DD1 hand controller transistor block replacement

[ErwinvdVelden]

Hi Folks,

Since a few days the declination refuses to move at 0.5x and 1.5x sidereal speed, 8x speed works only at lower power supply voltages. After swapping motors and testing cables I think that the declination transistor block of the DD-1 hand controller partially died, probably because of an extensive excess voltage. Has anyone done this before and does he/she knows what type of replacement chip to get?

I'll remove the cooling fin of the broken one tomorrow, but I'm not sure if the chip type still is readable.

Cheers,

[gbeal]

Hi Erwin.
I am sure some clever dickie out there will know, or be able to help. First guy that springs to mind here is Robby. Try a PM, or if he hasn't awoken in a day or so I will e mail him.
Gary

[Dennis]

Hi Erwin

Try the Vixen group on Yahoo Groups. Here is a copy and paste of post http://groups.yahoo.com/group/Vixen-scopes/message/1467

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Actually, my controller has a reference, inside, of DD1 - MRC and it
has become practically useless because it drives my GP-DX in a
spasmodic fashion.

I suspect it has failed because it has neither over-voltage nor
reverse-polarity protection. Does anyone know of a likely fix?

Speaking to Bev at COAA, the guy who is behind the excellent WinCTC GoTo system, he reckons that the design of the plug and socket can reverse polarity and kill a transistor inside the controller box. He reckons that by replacing transistor type 220 KA7805A he cured his DD1 some time ago. However, my DD1-MRC may be a later model than his and does not incorporate the same transistor. Meanwhile he has gone over to an AWR controller which has the protection and drives much faster than the DD1.

Any one know how to diagnose what has failed and how to cure it, please?

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Cheers

Dennis

PS - You are working it too hard; go to bed and let the poor drive get some rest :-)

[ErwinvdVelden]

Thanks Dennis,

Strangely my hand controller has wrong polarity protection, at
least I connected it the wrong way dozens of times. Also it is only
the DEC, as I understand from that mail it affects both axis. I
read about a similar problem on a German thread (that place
were these mounts come from :lol2: ), but besides sending the
controller to Vixen and waiting for 3 months they didn't know a
solution either.

My experience with electronics is that the hottest components die
first, hence my idea to replace the transistor block, a Toshiba
TA8415P, which is not available in Australia. Bed, is that the
latest observing
chair ??????????????????????????????????? ????????????????????
??????????????????????????????????? ?????????????????????????
??????????????????????????????????? ?????????????????????????
??????? Oops! I'm still awake!

And thanks to Gary for his offer, I'll first try a PM.

Cheers,

[Dennis]

Hi Erwin

Also found this via google:

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I have a GP mount with dual motors and the Vixen DD-1 controller. I noticed that when running the controller from a 12V supply (as is the case when using the 8 D cell holder or running from a 12V lead acid battery or car cable), the RA motor would "stutter" with the controller set to the 32x position.

I found out that the DD-1, when set to 32x, powers the drive motors with whatever voltage the controller is being fed. At 1.5x and 2x, it drives the motors with a regulated (5v) voltage.

The stepper motor controller Vixen uses (Toshiba TA8415P) is rated at a maximum of 400 mA per phase. The motors have 20 ohm windings. So with a +12V supply, the chip was being asked to deliver 150% of it's maximum rated current. Worse, at 12V, the chip is being asked to deliver TWICE its recommended maximum or 300 mA. Vixen claims the controller can use 7.5 - 12 volts, and realistically, many people will want to use a "12" volt lead acid battery or car cable, which is actually closer to 13-14 volts.

In my case, the controller chip was overheating with the higher voltage, and unable to reliably step the motors. Worse, the driver for phase 1 was blown.

So what I did was to wire a 7808 1A voltage regulator into the input. This means that the motors will never be driven with more than 8 volts regardless of the input voltage, and the driver will remain at or below its rating. This will allow me to reliably use a 12V lead acid battery for field power. (regarding the blown output, the Dec drive uses a different chip [Toshiba TD62103, which has a higher rating of 500 mA, although it is also being used beyond specification], and I was able to rewire the bad phase 1 output through this chip to get everything working properly.)

I recommend that anyone with a Vixen DD-1 controller either not use the 32x setting, or only use an 8 volt power source. I got mine second hand, but if you bought your's new, this obvious design flaw is definitely a "defect in material or workmanship," so
demand that Vixen correct the issue under warranty.
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Cheers

Dennis

[ErwinvdVelden]

Hi everyone,

I found the replacement part for the Toshiba TD62103 stepper Darlington sink, it's the Motorola ULN2003 / MC1413 rated @ 500 mA and costed me $1.78 at the local electronic parts store.

I'll put it in tonight and let you know how I went.

Thanks for your help!

Cheers,

[Robby]

Hi Erwin,
I replaced the driver chip in my "old" DMD-3 vixen controller with discrete MOSFETS. Made a "huge" difference.
If you end up with the same problem with the replacement chip let me know & we'll see what we can do!
Cheers

[ErwinvdVelden]

Hi everyone,

I replaced the chip and everything works fine again. Much cheaper than buying a new hand controller and having to modify it again for autoguiding. To relieve the hand controller a bit I'll use an 9 V battery from now on.

Robbie, you were talking about a discrete MOSFET controller, what is the part number?

Cheers,