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September 21, 2020, 09:49:34 AM

Author Topic: OA V problem [resolved]  (Read 282 times)

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Offline Alby0521

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OA V problem [resolved]
« on: August 02, 2020, 08:54:24 AM »
Hi

I just assembled and mounted the 2 boards and took the readings.
On A side I get:
IA: 525
OA: 297
Both are good values within the 10% for IA and 1% for OA

On D side I get:
IA: 525
OA: 295
The OA is out of range of 2 V. Is this acceptable?

I noticed that the manual has me wire pin A6 with OA of the A side board.
On the channel D the manual has me wire D4(specular of A6) to IB instead than OA on the D side.

Is this right?

Best

AB

« Last Edit: August 14, 2020, 03:59:15 PM by Paul Birkeland »

Offline Alby0521

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Re: OA V problem
« Reply #1 on: August 02, 2020, 08:56:49 AM »
Ps:

Also I just noticed that the small light (D1) on the B side of the board on side D of the chassis doesn’t light.

Any idea?

Best

AB

Online Paul Birkeland

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Re: OA V problem
« Reply #2 on: August 02, 2020, 09:27:47 AM »
295V is close enough.  This voltage is influenced by resistor tolerance.

The B side LED issue would have me asking what your voltage at OB is on that side, and whether you can perform the bias adjustment in the manual. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Alby0521

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Re: OA V problem
« Reply #3 on: August 02, 2020, 09:36:20 AM »
Hi Paul

I resoldered some joints on the board and checked the V again. The values I got were the same. Once I was doing so the 90.9 ohm resistor (90R9F) burst producing a spark.

I will need a new board. What is your take on this? I double checked all the connections and components and they are right where they should be.

The only difference between left and right is what I mentioned in the comment above regarding the manual info on pin A6 to OA and D4 to IB.

Any idea?

Best

AB

Online Paul Birkeland

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Re: OA V problem
« Reply #4 on: August 02, 2020, 09:43:27 AM »
The 9 pin socket wiring is different between halves.  You will also find that the Kreg wires go to opposite terminals and pin 3 will be grounded on one socket and pin 7 will be grounded on the other.

Perhaps you could post some photos of the top and bottom of the offending board? 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Alby0521

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Re: OA V problem
« Reply #5 on: August 02, 2020, 10:02:20 AM »
Here the pics.

Any idea? Should I replace the entire board?

Best

AB

Online Paul Birkeland

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Re: OA V problem
« Reply #6 on: August 02, 2020, 10:42:15 AM »
Yes, you should replace the board, all the parts on the board, and all the zener diodes on the terminal strip mounted underneath it. 

On that board, the only thing that jumps out is that the red wire leaving OA isn't well soldered on the other end. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Alby0521

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Re: OA V problem
« Reply #7 on: August 02, 2020, 10:47:31 AM »
Hi

Ok thank you for the advice. I’ll order the part and mount them back.

Best

AB

Offline Alby0521

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Re: OA V problem
« Reply #8 on: August 03, 2020, 03:28:04 PM »
Hello Paul,

I ordered the board and parts plus the 6 diodes. I'll be mounting it this weekend.

What do you think should i do to avoid what i went trough yesterday? Reading the various posts on the forum the possibility to explode resistors on the board are the following:
- Wrong Diodes orientation (not my case)
- Touching with multi-meter probe multiple contact points on the board while testing for V (Which I think it's what happened to me)
- 10uf cap touching chassis and or strips? not sure on this one.

All i'm asking is  if there is anything else (different from the above) i should make sure before i install the new board.

Thanks in advance.

Best

AB

Online Paul Birkeland

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Re: OA V problem
« Reply #9 on: August 04, 2020, 05:44:28 AM »
When you measure OA and OB, you can just touch the metal tab on each MJE5731A on the board to get those voltages, you'll probably find that helps avoid this issue.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Alby0521

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Re: OA V problem
« Reply #10 on: August 04, 2020, 12:33:25 PM »
Hi Paul

You mean the metal tab i circled in red in the attached picture or the 3 pins on the bottom of it?

Best

AB

Online Paul Birkeland

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Re: OA V problem
« Reply #11 on: August 04, 2020, 12:54:58 PM »
Yes, what you have circled.  If you have the heatsinks installed, there's still a little bit of it exposed at the top (the heatsinks aren't great electrical conductors).
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Alby0521

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Re: OA V problem
« Reply #12 on: August 04, 2020, 01:11:18 PM »
Awesome.

Thanks

Offline Alby0521

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Re: OA V problem
« Reply #13 on: August 14, 2020, 03:37:54 PM »
Installation completed. It sounds like a champ!

Offline vince

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Re: OA V problem [resolved]
« Reply #14 on: August 16, 2020, 01:25:41 PM »
Hi

I just assembled and mounted the 2 boards and took the readings.
On A side I get:
IA: 525
OA: 297
Both are good values within the 10% for IA and 1% for OA

On D side I get:
IA: 525
OA: 295
The OA is out of range of 2 V. Is this acceptable?

I noticed that the manual has me wire pin A6 with OA of the A side board.
On the channel D the manual has me wire D4(specular of A6) to IB instead than OA on the D side.

Is this right?

Best

AB

Hello;

I just assembled the same section and found a similar result.

Side  IA   OA
A      511  295.3
D     510  298.6

Note that 300(0.99) = 297 and 295.3 < 297.  This test point is out of tolerance.

No direction is given, in the assembly manual, for test points out of of tolerance. 

Any chance this is a component tolerance issue?  One that might be resolved by replacing a component or two?

Thoughts?

Vince
« Last Edit: August 16, 2020, 05:37:03 PM by vince »
Vince Duperron