sonic, I can't understand what I said either!
 
My point was that if there was a short between tube pins 5 & 6 then it would explain the test results I had for the bad circuit. However I can't quite see how there could be a short there.
 
Edit: There's also continuity between tube pins 3 and 5 in a good circuit, not just 7 and 8.
 
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