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 Post subject: Hurting for help and advice
PostPosted: Feb Thu 08, 2018 7:28 pm 
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Location: Cody,Wyoming,USA
I have a Icom IC-IC-756 Pro III transceiver that has a bad back light inverter transformer. It appears to have a open secondary. The transformer is no longer in production and have spent a great deal of time searching for one and finding out there are several others in the same place I am. It is made by Toyo part number D818HN-1107 a 9 DC volt to 1200 VAC. Even though it appears open for some reason it will allow me a very dim CFR back light and I have found By using a solder iron to heat the molded transformer surface the the lamp comes back up to max output in two steps. I don't have a hi Z HV probe so trying to measure the AC output kills the output. If I can find it I believe I have a RF probe for my meter and was wondering if that would probably also kill the AC also. I now have the transformer removed from the board and cannot even see the size of the wire as it in connected to the terminals under the epoxy. Anyone have ANY ideas of anything that I can try or look for. I don't know if I could possibly find a transformer from a computer inverter or TV. The chances of cutting into the unit and attempting to repair or rewind seems pretty remote.
Joe
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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Thu 08, 2018 7:57 pm 
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Location: Mountains of Mourne. Ireland.
It's TOKO...
https://www.google.co.uk/search?q=Toko+ ... arch&dcr=0

Greg.


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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Thu 08, 2018 8:26 pm 
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Location: Cody,Wyoming,USA
Tnx Greg I have already searched every ToYo site and they all state it is no longer available. I have Googled every place and tracked every bunny trail I could find, The last one I could find that was sold was a Australian site and it was the last one yhey had.
Joe


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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Thu 08, 2018 8:43 pm 
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Yes I saw the Aussie one Joe.

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If your TFT display is...
TFD50W40-MMA
Image
Toshiba TFD50W40MMA LCD panel
ebay $195 ←open to offers... :)
https://www.ebay.com/sch/i.html?_from=R ... 2&_sacat=0

I'm afraid I'm not up in the world of itsy-bitsy Inverter transformers, and... a Yaesu man to boot. hihi
73 de Greg.


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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Thu 08, 2018 8:57 pm 
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I saw no prospects for a replacement transformer after searching around. I also found the guy in Australia who happened to snag a 1-of-a-kind in stock original part to get his radio running.

Have you considered the possibility of trying to patch in something like this? https://www.ebay.com/itm/2pc-1-Lamp-Bac ... SwstxVB6Y4

They are dirt cheap and seems like it ought to work. Essentially replace the whole inverter rather than just the transformer if you can find room to stuff it in there (intended for laptops).

Curtis Eickerman

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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Thu 08, 2018 9:28 pm 
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Location: Cody,Wyoming,USA
Curtis I am thinking about trying to patch one in as I have the transformer out. I have been searching for about 6 months but found out by heating the unit I can get the brightness back. That has me buffaloed as it measures completely open out of the circuit and I have not been able to measure any secondary heating it uninstalled off the board. I am certain the display is still good and being as careful as I can as it is no longer available and was very evpensive.
Tnx
Joe


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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Thu 08, 2018 9:30 pm 
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Have you been in touch with Icom?

Steve G1XRJ replaced his just over a year ago in December 2016
Watch: https://www.youtube.com/watch?v=2GmPvjG-E8Q
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Greg.


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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Thu 08, 2018 9:45 pm 
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Location: Cody,Wyoming,USA
Thanks Greg a fellow tech in the next town has been helping me with the soldering as with tremors I can't solder is a ICOM dealer and has spoken direct with them using his special account to their service and parts dept. and they are saying it is no longer available any place in their system.
Tnx
Joe


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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Thu 08, 2018 10:06 pm 
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I'll speak to a few fellows tomorrow Joe and report back. it's 21:00 Zulu here. Lol
Bummer about the tremors.

Greg.


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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Thu 08, 2018 10:58 pm 
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If you decide to try to patch in a universal backlight inverter, it might work in the way shown below. Unfortunately the lack of documentation on those inverters makes this a little bit of guesswork. So some experimentation is probably in order before subjecting the 756 to the results. That lack of documentation is why I added the statement about the brightness possibly working in reverse.
Attachment:
ic756backlight[1].jpg
ic756backlight[1].jpg [ 122.25 KiB | Viewed 598 times ]
Curtis Eickerman

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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Thu 08, 2018 11:40 pm 
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Well, simple enough. Let me try and un-abstract this circuit.

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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Fri 09, 2018 1:03 am 
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Location: Wyoming.
Well, here it is.
Image

So, simply put, this thing is driven off of the 14v rail. Q801 and Q802 are set up in a Sziklai (Pseudo-Darlington) pair and is responsible for dimming. The 5v pull up provides the 5v to drive the transistors, and is modulated by the CPU via the DIM pin. The 5v itself is most likely generated by the CPUs own supply. These transistors have a very fast switching time, so im still not sure if its pulse driven or analague voltage driven. The BL enable pin is used to disable the display backlight by pulling the 4.8v drive signal to ground. It is a self biasing transistor, hence why it has no support components.

To wire in, say a MoniServ MS179DI
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You would connect B+ to pin 1&2
You would take 5v+ and tie it and DIM through a 33k resistor each, to pin4

The enable you need to invert the signal. With a normal backlight, 5v is on. With this one, 5v is off.
So, you need to build this.
Image

This inverts the signal so it works.

Finaly, pin 3 and 5 are ground.

Retrofit will look something like this:
Image

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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Fri 09, 2018 2:03 am 
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Location: Cody,Wyoming,USA
Thanks Skylar let me mull this around a little and then I am sure I will have questions on how it ties in and works. Being I am going on 83 years old my mind is pretty slow these days as I lived through tubes and descreet (sic) components way before micro Ps.
Joe


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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Fri 09, 2018 6:00 am 
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Joined: Feb Thu 04, 2016 2:41 am
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Location: Wyoming.
One application note to make, you may need to add a 150k ohm resistor from the base of the npn to ground if it doesn't switch states fully.

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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Fri 09, 2018 12:41 pm 
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Why not try to pulse a high voltage through the secondary and see if that will fix the open?


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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Fri 09, 2018 9:14 pm 
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Joe, I've made a few enquiries.
Will have answers Monday.

Greg.


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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Fri 09, 2018 9:30 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1311
Location: Cody,Wyoming,USA
Thanks Greg I will be waiting. I have papers and circuits all over my desk. I went through this about 6 months ago and struck out.
Joe


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 Post subject: Re: Hurting for help and advice
PostPosted: Feb Mon 12, 2018 6:58 pm 
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Location: Mountains of Mourne. Ireland.
Joe,

good news... ICOM UK have two in stock (reserved in my name).
How many would you like, they are $13.00-US each.
Image
The six dollar standard shipping is 5 to 7 (business) days.
Economy at a fiver is sea-mail, and could take up to 6 weeks!

I am more than happy to pay ICOM for it/them and ship to you.
Greg.

oh... send me your email address via PM (private message).


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