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Re: [ATM] My Mototrak V stopped working... what will I do?
Thank you so much for your quick replies! I have a hunch you all have
shared that feeling in the pit of your stomach while under a clear sky.
The good news is I got it working. My problem was that I needed to replace
both the transistor that was getting warm and the one that was not.
However, now they are both getting pretty warm, warm enough to make the
electrical tape they are wrapped in gooey. They are also getting warm
without a load. I am hoping they were the problem and not just one of the
casualties.
I don't think it was the drive because I have a second drive and it wasn't
working on that one either before I fixed it. Also, I've been using this
setup for about two years now without a problem.
I am not seeing any transformers at all. I do see one inductor (only two
leads instead of four right?) About the buzzing, it doesn't seem fast
enough to be 60 Hz. It's sharper too than like the hum from a flourescent
light. I could also make it stop too while I had the thing apart by
touching one of the transistors while I was seeing if it was hot (I may have
been shorting a circuit).
Something that I have noticed is that the AC adapter is putting out 17V,
contrary to its 12V label, and it does have the amps to back it up, 5A,
contrary to the 800mA on the label. I am wondering if the Mototrak is
getting fed too much juice, is putting out too much juice, and the
transistors are the weak link in the chain.
Before I fixed the transistors, the output voltage was 100V AC. Now it is
600V AC! I do have an independent AC adapter that does output the correct
12V DC. When it is connected to that, it outputs 80V AC. However, the
transistors still get warm under no load.
I am just feeling that the problem is the transistors. There are actually
four altogether, two matched pairs: IRFF9120 and 2N6790. I replaced the two
IRFF9120 but I left the 2N6790.
I bet the reason they came out with the 10W model later was because of this
problem and I bet all they did was beef up the transistors to be able to
take more amps. I am thinking these transistors are what they are using to
amplify the signal from one of the smart parts of the circuit and that the
over voltage from my power supply is only exacerbating the problem.
If I am right, I would like to replace the transistors with ones that can
take the extra amps without changing the properties of the circuit. I found
this handy website that specs my existing transistors:
http://www.chipcatalog.com/IR/IRFF9120.htm. Unfortunately that's over my
head and I don't know how to pick out a component that can take the amps.
Am I looking for the same specs but with a higher power dissipation?
Any suggestions on how to validate my gut feeling about the transistors,
pinpointing them as the cause and not a side effect?
>From: Ken Hunter <atm_ken_hunter@yahoo.com>
>To: Christopher Dalla Piazza <dalchri@hotmail.com>, atm@atmlist.net
>Subject: Re: [ATM] My Mototrak V stopped working... what will I do?
>Date: Wed, 18 Oct 2006 19:04:44 -0700 (PDT)
>
>First off... I'd suspect the transistors are not making the noise. More
>likely a step-up transformer inside the unit is making the noise. It's
>possible that the transformer has developed a shorted winding. If that' the
>case, the transformer must be replaced. It could also be that the mount has
>developed a "sticky" drive which requires more horsepower to move the
>mount.Fortunately the transformer is usually a simple filament transformer
>run backwards to generate the operating voltage for a synchronous motor.
>The transistors are not so special either... the trick is to determine
>which is the problem.
>
> First thing I would do is unplug the mount and let the unit idle for a
>while then check the temperature of the unit without the load. It should
>run cool without a load and not make strange noises. If it fails this test,
>there is something wrong inside the unit and we can go from there.
>
> If it passes this test, check the mount for binding. You want to be able
>to move the mount very easily by turning the shaft that the motor drives.
>You may have to remove the motor to make this test... That's OK, as you can
>then reconnect the motor and run the unit without a load on the motor. It
>should make slightly more noise and get slightly warmer but not by very
>much.
>
> This should get you started.
>
> Ken Hunter
>
>
>
>
>Christopher Dalla Piazza <dalchri@hotmail.com> wrote:
> I'd hoped that it would last forever but...
>
>It does not appear to be producing enough power to start my RA drive
>anymore. I have noticed that two of the transistors are getting very hot.
>These transistors were pointed out to me earlier by JMI in determining if I
>had the 5W or 10W model. Because these transistors were small, I had the 5W
>model.
>
>The drive corrector also emits a buzzing sound that increases/decreases
>with
>the frequency of the current as I press the east/west buttons. It's hard to
>isolate but it seems to be coming from the transistors. It has been making
>that noise for awhile and I can't be sure that it hasn't always made that
>noise.
>
>I am praying that the problem is one of the simple components and not any
>of
>the smarts that is built into it.
>
>The reason I am so set on fixing it is because I don't know where to get a
>drive corrector anymore!! My mount is not integrated with a corrector. All
>I need is E-W AC, and N-S DC control with an autoguider input. No one seems
>to sell one. So, faced with having to possibly build a replacement, it
>can't be harder to fix what I have.
>
>Does anyone have any ideas? I am completely dead in the water for imaging
>until I find a solution. Any pointers to products I don't know about or
>basic electronics troubleshooting would be greatly appreciated!
>
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