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Author Topic: ICOM IC-251a DC to DC Converter fried  (Read 1527 times)
WA7KGX
Member

Posts: 104




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« on: February 18, 2013, 07:38:35 PM »

The DC to DC converter  identified as IC 18 DP-4 has been fried.
The display is dead and the PLL is off frequency.

According to the schematic, it takes in 13.8 volta and produces -10 volts for the PLL
and -18 for the display. 

It also has two lines each labelled H going to the display.
Heater(s)?     What voltage Huh

Any help would be appreciated as the radio works otherwise and has plenty of room
for mods.
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W9GB
Member

Posts: 2626




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« Reply #1 on: February 19, 2013, 06:44:41 AM »

As I remember, the IC-251a used a VFD for main display.

Contact Scott at MTS.
http://www.angelfire.com/biz2/mts/

He worked in Icom Service when these were new and under warranty.
He also has some "parts radios" and hard to find components.
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AD4U
Member

Posts: 2173




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« Reply #2 on: February 19, 2013, 10:49:48 AM »

Ditto on Scott.  I sent him two ICOM radios in the past year.  One was an R71A HF receiver which is 20? years old.  The other one was an R7000 DC-Daylight receiver which is around 30 years old.  Both were repaired and updated and perform as new (or better).

Dick  AD4U
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K4JJL
Member

Posts: 498




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« Reply #3 on: February 19, 2013, 01:59:00 PM »

You can see the if the heaters work in a VFD by looking at the wires running horizontal across the screen.  Watch the tension springs at the ends when you power it up.  The heaters actually grow slightly and the wires will glow a dull red ever so slightly when heated up.  I think they have around 3-5V AC on them (which is why most VFDs have a small transformer on them).
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