[ICOM] New Owner IC-781

[Traian Belinas]

Dear Heinz,

First of all, you don't have to remove the aluminum alloy front panel
and/or front panel knobs for to dismantle the CRT module.
After removing the transceiver top and bottom covers, you can gain
access to the CRT module assembly and remove it only after rotating
downside the entire front panel assembly (untighten the lower two front
panel assy small fixing screws and completely remove the two other upper
ones - don't confuse them with the big ones which are fixing the
alluminum alloy front panel only); then you may to slightly rotate the
entire front pannel assy downward and may get out the entire CRT module
from the radio (after removing its top cover and then the mounting
screws at the bottom cover and its wire harness, of course).
But don't remove the CRT module at all (yet)...
When opening the CRT module top cover, take care about the AT preset PCB
from the top of the CRT case, to not make shorts to GND when working on
the CRT module and power on.
The CRT module have some adjustments inside, on its PCB.

First, there is a row of 7 adjustments (small pots), near the CRT's PCB
right edge (as looking from top, from the front of the radio).
Two of them are BRIGHT and SUB BRI respectively.
As you know, these two are adjusting the CRT brightness.

BUT, and more important, there is another small pot djustment, it is
located on the same CRT module PCB, just near the fuse.
This one is adjusting the amplitude of the CRT  video signal, i.e. the
CRT Contrast.
>From my experience, for both the R9000 and IC781, I had to increase the
contrast adjustment for having a good image.
It has a better effect for old CRT than the brightness increase and I
think you should try this first, before any other intervention.

Also near the same area, there is a bigger potentiometer (horisontal
shaft).
This one adjust the CRT focus.
If the image is not crisp, you may adjust it;
But if you can see (separate) the individual scaning lines when looking
very close to the CRT center image and if  the image is not very
foggy/unfocused at the corners, then you may leave it as it is, as
adjusting it while the module is still inside the radio is some
difficult (there is a hole dedicated for this, but it is located at the
CRT module back panel, so imposible to adjust by there while the module
is still inside the radio).
If you will replace the CRT, then you may  have to readjust all of these
pots, of course.

When adjusting the brightess, do not exagerate.
Don't adjust it so high as the background (normally black) to became
very bright/amber because using it this way for a long time will shorten
the CRT life by loss of the cathode emission and tend to faster
apearance of the burns on the screen.
If adjusting the internal contrast and brightness don't give results,
then the CRT may be bad/used (because of long use).
If for to obtain a decent brightness and contrast you have to turn up
very much these adjustments (near to max) and the focus is bad and
impossible to improve, then may also have to replace the CRT.
Of course, for both of the radios I had (IC781 and R9000), the CRTs had
burns, they are normal for these such old devices, unless they have very
low hours on it and were used at low bright/contrast adjustments.
The burns have not to worry you much if they are not very bad and if the
image is ok,  you may not need for replacing the CRT unless you want a
very bright and high contrast image. The R9000 is still ok at the new
owner (sold two years ago) and have good picture even if had burns.

The 125$ price is not low for a such spare CRT, but not high for the
ICOM users which need them indeed.
At this price may buy an entire 17" CRT computer monitor...
What is interresting, I saw at Friedrichshafen hamfest in 2002 some
brand new 5" color TFT/LCD modules (B/W ones exist also) which accept
CVBS input signal, so they shall work (at least were compatible
regarding the input signal) for the IC781/R9000.
Don't know about the mechanical issues (if it will fit or not and how to
fix it inside, the same about the power requirement and connectors) but
they were not expensive then for what they were doing  (about 200 Eu at
that time, and for sure they are cheaper these days). Were sold by
someone which had to do with the video surveillance systems.

Other info, from previous experience.
The 781's switching power supply PCB may get burned and damaged because
of overheat.
You may check for this.
Mine was also affected.
I have replaced all the critical parts (filtering capacitors, voltage
adjustment pot, some resistors) with very good quality ones.
I have used 105C electrolytic capacitors from very trusty sources; the
ones for the +15V and +30V line were replaced with some larger size
ones.
The voltage adjustment tiny pot was affected by heat and I have replaced
it with a high quality sealed multiturn one (adapted a very good quality
military use russian one, with sealed metallic body). This because if it
affected, it may cause overvoltage at the output.
I understand that failure caused by PS overheat is a common problem for
the IC781 and the R9000, because of much heat and poor cooling of the
PS.
Indeed, the IC781 blower should cool the PS also, as an air circulating
window exist between the blower exhaust and PS compartment, but that air
have no way to travel over the PS board, as the PS compartment is
closed/sealed, the theoretical  incoming airflow from the blower can't
go out, the PS back cover having no holes for the air to get out. It is
like trying to cool a power tube while closing the tube's chimney air
exhaust! The PS compartment is just presurised but not cooled and the
PCB is like being located inside a hot oven...
The Sherwood modified PS back cover and fan will avoid the PS
overheating.
If you intend to keep this transceiver for a long time, then the cooling
kit from Sherwood is strongly recommended.
It will make a huge difference for the PS heat.
I have used an 3" external fan fixed on the R9000 back panel, and even
if the back panel holes were tiny, the heat was much reduced.
I will send you some pictures off list.

Hope this to be of help, and I would like to hear about yours and others
experiences regarding the IC781.

73,
All the Best,
Greetings from Bucharest,
Traian, YO9FZS




[ICOM] New Owner IC-781
hbreuer at debitel.net hbreuer at debitel.net
Thu May 12 06:00:29 EDT 2005

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Hello,

I am a new owner of an Icom IC-781. I had it on my wishlist for about 15

years and finally found one at a price I was willing to pay.
It seems to be ok and looks very good but the display is rather dim. I
set
the internal brightness control to maximum but it is still difficult to
read at daylight.
I guess the CRT is in its final days. I already ordered one from the
evil
bay. I downloaded the service manual but could not find any info on the
CRT
unit. The CRT unit seems to be a standard OEM device and was not made by

ICOM.

Before I start to dismantle the 781 in order to replace the CRT I would
appreciate any input from the group. It seems that I have to remove all
knobs to be able to pull the front panel which should give me access to
the
CRT. Anything else I should know?

Thanks for your input and best 73
Heinz DH2FA, KM5VT