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Old Jul 05, 2011, 11:34 AM
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Powell River BC Canada
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Help identifying an old Heathkit radio/ basket case

I took this radio apart a year or two ago to install new batteries. I got as far as putting new batteries in the little cases then got side tracked. Now I can't remember for sure how to wire the batteries up.

The decal on the back panel can not be read anymore. But it is a Heathkit 8 channel SS on 27 mhz. One of the dual channel type. I'm trying to figure out what model it is. The circuit board part numbers are all 85-xxxx. So is it a GDA-85?
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Old Oct 25, 2011, 02:28 PM
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Canada, ON, Woodstock
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HeathKit Single Stick Radio

Hi Oilman2,

I have just finished getting a Heathkit SS radio up and running for a friend.

The manual calls it a GDA-405-S.

I have another one that I can not get going because I can not locate a source for the integrated circuit in the middle of the encoder board (the board with the blue pots).

If you need any other information, please let me know and I may be able to help.

Fly4Fun,

Wayne Miller
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Last edited by Wayne Miller; Oct 25, 2011 at 10:40 PM. Reason: Spelling mistake
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Old Oct 25, 2011, 08:38 PM
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Powell River BC Canada
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Hi Wayne. I had forgoten about this thread.

Since posting I just recently bought anouther GDA-405-S (and a few other Heaths) and just the other day recieved a GDA-405-S construction manual.

So yes the original radio in the post seems to be a 405-S. The 27 mhz above is not working properly. When you move the stick two servos move. Maybe there is a mixing function? I doubt it. I'm hoping to get batteries in the 72 mhz tonight. If my head ache does not turn into a migrain.

Any way to find a schematic for the Encoder IC? Its not in the manual is it? I'll have to have a look.
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Old Oct 25, 2011, 10:38 PM
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Hi Oilman2,

The schematic in the manual only shows the input and output of the chip (same as the picture I posted), with no internal functions shown. However, I'm still looking up 16 pin encoder/decoder chips in hopes I'll find a modern chip that uses the same pinouts that may work - I haven't found one yet.

Chances are your problem is on the encoder board.

I do have some transistors, diodes etc for the HeathKit SS and if you need any components, check with me and I may be able to help.

You may want to consider picking up an inexpensive newer 72Mhz or 2.4 radio and installing the electronics into the HeathKit SS case - it would be a fun project.

Fly4Fun,

Wayne
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Old Oct 26, 2011, 12:39 AM
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My skill set is pretty much limited to installing new batteries :-)

Have you noticed some of the pots on your heathkits bieng siezed? I've come across quite a few. Penitrating oil and patients seems to be the cure.
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Old Oct 26, 2011, 05:11 AM
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There's a thread in the DIY Electronics forum about the resurgence of Heathkit and there's a reference to manuals still being available for their original kits, for a price.
Follow the link in post #39...

http://www.rcgroups.com/forums/showt...1506894&page=3

A.
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Old Oct 26, 2011, 09:29 AM
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Hi,

I thought I posted a picture of the IC, but I did not. The HeathKit part number is 443-52 and the generic part they quote is SCUS0127, but I can not find the part. I've tried all the web searches I can think of. Any of the HeathKit Xref charts I can find list the same above part.

The schematic is below and is best seen enlarged, right click with mouse and printed off.

Fly4Fun,

Wayne
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Old Oct 26, 2011, 12:02 PM
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It doesn't look like a standard logic IC. I suspect it was a purpose made chip as it seems to do both encoding and decoding of the PPM signal. Very likely to be obsolete now.
It may be easier to replace the whole board with a microcontroller.

Is there a date on the drawing?

A.
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Old Oct 26, 2011, 12:10 PM
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The encoder/decoder chip? Have you tried comparing the pinout to an NE5044 (tx) and NE5045 (rx)?

Andy
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Old Oct 26, 2011, 12:33 PM
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Hi,

There is no date on the print, but the manual it comes from is dated 1972.

I took a look at both of the suggested chips above. On the HeathKit chip, the pins 9 through 16 are outputs, not inputs so the NE5044 won't work, the NE5045 pinouts are not correct.

Thanks for your help, I'll keep looking, if you have any other suggestions, please let me know.

Fly4Fun,

Wayne
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Old Oct 26, 2011, 05:37 PM
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Quote:
Originally Posted by AndyKunz View Post
The encoder/decoder chip? Have you tried comparing the pinout to an NE5044 (tx) and NE5045 (rx)?

Andy
It appears to be the same IC that does both functions rather than one of a pair.

A.
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Old Oct 26, 2011, 05:44 PM
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Quote:
Originally Posted by Wayne Miller View Post
Hi,

There is no date on the print, but the manual it comes from is dated 1972.

I took a look at both of the suggested chips above. On the HeathKit chip, the pins 9 through 16 are outputs, not inputs so the NE5044 won't work, the NE5045 pinouts are not correct.

Thanks for your help, I'll keep looking, if you have any other suggestions, please let me know.

Fly4Fun,

Wayne
Wayne,

It looks as if pins 9 to 16 are connected to the labeled connections from each control pot so it looks like they are inputs at least in this circuit.

Andy.
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Old Oct 26, 2011, 09:13 PM
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Hi Andy,

I have the circuit description (1 page) and theory of operation (2 pages). I have scanned them in along with a rescan of the print, hopefully it is clearer. They are attached. If they are not clear when you download them, PM me with your email address and I'll send them to you direct.

This should give you the function of the chip and how it works.

Thanks for taking the time to look at this for me. Don't spend too much time on it, I appreciate what you have done already.

Thanks for your help.

Fly4Fun,

Wayne
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Old Oct 26, 2011, 09:29 PM
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Powell River BC Canada
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@Wayne. I don't know much about electronics. So don't take the following the wrong way. How did you come to the decision that the encoder ic was at fault. Process of elimination? I would thought an IC would be one of the more long lived parts on the board. As compared to say capacitors etc.
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Old Oct 29, 2011, 12:48 AM
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Hi Oilman2,

Sorry to be so long in getting back to you. I have a scope and I know the the chip is getting the input signal, but does not step through the channels. I put a chip in from another board (has a different problem) and it works fine. So, I'm now looking for a replacement chip for the other board to start troubleshooting it.

Hope this helps.

Fly4Fun,

Wayne
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