Troubleshooting Resistance Checks

[ksolis01]

I ran through the resistance checks and terminals 22 and 23 aren't giving the correct values. They should be *, fluctuating value, but instead when I probe each, the multimeter doesn't even respond to the probe. I tried re soldering all the immediate wire connected to the terminal and rechecked that those wires were in the right place. All the other resistance checks are good, just these two. Appreciate any help.

 

[Paul Birkeland]

No response is consistent with the note provided for the asterisk.  22 and 23 are your incoming line voltage, so not getting any resistance reading there is a good thing.

 

[ksolis01]

Ok. I only had time in the morning for the glow test. On the circuit board over the B socket on the A side of the board, both leds don’t turn on. I didn’t get time to voltage checks but where should I start troubleshooting because of those two leds.

 

[Paul Birkeland]

The voltage checks provide infinitely more information than "the LEDs don't glow".

 

[ksolis01]

The voltage checks provide infinitely more information than "the LEDs don't glow".

Got them.
Terminal    Voltage (DC)

Low Current C4S
IA        150V  (187.6)
OA 60-90V  (79)
KregA  3-6V  (1.947)
bRegA 150V    (188)
IB        150V  (148)
OB  60-90V  (55.2)
KregB  3-6V  (13.04 )
bRegB  150V  (148.1)

High Current C4S (D socket)
IA        190V  (192)
OA        150V  (148)
bA        0V  (0)
IB          0V  (0)
OB  90-110V  (82.5)
bB        150V  (148.1)

High Current C4S (B socket)
IA        190V  (188)
OA        150V  (186.9)
bA        0V  (0)
IB          0V  (0)
OB  90-110V  (0.025)
bB        150V  (0.044)

Headphone Jack
Tip          0V    (0.01)
Ring        0V    (0.04)

 

[Paul Birkeland]

Low Current C4S
IA        150V  (187.6)
KregA  3-6V  (1.947)
bRegA 150V    (188)
OB  60-90V  (55.2)
High Current C4S (B socket)
OA        150V  (186.9)
OB  90-110V  (0.025)
bB        150V  (0.044)

bB ties to OA with a red wire.  bB is 0.044V, OA is 186.9V.  They are not connected.

 

[ksolis01]

bB ties to OA with a red wire.  bB is 0.044V, OA is 186.9V.  They are not connected.

Ok, soldered that connection again. These are the only two value that change significantly and were the problems ones. They seem within range but the two leds I mentioned in my previous post still didn't turn on.

High Current C4S (B socket)
OB  90-110V  (95.9)
bB        150V  (186)

 

[Paul Birkeland]

Recheck all your voltages.  bB isn't going to be 186V without one of the Kreg voltages being off.  Also, bB should be extremely close to 150V. (within a volt or two)

 

[ksolis01]

Recheck all your voltages.  bB isn't going to be 186V without one of the Kreg voltages being off.  Also, bB should be extremely close to 150V. (within a volt or two)

KregA and  and KregB are significantly off, especially B.

Terminal    Voltage (DC)

Low Current C4S
IA        150V  (187.7)
OA 60-90V  (79.3)
KregA  3-6V  (1.936)
bRegA 150V    (187.7)
IB        150V  (148.1)
OB  60-90V  (54.6)
KregB  3-6V  (12.9)
bRegB  150V  (148)

High Current C4S (D socket)
IA        190V  (190.5)
OA        150V  (148)
bA        0V  (0)
IB          0V  (0)
OB  90-110V  (81.4)
bB        150V  (148.1)

High Current C4S (B socket)
IA        190V  (188.3)
OA        150V  (186.7)
bA        0V  (0)
IB          0V  (0)
OB  90-110V  (96.5)
bB        150V  (186.5)

Headphone Jack
Tip          0V    (0.01)
Ring        0V    (0.04)

 

[Paul Birkeland]

I would suggest flipping over the high current C4S board with the troubling voltages and reheating all of the solder joints on that board, as well as the socket under it. 

This builder had similar issues that ended up being resolved by reheating the solder joints, with particular emphasis on the center leg of each MJE5731A.

 

[ksolis01]

I would suggest flipping over the high current C4S board with the troubling voltages and reheating all of the solder joints on that board, as well as the socket under it. 

This builder had similar issues that ended up being resolved by reheating the solder joints, with particular emphasis on the center leg of each MJE5731A.

Ok, I reheated all the joints. However, when I connected it, something under both high current C4S boards started to smoke. Immediately disconnected it. On the B socket, the 237Ω 1/8 W resistor connecting B5 to B6 got burnt. On the D socket both 220Ω 1⁄4W connected to the ground lug intertwined got burnt.

 

[Paul Birkeland]

Can you show me pictures of that area on your amp.  Neither of those parts is under any thermal stress whatsoever, but a short on or around the socket could cause damage like this.

 

[ksolis01]

Hopefully this is enough photos. First 9 are the B socket. The rest are D socket

 

[Paul Birkeland]

I would wonder if the tube socket lug where the 237 ohm resistor connects got shorted to the black wire next to it.

Is this the wire provided with the kit?

 

[ksolis01]

I would wonder if the tube socket lug where the 237 ohm resistor connects got shorted to the black wire next to it.

Is this the wire provided with the kit?

Ye, the whole build is stock. Going to wait on getting the new resistors and then recheck all related wiring to try to find how the short happened.

 

[Doc B]

Hmm, peculiar. It appears that the B+ supplying the plate at pin 5 of socket B shunted current thru the 237 ohm resistor between 5 and 6.  Somehow the 237 ohm resistor been shorted to the heater winding, thus also taking out the resistors on pins 3 & 4 of the D socket, which tie from heaters of both socket B and D to ground, and thus would be the path to ground for the short.

So the question is how did the screen at pin 6 in socket B get shorted to the heater winding (pins 3 and 4 on both B and D)?

 

[ksolis01]

Hmm, peculiar. It appears that the B+ supplying the plate at pin 5 of socket B shunted current thru the 237 ohm resistor between 5 and 6.  Somehow the 237 ohm resistor been shorted to the heater winding, thus also taking out the resistors on pins 3 & 4 of the D socket, which tie from heaters of both socket B and D to ground, and thus would be the path to ground for the short.

So the question is how did the screen at pin 6 in socket B get shorted to the heater winding (pins 3 and 4 on both B and D)?

Got the replacement resistors today. I checked around that area and when I was resoldered that area to try to get rid of any bad solders, I melted off the rubber on quite a bit of the heater wiring. The first two are pictures of the black heater wire in the B socket. My wiring ended up pretty tight, and the desoldered black wire part nearest to the end (first two pictures) was resting on B5 terminal. I'll fix it tomorrow, and am just posting along with pictures to confirm that this is probably the cause. Don't want to connect it tomorrow and end up shorting the resistors again.

To fix this, would it be fine to solder on a bit of extra length using leftover white wire or some of the black and red wire from leftover heater wire and wrap electrical tape on all the exposed areas? The extra wire to loosen up the area and decrease the chance that something rest on something.

 

[Paul Birkeland]

In order to fry that screen resistor on the 7 pin tube socket, you would either have to have a freakish short inside the tube that would've damaged other parts, or the pin and/or screen resistor leads had to be touching one of the heater leads.

 

[ksolis01]

I taped up all the possible ends that could have caused the short and added the burnt resistors back. I went through all the voltage test and essentially got the results that I got before, the little variation was within the decimals. I already tried resoldering all the connection under the problem board. Just gonna resolver again I guess.

KregA and  and KregB are significantly off, especially B.

Terminal    Voltage (DC)

Low Current C4S
IA        150V  (187.7)
OA 60-90V  (79.3)
KregA  3-6V  (1.936)
bRegA 150V    (187.7)
IB        150V  (148.1)
OB  60-90V  (54.6)
KregB  3-6V  (12.9)
bRegB  150V  (148)

High Current C4S (D socket)
IA        190V  (190.5)
OA        150V  (148)
bA        0V  (0)
IB          0V  (0)
OB  90-110V  (81.4)
bB        150V  (148.1)

High Current C4S (B socket)
IA        190V  (188.3)
OA        150V  (186.7)
bA        0V  (0)
IB          0V  (0)
OB  90-110V  (96.5)
bB        150V  (186.5)

Headphone Jack
Tip          0V    (0.01)
Ring        0V    (0.04)

 

[kgoss]

Are all of your resistance checks right?  Don’t apply power again till all resistance tests pass. They are there to prevent damage when power is applied to a build with wiring problems.