Help with Troubleshooting - Suddenly working/not working [resolved]

[LegitBatman]

Hey all! I recently bought and built the SEX amp without issue, and I am in love. However, a few days ago, it was running then suddenly died, and would not turn on again. I turned it over and redid the resistance checks, and the resistances of a number of terminals with a * for its value was overlimit. I thought it was a soldering joint problem, so I redid all the solder joints I could, but still the issue remained. I just couldn't figure out what was wrong. Just when I thought I'd give up and come back another time, it suddenly started working again. I'm worried that the issue will return to haunt me, so I thought I'd reach out for help. Anyone know potentially what could be going on?

- Sean T.

[Mucker]

If you have an additional power cord, try it and make sure it's firmly seated in the amp socket. I have used power cords where the contacts seem a bit too far recessed into the plug and make bad or no contact. Some just need to be pushed in with more force.

[ccmccull]

If I remember correctly, the star means very high resistance. So OL is probably okay. I would start chopstick testing. Given that the whole amp dies, it sounds like it's a loose connection close to the input power, likely before or in the power supply section.

[2wo]

If it happens again, check if the tubes are glowing.

[LegitBatman]

The tubes stop glowing when it stops working, that's how I noticed it died. The thing is, for example, Terminal 33 was OL when it stopped working, but when it was working again Terminal 33 had a reading in the MOhms. So from my limited knowledge I believe it's a part that is dying (but I'm not sure which).

[Doc B.]

OL and Megohms are not that different. Best bet is to go over the IEC inlet connections and the power switch. Sometimes the power switch can be damaged from overheating when soldering. That can create an intermittent condition. There is a video on the Bottlehead YouTube channel about soldering the switch.

[Paul Birkeland]

The resistance check are meant to help you examine whether it's safe or not to turn your kit on for the first time and aren't really helpful here.

You'll need to measure the DC voltages of the amp when it's acting up.  Either you'll find that all the high voltage terminals pop up to a higher voltage than they should be, or they rocked down close to 0V.  Each of these results points to a completely different part of the circuit, so it's important to collect this data before going much further.

[LegitBatman]

Thank you for all your help everyone.

I ordered the IEC inlet and power switch, although off of AliExpress (hence the delay in arrival), and soldered it on (I tested the resistance and continuity of the parts and it seemed fine). Now it's not turning on at all. The heating filaments of the tubes do not turn on.

The resistances seem fine (again), and so I recorded the Voltages at the different terminals.

2: 477 DCV
3:  0 DCV
4: 0 DCV
5: 0 DCV
6: 477 DCV
7: 477 DCV
10: 477 DCV

This is the measurements for one side, but its the same on the other side.

H2, H5: 6.5 DCV
H3, H6: 3.6 DCV
H4, H7: 0 DCV

I live in Canada, so my outlet is 120V. I tested the transformer and that seemed to be working fine.
I have no idea what could be wrong with this, I've tried testing for values, the resistors seem fine, but my multimeter is having trouble measuring nano-farads of capacitance. Any help would be appreciated, struggling with this for a bit now.

Thank you all for helping,
Sean Tao

[Paul Birkeland]

The high voltages at the H terminals tell us that this low voltage DC supply is not making it to the tube heaters.  Perhaps the 0.1 Ohm resistor isn't well soldered on one end?

[LegitBatman]

Yes! That was it! Thank you so much! I guess I must've missed it resoldering everything because it was buried so deep.

Thank you all for your help!

Best,
Sean