MAJOR Dew Problems - Broken Controller or Heaters?

[Logieberra (Logan)]

Hey guys

I continue to get dew and frost on my scope down here in Canberra. I can't figure out what I'm doing wrong, and it's really annoying

Ok, so here's my equipment:

1. used Kendrick Model VI Dew Remover (purchased on here in the last month)

2. homemade dew heaters (followed these instructions perfectly, and I can solder very well! Omaroo's instructions at: http://www.myastrospace.com/DIY_Dew_Heater.htm)

I have been testing the setup the last few nights and I have run the unit on the lowest and highest settings. It does nothing.

When I touch the dew heater straps they are the same temp. as the scopes. By comparison, I tested the unit side by side with a friend's setup (Tak66 on here), and you could detect the slightest warmth on his straps. Something is wrong here...

I have tested the Kendrick on the voltmeter and it provides just shy of 12v on both low and high settings. The voltage seems constant. I took the unit apart when I first received it to checki it's internals. It looks like one end of the circuit board is brown / has gotten hot under this little square metal thing, but I thought nothing of it given the unit is not new.

Please help guys, I would like instructions on how to test the unit and heaters to see what's happening.

[Bassnut (Fred)]

Are you testing the output voltage with the straps pluged in?. If not, do that.

Whats the resistance (ohms on your meter) of the straps with them not plugged in?.

[wasyoungonce (Brendan)]

A pic of the internal cct board would help but apart from that..what Fred said:

[Logieberra (Logan)]

Thanks guys, will test soon and take a shot of the board.

1. Will test the output voltage with straps plugged into the Kendrick (will put the meter's (+) and (-) rods on the end of the heater's parallel wires that I made.

2. Will test the resistence of the heaters, same method above, but not plugged into the Kendrick.

Back soon!

Thx guys.

[thunderchildobs]

Hi Logan

My understanding of the kedrick is that that is voltage is turned on / off for a period time. A low settings turns off the current for a short period of time, a high setting has power on all / most of the time. Using a volt meter should show you when power is being applied.

Also check the connectors on the side of kendrick to see if the voltage is reaching the heaters.



Brendan

[Logieberra (Logan)]

Ok, so here are the pics and test I just ran:

http://www.flickr.com/photos/4928648...7624147154851/

The pic shows the brown spot I mentioned above.

1. voltage test, nothing connected, just the kendrick outputs (x4): 12.9v constant.

2. cable connected, with connector for kendrick output, end of cable 12.9v constant (same test as above, just with the cable I am using to be sure)

3. homemade heaters connected to Kendrick, checked the voltage just before where the heater begins. Under voltage it reads 0.65v constant (regardless of where I put the Kendrick dial)

4. checked a buddies heater connected to Kendrick, designer brand, checked voltage before where the heater begins. Under voltage it reads 1.9v constant (regardless of where I put the Kendrick dial)

5. tested my buddies heater and unit (his plugs directly into the 12v, no controller, just heater straps and cig adapter, 12.8v constant (this explains why his get warmsh vs. mine which does nothing)

The red light is on constantly when turned on, and I am unable to adjust the voltage of the unit regarldes of where the dial is positioned...

Thanks guys

[erick (Eric)]

Logan

Read my thread on the Kendrick.

http://www.iceinspace.com.au/forum/s...ad.php?t=57962

I'm not impressed by them, but I got the one I have working. The 555 IC had blown up in mine - sounds like you have the same problem. That resulted in max volts out at all settings of the control knob.

So your heaters should have been running flat out and quite warm to touch, if yours is behaving that way.

Woops! I just looked at your photo. Brown is under the driver transister/FET. Must have been overheating? But I would still suspect the 555 (as well?)

Have you checked the resistances of your heaters? Have they "blown"?

[Logieberra (Logan)]

Erick

I have had this unit for one month, if that. It was purchased used from Breanda (Thunderchilddobs).

In the first few times that I tested it out I only ran it on a low setting (as per advice from Humayun down here in Canberra, as I heard it runs the batteries flat otherwise, or can cause the air around the scope to bubble). It was hard to tell if it was working or not as there was a slight breeze which helped the dew situation. We had a big frost this week and that's when I realised she's stuffed.

I'm a fiddler, so when the unit arrived I opened her up to clean out the dust and inspect and I saw the brown spot, but assumed it would be ok b/c the unit does produce heat, and it's used. Turns out I was wrong...

I have never felt any warmth from any heater what so ever. It was shipped to me as it currently is....

[erick (Eric)]

If you are handy with a soldering iron and have Jaycar nearby, I suspect it will be fairly easily fixed. This is the third Kendrick VI that I have heard had a problem in the circuit.

There is enough info in the thread I listed (thanks to all the friendly tech-heads who couldn't resist drawing up the circuit and troubleshooting it!) to solve your problem with the controller.

But I would be checking that all your heaters are in good shape still.

I just touch my lips to the outside of my dewnot heaters. If slightly warm to my lips, all is fine.

[Bassnut (Fred)]

Its no big deal, the lack of voltage underload tells me the fet is blown, no load voltage is irrelavent.

If you can read the fet type number, a new one will be a $ or so, and since you can solder well, its an easy fix. In fact just about any power fet will do. Dont freak out, its a minor set back.

[adman (Adam)]

i would imagine that if it got hot enough to basically cook the PCB, then the FET is not going to be much good to anyone any more....thinking about it, maybe it is the heat from the slowly cooking FET that keeps the dew at bay in these Kendricks??

[wasyoungonce (Brendan)]

a circuit is here...I think it's the same type.

[Bassnut (Fred)]

Oh yeah , so whats Q1 then (part no) .

[wasyoungonce (Brendan)]

Q1 is something that lets smoke out.

Otherwise its an IRFZ34N 'N' channel mosfet.

Just checked the data sheets...Should be able to use an IRF540N from Jaycar.

Got time on my hands...clouds have rolled in!

[Bassnut (Fred)]

So there you go Logan, get the smoke back in, or buy your self another one from Jaycar, easy as .

[erick (Eric)]

and buy a 555 IC and a socket to suit while you are there, just in case.....

[Logieberra (Logan)]

Guys, great info, and a big help .

The seller (Brendan) has offered a gentleman's solution, and has decided to refund the full amount. Thanks Brendan.

Looks like I will save my pennies for a new Kendrick or equivalent.

Case closed.

Logan