Can variable channel to start at less than 5 volts?

Using DCS 4.30 you can start at 1 volt.

A very worthwhile addition to the capability I might add.

I see ... what's the level of risk involved when updating the firmware from 4.20 ?

That's a debatable issue, yamawho. 

I assume you want to have a lower voltage because you run conventional and can't slow locos enough.  Cause is that the TIU alters the wave form, and the alteration becomes greater the more it has to drop voltage.  Reducing the input voltage to the TIU will help considerably.

Conventional locos with Pullmore motors run good starting at 5V but newer ones with DC motors start too fast. So if I use a Lionel 1033 90 transformer and don't turn it all the way up, I would get better slow speed control?

That's correct.  To illustrate, I have an MTH Docksider.  If I feed 5 volts (per the remote readout) to it, while inputting 22 volts into VARIABLE IN, it flies.  If I drop the input to, say 14 volts or so, it runs more normally.  Try it with your 1033.  Play with the input voltage and see how different settings react.

Of course, when inputting less that 22 volts, the voltage reading on the remote is not accurate, but that doesn't matter.

If you operate in normal, rather than Super, TIU mode, go ahead and upgrade. The only two "major" bugs are in Super TIU mode only. Further, both of them are rather rare.

I tried using a 1033 and my loco would not run right no matter what the voltage I set.

What problems did you encounter and how do you have the transformer, TIU, & track wired?  You should use a wall wart connected to the AUX power input, so that the TIU has an adequate power supply regardless of the voltage you apply.  But applying 12 volts or over to FIXED 1, even without a wall wart, should work.

I tried wiring the 1033 U to red and A to black on Var 2.

I still left Fixed 1 wired to a powermax 180 watt to power the dcs track along with powering the TIU.

The way it works at present is I jumped the power from Fixed 1 to Var 2 and it's working but as I said before starts at 5V minimu.  

Be sure you have the two transformers properly phased.  If both (1) they are phased and (2) the powermax is properly connected, 1033 "U" should go to black and A to red.  When you say it starts at 5-volt, are you getting that reading from the remote?  If so, it is not accurate when less than 22 volts is applied.  Also, even though you may get a similar reading on a voltmeter, the wave form differs.

Here's a suggestion.  Disconnect both wires from the OUTPUT of FIXED 1, but leave power applied to the INPUT.  Try the loco on VAR 1

Isn't the 'U' post a "common" post (as opposed to "hot"), meaning it should be hooked to the black terminal on the TIU?

---PCJ

MTH advises to wire the U on the 1033 to the red post.

Digging out old MTH papers, I find you are correct, yamawho, about U to red.

Have you tried my suggestion?  Do not jumper the inputs.

Why go to all the trouble of fooling with the 1033 when you can just load 4.30 and have variable voltage down to 1 volt?

I don't know ... FEAR 

There can be a fine line between fear and wisdom/prudence.  In fact, sometimes it is prudent to be fearful.

Personally, I would not upgrade to 4.30 at this time to solve the problem yamawho is facing, but would attack it in the manner I mentioned above---reducing input voltage for conventional operation---which I do on those rare occasions when I want to run conventional.  Others may and, I'm sure, do differ.

Plenty of people, including me, have upgraded to 4.30 and are enjoying the new features offered.  I've experienced no problems with the upgrade. The only things that have been mentioned are some minor issues with MU configurations, but I believe there were some issues with MU operation with 4.20, so I view that as a wash.

Since that would allow the desired operation without changing anything about the hardware configuration, we'll just have to agree to disagree on this point.

Sometimes it's not prudent to be fearful.

I have Barry's book but I'm on the road.

Do I need special cables etc if I bite the bullet and try it?

With the transformer or upgrading the firmware?

Upgrading the firmware ...

You need: a 1/8" stereo cable to connect two terminals on the TIU for upgrading the TIU; a telephone handset (not wall to phone) cord to connect remote and TIU; a serial cable to connect computer to TIU.  If your computer does not have a serial port, you would need a USB to serial adapter cable (available at Radio Shack, but if your TIU is Rev L, you can use a USB cable.  These are all readily available.

OK ... using 1033 U to red and black to A, I inverted the plug to the wall this time and it works 

I tried it with the 1033 at max ... voltage reading is15v and it works much better, no more jump starts.

I will try this out for a while to see how it pans out.