Scumacher 1042A-PE battery charger has no output.

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David Farber

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Aug 19, 2022, 10:39:05 PMAug 19
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This Schumacher 1042A-PE battery charger stopped functioning today. It
seemed to work for a little while but when I noticed the car battery's
voltage wasn't slowly increasing after performing a 2 amp charge for 2
hours, I checked the voltage at the charger's cables and it was 0 volts.
The continuity of the switches and cables were all good. I did find a
power semiconductor which I could not identify, BTW70-200SN. I looked in
an old ECG cross-reference book and the closest match was for a
BTW69-800 which is an SCR in a TO-218 package. The package seems to
match the device I'm looking for. I made some measurements with my
Simpson 464 DVM on the 2k ohm scale. Pins 1 and 3 measure 38 ohms
regardless of test lead polarity. All other combinations of continuity
measure open circuit. In circuit, pins 1 and 2 are soldered together.
Any idea what this component is or how to test it?

Thanks for your reply.

David Farber
Los Osos, CA

Phil Allison

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Aug 20, 2022, 12:08:38 AMAug 20
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David Farber wrote:
=============
** Could be an SCR maybe.............

With a 1A, current limited, DC supply of about 12 V, + on the anode - on the cathode, apply a brief pulse of +50mA at +1.5V to the gate with - on the cathode as well. The 12 volt supply should the be clamped at about +1.2V.
You 38 ohm readings are normal.


..... Phil




Jeff Liebermann

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Aug 20, 2022, 1:25:38 AMAug 20
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On Fri, 19 Aug 2022 19:39:03 -0700, David Farber
<farberbe...@aol.com> wrote:

>This Schumacher 1042A-PE battery charger...

Are you sure about that model number? Methinks that SE-1052A-PE is
more likely.


--
Jeff Liebermann je...@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

David Farber

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Aug 20, 2022, 2:30:30 AMAug 20
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On 8/19/2022 10:25 PM, Jeff Liebermann wrote:
> On Fri, 19 Aug 2022 19:39:03 -0700, David Farber
> <farberbe...@aol.com> wrote:
>
>> This Schumacher 1042A-PE battery charger...
>
> Are you sure about that model number? Methinks that SE-1052A-PE is
> more likely.
>
>
Youthinks correctly! It is a 1052A.

Thanks for your reply.
--

Jeff Liebermann

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Aug 20, 2022, 3:09:35 AMAug 20
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On Fri, 19 Aug 2022 23:30:27 -0700, David Farber
<farberbe...@aol.com> wrote:

>On 8/19/2022 10:25 PM, Jeff Liebermann wrote:
>> On Fri, 19 Aug 2022 19:39:03 -0700, David Farber
>> <farberbe...@aol.com> wrote:
>>
>>> This Schumacher 1042A-PE battery charger...
>>
>> Are you sure about that model number? Methinks that SE-1052A-PE is
>> more likely.

>Youthinks correctly! It is a 1052A.

Unfortunately, that didn't help when looking for information using
Google search. I couldn't find anything on the SE-1052A-PE except the
owners manual. No schematics or articles on repairing it. No photos
of the inside.
<http://powertool.manualsonline.com/manuals/mfg/schumacher/se_1012d_se_1052.html>
Notice that the user manual covers a range of models which probably
share similar circuitry. Try searching for the other models.
SE-1010-2, SE-1012D, SE-1052, SE-1250

Jeff Liebermann

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Aug 20, 2022, 3:28:18 AMAug 20
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On Sat, 20 Aug 2022 00:09:28 -0700, Jeff Liebermann <je...@cruzio.com>
wrote:

>On Fri, 19 Aug 2022 23:30:27 -0700, David Farber
><farberbe...@aol.com> wrote:
>
>>On 8/19/2022 10:25 PM, Jeff Liebermann wrote:
>>> On Fri, 19 Aug 2022 19:39:03 -0700, David Farber
>>> <farberbe...@aol.com> wrote:
>>>
>>>> This Schumacher 1042A-PE battery charger...
>>>
>>> Are you sure about that model number? Methinks that SE-1052A-PE is
>>> more likely.

>>Youthinks correctly! It is a 1052A.

>Unfortunately, that didn't help when looking for information using
>Google search. I couldn't find anything on the SE-1052A-PE except the
>owners manual. No schematics or articles on repairing it. No photos
>of the inside.
><http://powertool.manualsonline.com/manuals/mfg/schumacher/se_1012d_se_1052.html>
>Notice that the user manual covers a range of models which probably
>share similar circuitry. Try searching for the other models.
>SE-1010-2, SE-1012D, SE-1052, SE-1250

Bingo, except that there's no SCR in the schematic.
<https://www.fixya.com/support/t25414948-wiring_diagram_switch_se_1052>
<https://www.fixya.com/support/t7882270-looking_wirring_diagram>
Kinda looks like just the PCB wiring and not the complete unit. This
is from a different charger (SE-1275A) that MIGHT have the same
wiring. How close are the drawing and schematic to what you have?

David Farber

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Aug 20, 2022, 11:38:29 AMAug 20
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Hi Phil,

Looks like I have to make another correction. Jeff pointed out the model
number I posted was wrong, the correct model is 1052A-PE

The other correction is that pins 1 and 2 of the "SCR" are NOT soldered
together on the pc board. Pin 2 (center pin) is snipped off and the
connection is made through the component's heat sink. This is the same
heat sink which is electrically common to one end of four discreet
(bridge?) diodes.

Getting back to the testing of the SCR (if it is an SCR), how do I
identify anode, cathode, and gate?

Thanks for your reply.
--

David Farber

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Aug 20, 2022, 3:41:26 PMAug 20
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Hi Jeff,

Regarding the model number, I don't see any indication of the SE prefix
before the 1052A-PE.

Here is a photo of the pc board:

https://app.box.com/s/0bjg0nafgy74e9wo0qyo689uaux0znnc

I don't see much similarity between this unit and the partial schematic
you linked.. Let me explain the basic layout from following a few wires
around the device.

One end of the AC cord goes to the primary of the transformer. The other
end goes to the center terminal of the DPST Charge/Engine-Start rocker
switch. From there the wires interconnect with the DPST 2 AMP/10 AMP
rocker switch. The net result is that different primary wires are used
depending on how those two rocker switches are positioned.

The pc board layout has two IC's. One is an LM2901
https://www.st.com/resource/en/datasheet/lm2901.pdf

The other is an LM2903
https://www.st.com/resource/en/datasheet/lm2903.pdf

I confirmed that both IC's have 12V going to their respective VCC terminals.

There are four, heat sinked diodes (bridge?) that connect from the
transformer secondary. The diodes share a common terminal with pin 2 of
the SCR(?)

There are no LED's or power-on light. The only indicator on the panel is
the ammeter.

I hope that helps give you a general idea of the circuit. As I remember,
the battery cables will still show 12V even when there is no load. Does
that sound correct?

Phil Allison

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Aug 20, 2022, 6:52:35 PMAug 20
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David Farber wrote:
==============
>
> Getting back to the testing of the SCR (if it is an SCR), how do I
> identify anode, cathode, and gate?

https://au.mouser.com/datasheet/2/389/sgsts33425_1-2282554.pdf


... phil

David Farber

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Aug 20, 2022, 8:50:28 PMAug 20
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Thanks Phil.

David Farber

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Aug 21, 2022, 2:22:53 PMAug 21
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On 8/19/2022 9:08 PM, Phil Allison wrote:
Questions about the test setup:

1. For my 1A, current limited, DC supply, I was going to using my bench
power supply and set the current limiter to 1A but doesn't there need to
be a resistor in series with the power supply in order to prevent the
current limiter from tripping?

2. For the brief pulse, I was going to use a 1.5 volt, AAA battery.
Since there's a 38 ohm (internal resistor?) connection between the
cathode and gate, does that mean the 1.5 V pulse will be automatically
limited to about 40mA?

3. How do I clamp the 12V supply to +1.2 volts?

Thanks for your reply.
--

Phil Allison

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Aug 21, 2022, 9:22:28 PMAug 21
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David Farber wrote:
=============
>
> Questions about the test setup:
>
> 1. For my 1A, current limited, DC supply, I was going to using my bench
> power supply and set the current limiter to 1A

** Good.


> 2. For the brief pulse, I was going to use a 1.5 volt, AAA battery.
> Since there's a 38 ohm (internal resistor?) connection between the
> cathode and gate, does that mean the 1.5 V pulse will be automatically
> limited to about 40mA?

** It can be much higher as the resistor is in parallel with the device gate and cathode.

> 3. How do I clamp the 12V supply to +1.2 volts?

** The SCR will do that when it triggers on - if it is working.


..... Phil





David Farber

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Aug 21, 2022, 11:43:04 PMAug 21
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Assuming the SCR is working and it's clamping properly, where am I to
measure the 1.2 volts? The anode is connected directly to the 12 V
supply and the cathode is grounded. That leaves the gate. Will it
measure 1.2 V after I remove the 1.5 V supply?

Phil Allison

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Aug 22, 2022, 12:28:09 AMAug 22
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David Farber wrote:
================
> > ** It can be much higher as the resistor is in parallel with the device gate and cathode.
> >
> >> 3. How do I clamp the 12V supply to +1.2 volts?
> >
> > ** The SCR will do that when it triggers on - if it is working.
> >
> >
> >
> Assuming the SCR is working and it's clamping properly, where am I to
> measure the 1.2 volts? The anode is connected directly to the 12 V
> supply and the cathode is grounded. That leaves the gate. Will it
> measure 1.2 V after I remove the 1.5 V supply?

** Read my first post again.

SCRs, once triggered, conduct large currents with small voltage drops.


..... Phil

David Farber

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Aug 22, 2022, 12:10:36 PMAug 22
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Here's what I am seeing:

+12 V ---> Anode---> grounded Cathode --> return to power supply -V

When the gate triggers the device into forward conduction mode, the
current flows but without some type of load in series with the circuit,
it will immediately trigger the current limiter. And now I think I've
had my, "Aha!" moment. My B&K 1601 bench power supply can limit the
current to 1A but it doesn't actually limit the current in the fashion I
think you intended. It simply turns off the power and the overload light
comes on. I think you meant a light bulb type of limiter where current
can continue to flow but not above 1A.

Image of my B&K 1601.
https://cdn8.bigcommerce.com/s-a1x7hg2jgk/images/stencil/1280x1280/products/37485/195211/bk-precison-model-1601-regulated-dc-power-supply-105-125v-ac-60hz-160w-as-is-1.40__72743.1490286610.jpg

Are we on the same page now? :-)

David Farber

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Aug 24, 2022, 8:34:18 PMAug 24
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On 8/21/2022 9:28 PM, Phil Allison wrote:
Finally got around to testing the SCR and it works perfectly. The only
other active components other than the power supply diodes are the two
IC's, LM2901 and LM2903.

Phil Allison

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Aug 24, 2022, 10:00:19 PMAug 24
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David Farber wrote:
>Phil Allison wrote:
> >
> > ** Read my first post again.
> >
> > SCRs, once triggered, conduct large currents with small voltage drops.
> >
>
> Finally got around to testing the SCR and it works perfectly.

** Yep - expected that.

The only
> other active components other than the power supply diodes are the two
> IC's, LM2901 and LM2903.
>

** I see a TO92 pak transistor near the SCR.
Lotta resistors about too.
Dead easy to check them for opens.

.... Phil


David Farber

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Aug 26, 2022, 7:14:12 PMAug 26
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I removed the 8-pin DIP op amp and tested one of the amps as described here:
https://www.circuitbread.com/ee-faq/what-are-the-golden-rules-of-op-amps
I used the schematic at the very bottom of the page as the test setup.

The result of the test was that the non-inverting input voltage (4.5V)
did not match the inverting voltage input (0.7V) and according to one of
the golden rules of op amps:

"In a circuit with negative feedback, the potential difference between
the inverting and non-inverting inputs is zero...."

That means the op amp is defective.

By the way, many of the voltage +/- inputs for the quad and dual op amps
when measured in-circuit were amiss. In other words, the non-inverting
input voltages were not equal to the inverting voltages but perhaps
there was no feedback loop? (too many pc traces for me to keep track of.)

In summary, I'm going to replace both chips. I think I checked every
semiconductor, resistor and capacitor on the board and I'm fairly
confident that my diagnosis is correct.

Phil Allison

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Aug 26, 2022, 7:52:52 PMAug 26
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David Farber wrote:

=================

> >
> > The only
> >> other active components other than the power supply diodes are the two
> >> IC's, LM2901 and LM2903.
> >>
> >
> > ** I see a TO92 pak transistor near the SCR.
> > Lotta resistors about too.
> > Dead easy to check them for opens.
> >
> > .... Phil
> >
> >
> I removed the 8-pin DIP op amp

** What op-amp?

FYI the LM2903 is a *comparator* so is the LM2901.

https://www.st.com/resource/en/datasheet/lm2903.pdf

> and tested one of the amps as described here:

** Irrelevant.

> By the way, many of the voltage +/- inputs for the quad and dual op amps
> when measured in-circuit were amiss.

** Normal for comparators.

Your circuit is * non linear * and uses switching to control the SCR and hence output of the charger.


...... Phil

David Farber

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Aug 26, 2022, 11:39:21 PMAug 26
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I missed that point. I will reconfigure my test circuit and report back...
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