News: Trouble logging in? Log in from the login page.
July 08, 2020, 03:47:21 PM

Author Topic: Mainline Voltage check failure  (Read 77 times)

0 Members and 1 Guest are viewing this topic.

Offline photonwolf

  • Newbie
  • *
  • Posts: 2
Mainline Voltage check failure
« on: June 06, 2020, 06:56:47 AM »
Gentlemen,
I just competed the mainline assembly and the resistance checks are good.

Unfortunately, got the following on the voltage checks:

275VDC on PS board       313V
6.3VDC on PS board        6.3V
IA on A-side C4S board    312V
IA on B-side C4S board    312V
Breg on Regulator board  A-side 222V, B-side 1.7mV
-reg on Regulator board  A-side 0V, B-side 0V
Kreg on Regulator board  A-side 11.43V, B-side 0.7V

Obviously, the LEDs are lit on the A-side C4S board but not on the B-side, so it looks like one side is functioning.  I checked solder connections and found no obvious visual shorts on any of the solder joints.  I re-seated the 12AU7 and made sure the pins were not corroded.

I also did basic diode checks on the Regulator board transistors, the C4S transistors and LEDs, and they all seem to be fine, i.e., all e-b and b-c junction voltages measure the same (are symmetric) on the two C4S boards and on both sides of the regulator board. 

Any suggestions on where to look next are appreciated.

Alan


Online Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 13054
Re: Mainline Voltage check failure
« Reply #1 on: June 06, 2020, 07:42:46 AM »
Can you post some photos of what you have so far?  (including the top and bottom of that C4S board)

The LEDs being out on the B side is actually a bit of a good thing, as the 0V at Breg could normally mean that the output of the C4S is shorted, but in that case the LEDs will be lit and the MJE5731A would be pretty warm.  On the other hand, soldering issues in a C4S typically manifest as the IA/IB voltage matching the Breg voltage. 

I strongly suspect you have a missing jumper wire on the board. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline photonwolf

  • Newbie
  • *
  • Posts: 2
Re: Mainline Voltage check failure
« Reply #2 on: June 06, 2020, 09:45:03 AM »
Hi Paul,
Thanks for the quick reply.

Here are some images:

1) The underside of the B-side C4S board

2) The top view of the B-side C4S

3 The bottom of the Reg board

4) Reg board top view

5) Overview of full mainline


Online Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 13054
Re: Mainline Voltage check failure
« Reply #3 on: June 06, 2020, 10:13:05 AM »
In the first photo you posted of the high current C4S board, I would reheat all of those joints.  If you're using lead free solder, I would get leaded solder.  If you are using leaded solder, I would use more heat (45+ watt soldering iron or a station turned all the way up).
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man