Voltage test troubleshooting and unilluminated LEDs [resolved]

[RyanNoo]

Hello,

I completed the mainline, but unfortunately failed the final voltage test. The power transformer, power supply, and resistance tests all passed with no problems. In addition to the incorrect values for the voltage test, the pair of LEDs on the B sides of the C4S boards are not illuminating. I double checked and they are oriented correctly.

I went back over the instructions from the power supply test onwards and could not find any obvious miswirings or bad joints. Any ideas on what could be going wrong here?


Voltage test:
+275vDC on the Power Supply Board    275V    368V
+6.3vDC on the Power Supply Board    55-65V  59V
-6.3vDC on the Power Supply Board     50-60V  53V
IA on the A side C4S Board                  275V     368V
IA on the B side C4S Board                  275V     368V
Breg Regulator Board (both sides)         220V  a 2.9V
                                                                   b 2.9V
-reg Regulator Board (both sides)         0V      a 0V
                                                                   b 0V
Kreg Regulator Board (both sides)    8-12V     a 1.2V
                                                                   b 0.5V



Thanks,

Ryan

[Paul Birkeland]

This is very likely to be solder joint problems based on the non-existent Breg voltages. The MJE571A transistors in particular need a fair amount of heat to solder properly.

[RyanNoo]

Thanks, Paul. I'll resolder the MJE571A transistors and report back.

Also, the tube on the A side is unilluminated.

[Paul Birkeland]

That is the shielded twisted pair of wires going to pins 4 and 5 on the 9 pin socket.  Definitely all the tubes need to glow for the amp to work properly, but that is definitely not the only issue.

[RyanNoo]

I resoldering the MJE571A transistors, but am still having the same issue. During construction I initially had the transistors in the wrong placement and removed them using a decent amount of force. Do you think this could have internally damaged the transistors?

Fortunately resoldering pins 4 and 5 on socket A fixed the tube issue and it is now glowing.

Next I will try reflowing all of the joints in the kit unless you have any other suggestions.

[Paul Birkeland]

I would post some build photos. The 2.9V or so that you're getting at Breg would suggest that there's either a catastrophic wiring error that you've made which is shorting the output of the high voltage regulated supply, or it's just a soldering issue.

If you have to pull MJE5731As out of those boards and you don't have a good solder vacuum, the boards themselves can easily be destroyed in the process.

[RyanNoo]

I may have found the issue, but could still use some help.

I reviewed the instructions to check the wiring and also resistance checked every non-colorcoded resistor manually using my voltmeter. I found that the C4S board R1 resistors on the A sides of the boards have values of 37.4 killoohms while the manual says a 37.4 ohm resistor should be used. The resistor is navy blue and labeled 37.4 K1% 2213. I assumed that I mixed up two resistors, but all the other resistors in the build appeared to be correct and I do not see anything in the parts list for a 37.5 killoohm resistor.

Could this resistor explain the failed voltage test and unilluminated LEDs? Do you think this could have been a packaging error or am I still missing where this resistor should be?

Thanks again for all your help,

Ryan

[Paul Birkeland]

Well that would have taken a long, long time to find!  I let Eileen know that possibly we got sent (or ordered) the wrong part.  This kind of stuff happens from time to time and we can just send out some replacement resistors.  You can actually just solder the correct resistor across that one and thing will still work properly.

[RyanNoo]

Whew - I am glad I don't need to go over the whole build again. Hopefully the correct resistor will resolve everything. Should I reach out to Eileen to provide shipping info and the part ID?

[Doc B.]

Yes, I just verified that we were sent the wrong part, a 34.7K resistor instead of 34.7ohm resistor. This will affect the recent Mainline and Eros kits we have shipped. We will get the proper resistors on order today and ship them ASAP to anyone who ordered a kit recently.

[RyanNoo]

Thanks for the quick response Doc and Paul. I am looking forward to completing the kit!

[RyanNoo]

I swapped out the resistors and everything is working now. The amplifier sounds great -  a huge upgrade from my crack.

[Doc B.]

Glad to hear and sorry for the mixup. You can bet we scrutinized the heck out of the replacements we sent.