Scumacher 1042A-PE battery charger has no output.

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

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.

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.

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.

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?

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.

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:

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

The other is an LM2903 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?

Thanks for your reply.

David Farber wrote: ==============

... phil

Thanks Phil.

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?

1. 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?

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

Thanks for your reply.

David Farber wrote: =============

** Good.

** It can be much higher as the resistor is in parallel with the device gate and cathode. ** The SCR will do that when it triggers on - if it is working.

..... Phil

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?

Thanks for your reply.

David Farber wrote: ================

** Read my first post again.

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

..... Phil

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.

Are we on the same page now? :-)

Thanks for your reply.

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.

Thanks for your reply.

** Yep - expected that.

The only

** 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 and tested one of the amps as described here:

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.

Thanks for your reply.

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

** What op-amp?

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

> and tested one of the amps as described here:

** Irrelevant. ** Normal for comparators.

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

...... Phil

I missed that point. I will reconfigure my test circuit and report back...

Thanks for your reply.