Lionel Hobby Shop Board Failure

I think you are on the right track and I agree it should be an easier fix than some.  Just out of curiosity, did you confirm power is actually making it to the board?

Yes-

@MartyE posted:

I think you are on the right track and I agree it should be an easier fix than some.  Just out of curiosity, did you confirm power is actually making it to the board?

Yes, there is power going to the board and I have bypassed the switch to ensure that was not the culprit. Verification of both was done on the layout as well as the bench using a different transformer.

I have the Cowens Hobby and the same thing happened to me except the lights worked. The small trains were always a problem. I finally got tired of fixing the circuit board and hooked  the motor to a 5VDC 1.5A adapter with a switch and I have never had a problem since

@ScottM posted:

Yes-

Yes, there is power going to the board and I have bypassed the switch to ensure that was not the culprit. Verification of both was done on the layout as well as the bench using a different transformer.

I'm just going by what I can find, but I think we are talking about the older version of the hobby shop board right? Of that there are 2 types. That said, since nothing gets power- my logical guess is we have a rectifier failure feeding the multiple regulators with DC. I also believe the reason they used multiple regulators was to reduce the current any one regulator was carrying by separating the loads. The likely hood that all of them failed, while possible, IMO is low. So again, since nothing works, I generally start tracing at the power entry to the board, then expected AC to DC rectification, then filtering (capacitance), then regulation to individual loads.

This image from Lionel parts shows a large single diode in the left upper corner and then large capacitor for a half wave rectification.I have no idea if there are components on the backside but appears to be a single sided board and fairly straightforward to reverse engineer.

This slightly newer version of the board appears to have a switching regulator as seen by the inductor and the 8pin DIP chip and possibly a transistor for the switching, and then other linear regulators. That said, the front end rectification being half wave single diode appears to be the same.

Again, I would work my way forward through the board starting at the AC entrance, then check for DC voltage on the large capacitor. From there, try to trace out and follow that voltage. It's possible one the large resistors failed, but also another suspect is that switching regulator.

I've heard that the diode pack is a common failure point, and it's easy to replace with standard silicon diodes.

OK, Looking again, this is one of those diagrams I keep getting wrong even though it's right in front of me.

The common failure diodes are for reducing the motor speed. The power input from the other hydrant is still going directly to the board.

I had to download the PDF diagram instead of looking at it in a web browser sideways.

Again, per the diagram, the diode "string" is in series with the motor to reduce it's speed. That said, if absolutely nothing worked, my guess is that big diode right near the red wires that are the power entrance to the regulator PCB.

The diode string appears to be specifically in series with the motor after the board as an output.

I looked through my stash and found 2 1N007 and 1 1N5400 diodes, all which have a higher rating than the original.  Are there any issues with using these?

Again, now that I finally got a better look at this, if absolutely nothing worked, no lights, no flashing LEDs, no motors, my top suspect is that single large onboard diode that by all accounts, rectifies the bulk AC coming in on the red wires to the PCB. Being half wave, the big bulk 35V rated capacitor is trying to smooth that out before it logically goes through those large sand resistors, and then into the various voltage regulators. The flasher circuit for the crossbucks appears to be the vertical little daughter card most likely with a blob covered chip die. The large resistors are there just to share the heat load and reduce the thermal load of the regulators by spreading the heat between a fixed resistor and the typical 3 pin linear regulator.

@ScottM posted:

I looked through my stash and found 2 1N007 and 1 1N5400 diodes, all which have a higher rating than the original.  Are there any issues with using these?

No issue that I am aware of. The last digit is just the peak reverse voltage, higher numbers= higher voltage rating.

Those are 1A and 3A rated diodes respectively, the 1N4007 is just a very high 700V rated diode.

@Vernon Barry posted:

Again, per the diagram, the diode "string" is in series with the motor to reduce it's speed. That said, if absolutely nothing worked, my guess is that big diode right near the red wires that are the power entrance to the regulator PCB.

I put the test leads across the circled diode and get the same voltage as that coming in.  Multimeter indicates AC, so I'm not sure I am measuring this correctly.

I switched the multimeter from auto to DC and get the same reading (identical to input voltage) even when switching leads.  If I'm not mistaken, shouldn't I get voltage one way and zero voltage when reversed?

Don't measure across the diode for voltage.

Measure across the capacitor for DC voltage.

The white arrow stripe on the capacitor is the negative lead (black), the other lead to the inside the board space is the positive.

Problem Solved!

After some experimenting, the root cause was the string of three diodes in the motor circuit.

I did test replacing the incoming power diode which yielded no results and then turned to the string of three - problem fixed.   Obviously these 3 diodes affect more than just the motor power.

Thank you to all who helped!  You are what makes this forum great.

You can also measure DC at the regulators- both in and out voltages.

In theory, the in voltage is similar to the DC voltage of the bulk capacitor. Output voltage would match the last digit of the regulator marking example 7805= 5V regulator, 7809= 9V, 7812=12V

@ScottM posted:

Problem Solved!

After some experimenting, the root cause was the string of three diodes in the motor circuit.

I did test replacing the incoming power diode which yielded no results and then turned to the string of three - problem fixed.   Obviously these 3 diodes affect more than just the motor power.

Thank you to all who helped!  You are what makes this forum great.

Hmm, interesting. Again, odd that they run the power through the diodes and the motor and the switch (fire hydrant), and that controls other things?

Like I said, I don't have anything other than the provided diagrams, a fair amount of electronic experience, and understanding of components. It's like they are sensing current or voltage through the motor circuit to then turn on the other LEDs?

The part again that threw me- you said nothing worked no lights.
I can understand the motor being on a switch, and maybe the crossbucks and expected that to be on the switch, but not on the switch through more diodes and the motor. Honest opinion- what a screwy circuit.

@ScottM posted:

I have a No. 500 (6-32998) hobby shop that has stopped working. No lights, no motor.  A by-pass to the motor with a 9v battery indicates the motor works properly.  There are no tell-tale signs of failure on the board, but the design seems like it would be simple to repair. Is there a history of a component known to fail? I am ruling out the diodes since all circuits are dead.

Thank you

@Vernon Barry posted:

The part again that threw me- you said nothing worked no lights.
I can understand the motor being on a switch, and maybe the crossbucks and expected that to be on the switch, but not on the switch through more diodes and the motor. Honest opinion- what a screwy circuit.

Upon closer examination, my initial analysis was wrong - the crossbucks do light without the switch being on and without the 3 diodes - I just didn't look close enough and assumed (you know where that leads you ).

In the end, I am happy my $400 accessory is ready to return to the layout.

Glad you got it going.

Nice thread.  Thanks for the discussion.

Yep, it seems those three diodes are frequent failure items.  I suspect that maybe replacing them with beefier diodes might not be a bad move.