High voltage on IA and one LED not lit

Love Rhino · 3526

0 Members and 1 Guest are viewing this topic.

Offline Love Rhino

  • Jr. Member
  • **
    • Posts: 43
on: February 12, 2021, 05:19:27 PM
Hi helpful forum folks!

I have completed my build and passed resistance checks.  The only thing that might concern me on the resistance checks is 6 and 16 measuring 35k instead of the "might measure 25k" that the manual states.

When measuring voltage, I am getting a very high reading of 350 from IA.  I stopped measuring at this point to make sure I don't damage the amp.

The LED attached to A8 is not lit.  All other leds, including the other led on the A socket and both boards are lit.  The tubs all glow.  There have been no explosions as of yet, and I have not travelled back in time.  These are wins.

I have rechecked my wiring and visually inspected joints.  Any idea on an area of focus?  Thank you in advance!!!



Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19500
Reply #1 on: February 13, 2021, 07:07:31 AM
What's your AC line voltage?  Can you post some photos of your build?

350V at IA would either mean your in a 220V-240V mains country and you wired the amp for 120V (unlikely), or you have a loose connection in your amp causing weird voltage issues (nearly certain).

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Love Rhino

  • Jr. Member
  • **
    • Posts: 43
Reply #2 on: February 13, 2021, 12:47:10 PM
Line voltage was 119, and the initial voltage tests were in range, at 3.0, 3.0, 6.1, and 166.

In the pictures I do not have the low current board screwed in, to be better able to see the sockets.  I'm not surprised
 the A8 led isnt lighting, I really struggled with that little bugger; it was probably that hardest thing to solder in the build for me.




Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19500
Reply #3 on: February 13, 2021, 12:49:34 PM
I can't see much in your photos because they are tiny.

I would reflow every solder joint in the amp other than the power switch and the center post of the 9 pin socket.  This is what I do on pretty much any repair that I get and that resolves most issues.

What is the DC voltage at terminal 24?  How about 25?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Love Rhino

  • Jr. Member
  • **
    • Posts: 43
Reply #4 on: February 13, 2021, 01:18:31 PM
Paul,  thank you for your quick reply on a Saturday - you're the best.

DC voltage at 200 setting were 191 at terminal 24, and 0 at terminal 25.

I've adjusted the size of the photos, perhaps these will work better:




Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19500
Reply #5 on: February 13, 2021, 02:24:04 PM
DC voltages at 30 and 31?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19500
Reply #6 on: February 13, 2021, 02:25:40 PM
When you connect something to a terminal, you need to bend the lead up (for the lower terminals) or up and around for an upper terminal.  Just letting a component lead poke through the terminal and soldering isn't adequate and will lead to an amp that doesn't work.   This is in red text on page 20 in the manual.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19500
Reply #7 on: February 13, 2021, 02:26:46 PM
The resistor going to pin 7 on the 9 pin socket is untrimmed.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Love Rhino

  • Jr. Member
  • **
    • Posts: 43
Reply #8 on: February 13, 2021, 05:05:26 PM
DC voltages at 30 and 31?

192 for 30 and 0 for 31.

Getting to work on cleaning it up now :).



Offline Love Rhino

  • Jr. Member
  • **
    • Posts: 43
Reply #9 on: February 13, 2021, 05:12:47 PM
The resistor going to pin 7 on the 9 pin socket is untrimmed.

This fixed the led lighting.  Voltage on IA dropped to 259, so something is still off but it’s getting better.



Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19500
Reply #10 on: February 13, 2021, 07:34:29 PM
It would help if you listed the voltages for IA, OA, and OB on the large C4S boards.  It would help to have IA, IB, KregA, KregB, OA, and OB on the small board.

The IA voltage on any of the C4S boards will not be more than the voltage at 30 or 24.

What is your voltage at 32?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Love Rhino

  • Jr. Member
  • **
    • Posts: 43
Reply #11 on: February 13, 2021, 08:04:57 PM
Here is the full voltage check:

Low current c4s
IA 281
OA 264
KregA 0
BRegA 261
IB 327
OB 165
KregB 12
BRegB 327

High current c4s
IA 422
OA 249
bA 0
IB 0
OB 233
bB 248

Tip and ring are 0




Offline Love Rhino

  • Jr. Member
  • **
    • Posts: 43
Reply #12 on: February 13, 2021, 08:07:10 PM
Voltage at 32 is 465



Offline Love Rhino

  • Jr. Member
  • **
    • Posts: 43
Reply #13 on: February 13, 2021, 08:12:53 PM
The voltage for the board closest to the power switch measured slightly different.

IA 420 (about the same)
OA 325 (vs 249 on the board closest to the rca input)
BA and IB 0
OB 208 (vs 233)
bB 328 vs (248)



Offline Paul Birkeland

  • Global Moderator
  • Hero Member
  • *****
    • Posts: 19500
Reply #14 on: February 14, 2021, 05:17:08 AM
Yeah, you definitely have a loose ground wire in your amplifier.  Don't worry about actually having 465V at terminal 32, that voltage is only an indicator that things aren't well connected.

Reflow all of the solder joints, and whatever you do don't try to listen to it!

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man