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Author Topic: Project 775  (Read 10348 times)

Offline Josh

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Project 775
« on: March 21, 2019, 2115 UTC »
We should share our HAM projects to encourage (or enrage) one another! Mr Smolinksi, plz consider making a sub forum in HAM radio for that!

Tother day I saw an advert for a likely rig at The Ham Station, called upon said proprietor, and with a deal being struck, I ventured homeward with a Icom IC-775DSP for a pittance.

The upside is the pittance, the downside is the rig needs a lot of repair and an entire makeover, this thing looks like it was dragged behind Brunson's (AE4N SK) golf cart at a hamfest.

A bit about the 775;
The 775 were the flagship of the Icom HF line back in the day, just after the glorious 781, but before the 756 original flavour.
The 775 brought DSP to the line and oddly enough it was an option, an option unlike the typical add in DSP cards as it was more or less IF DSP rather than AF DSP. What this means is there are two distinct modulation and demodulation paths for the 775 - one provided by the add in DSP card, the other by the onboard analog hardware. My guess is it was one of Icom's most costly rigs ever, as far as parts and design. It will produce some 200w of output power with a 28v pa featuring transistors that are rated at 150w each so I might be tempted to run it at 300w if the waveform's clean.
The 775 also has option slots for multiple xtal filters in the 9 and 455 IF lines, some of wich are already populated by high quality filters.
It's also a huge radio, behold;
https://www.youtube.com/watch?v=TiZxQCv4m04
Look at those buttons and knobs!
Come in Tokyo!
HAM nerdvana!

Now about that downside;
The 775 has a known issue with the display backlight cfl circuit where the solder cracks and arcing occurs on the hv secondary xformer, another is it was dropped in transit to a repair shop for the display issue, said repair shop refusing to touch it. It seems most delivery services have instilled a "drop it or you're fired" mentality at their hubs.

Anyway, I'm confident I can overcome the xverter cable connector issues (damaged in shipping) and can have the top and bottom covers bead blasted and powder coated locally, and live with the face if I can't source another, the face is kinda beat up but it's all there. It kinda looks like the HAM only operated the rig when he ate fried chicken, thank god he didn't smoke too.


Project 775

A few years ago I was into the R71 in a big way, with mods and historical notes and everything as it was used by many US gov agencies as well as sigint outfits around the world for many uses, from sigint missions to training. It was often paired with the glorious R7000 to add V/UHF coverage. Even today they're a worthy hf rig.

As I was all about the R71, I came up with some mods and replacements of my own and have parts left over that are perfectly suited for the 775.

One of the mods was to employ the MI204 PIN diode for all input bandpass switching in the front end up to 11MHz, that diode being the one chosen by Icom for use in several hf receiver front ends for VLF to MW. The reason this diode is choice is due the carrier lifetime of said diode, they're simply a much better performer down on the low bands than the typical front end diodes, however they're much more expensive and very hard to find, got mine from Icom years ago. Below about 8MHz these diodes are the cat's ululation, above 8MHz the standard Icom 1SS53 is an outstanding performer even though it's not a PIN diode. The following url has images showing how poorly chosen front end diodes contribute to IMD;
http://jking.000webhostapp.com/TS-940/TS-940_02.htm

What this should lead you to suspect is I have a lot of crap left over from my R71 rage days.

So I'm contemplating replacing the standard front end diodes with the MI204s I have on hand, and perhaps in the 455 IF switching lines too but those lines see only controlled and tightly bandwidth limited rf.

Another mod is replacing the FL80 2.4KHz ssb filter with a FL70 2.8KHz filter, a direct pin for pin swap. The FL80 is choice when you run the FL44A 455KHz ssb filter as their bandwidth matches, however the 455KHz ssb filter in the 775 is the FL96, a 2.8KHz wide filter. Not only will I enjoy much better audio from the 2.8KHz pair, I can sell the FL80 as it's a sought after premium part and as the 775 was one of the last to use the FL80, the one in the rig is fresher than many of the others found on epay.
Also have a 6KHz wide AM filter that can be spliced into the IF strip for better selectivity on SWBC AM and ECSSB.

There's a lot of possibilities to the rig as it stands, if I can get the core sections up and running. If I can't, there's more than enough filters and the DSP module that will make me a profit over the current outlay if placed on qth or epay. That being said, I'd really like to get it going and modded to my likes, a super R71 of my dreams that can transmit.


nerdstuff;
https://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/radcom/1995/12/page72/
https://en.wikipedia.org/wiki/Carrier_lifetime
https://www.alldatasheet.com/view.jsp?Searchword=1SS53
http://www.arrl.org/files/file/History/History%20of%20QST%20Volume%201%20-%20Technology/QX01-03-Rohde.pdf
http://www.ab4oj.com/icom/filters/list.html
https://www.hamstation.com/









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Offline MDK2

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Re: Project 775
« Reply #1 on: March 21, 2019, 2241 UTC »
Isn't the "black arts" board about projects, ham or otherwise?

EDIT, looks like that board was renamed "The RF Workbench" at some point.
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Matt285

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Re: Project 775
« Reply #2 on: March 21, 2019, 2336 UTC »
I googled the rig. It's a great looking radio. I can see how it was the Icom flagship at that time. Wish it had a FL-25 500hz filter in it? I need one.

Offline Josh

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Re: Project 775
« Reply #3 on: March 22, 2019, 0622 UTC »
I googled the rig. It's a great looking radio. I can see how it was the Icom flagship at that time. Wish it had a FL-25 500hz filter in it? I need one.

Did you mean FL52A? The 775 has one, and a matching 9MHz IF 500Hz filter too for utter dual IF filtration goodness where the adjacent stopband attenuation is down around the 80 to 90 dB mark. Had FL52A in the IC703 qrp rig, lovely filter for anything that fit in that passband, mebbe HAM Station has one, can't remember but he had a pile of Icom filters last time I was there. Think I have a FL32A 9MHz IF xtal filter around here somewhere, but that's a filter with the older style of pinout used by the 751 and earlier rigs, can be soldered in or drop in. The newer style filters are close in size but the in/outs are spaced differently... thanks Icom! Sadly, I cannot use the illustrious MI204 diodes in the input bandpass filtering, they're all smt devices and the MI204 is leaded! Now to look for some likely PIN diodes of the smd variety.


Inoue-san interview;
https://www.icom.co.jp/world/news/004/



« Last Edit: March 22, 2019, 0627 UTC by Josh »
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Matt285

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Re: Project 775
« Reply #4 on: March 22, 2019, 1039 UTC »
Yes you are correct. Must have had numerical dyslexia a the time

Offline Josh

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Re: Project 775
« Reply #5 on: March 23, 2019, 1744 UTC »
I see you've a 718, nice rig, kinda a grandchild of the 775. I was going to offer a cw filter but the 718 doesn't have a 9Mhz IF strip, just 455Khz and all I have to spare is the 9MHz filter, if I come across one for 455 I'll let you know.

So far in Project 775, Icom parts has the relays I need to replace those popped off in shipping, but the display tube's no longer available, neither is a face plate. The external cable with the broken connectors isn't a xverter jack, it's for an external receiver and I never use those, so as the solder points on the pc boards are broken I'll just link the two points internally with coax.

Some HAMs have used leds to replace the problematic display tube;
https://www.youtube.com/watch?v=jp5qyuBeIdA

What the original looks like;
https://www.youtube.com/watch?v=0z4hd0LSFho
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Matt285

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Re: Project 775
« Reply #6 on: March 23, 2019, 2225 UTC »
Oh well, I'll come across one somewhere. Yes I really like the 718. Its a simple rig with a nice screen and easy layout.

Offline Josh

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Re: Project 775
« Reply #7 on: March 24, 2019, 1831 UTC »
Starting the cleanup and disassembly as well as perusal of service manual. One nice feature noted in said manual is the IF strip is an honest 15Kc wide in wide filter am mode, freaking ossum for ambc audio quality. In ssb you can go 3.3, 6Kc total but it's dsb, not ssb then. The medium filter setting nets you 6Kc width in both 9MHz and 455Kc IF strips, the 9MHz IF filter being optional, and I have one on hand, perfect for swling.

(These wider bandwidths are why I miss my TS870, the 870 ambc audio sounded like you were in the studio, the downside to the 870 is the filtering isn't very sharp.)

Then the 775 detracts from that potentially ossum audio quality by not employing dsp to demodulate that am signal, it uses a diode, and diodes are noisy. Dsp can produce mathematically perfect modulation and demodulation sans distortion = why you want dsp for this. The 775 dsp only modulates and demodulates bfo modes; ssb, cw, and rtty, not am or fm. Oh well, diode rectification can sound good, just replace the diode with a schottky/hot carrier type, bias it a bit perhaps, adjust the output capacitances to recover lows and there you are with studio quality audio out.
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Offline Josh

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Re: Project 775
« Reply #8 on: March 25, 2019, 1744 UTC »
Recalled that some Italian HAMs took their 775s to nerdvana with some serious mods;
http://www.pensioneitaliacapri.com/ham/IC775-Progetto-Modifiche-2009_Finale.pdf
You can translate it online if you wish;
https://www.onlinedoctranslator.com/translationform

Gian and Nick carved up their 775 and replaced or modded quite a lot of the inners of the 775, to include mixers, active vco filtering, roofing filter swaps in various IF strips, etc, read the pdf if you want to know more.

One of the takeaways I got from the pdf was the 9MHz IF roofing filter I'd not noticed. This filter sets the 9MHz IF bandwith to 20KHz right after the mixer, they replaced it via a factory Icom part that was only 6KHz wide. This is great if all you want to pass thru that IF strip is 6KHz wide or less, in itself this should greatly increase tolerance to strong nearby signals while not compromising the desired signals.

Having a filter right behind a mixer is a good idea, because in most mixer cases you send in two frequencies to mix and you get four out (due to images) when you only wanted one freq.
The way to properly terminate a mixer is with a diplexer circuit that terminates the undesired product freqs gracefully. The filter is a brute force means to that end, as well as reducing noise in the IF strip as a typical IF strip can be 10s or hundreds of KHz wide.

The 6KHz wide 9MHz IF filter is too restrictive for someone who wants to have a truly wide bandwidth like 10 or 15KHz, but Icom has other filters of the same case and pinout design and the same center frequency but with different bandwidths. 9M6A1 FL-116 is the 6kHz BW filter - the Icom IC706 employs these for wide am, part number 201 0000 950 if you want one from Icom. The standard IC706MKIIG has a 15KHz filter, this is the one to order from Icom if you want to pass ambc sigs yet still get some tighter filtering over the standard 20KHz wide filter. I'll install a 15KHz filter here, so glorious wide ambc and hfbc sigs can flourish. Flourish I say!
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Offline Josh

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Re: Project 775
« Reply #9 on: March 26, 2019, 1921 UTC »
Preliminary inspection complete.

First off, I'm not set up to work on a rig this massive! Good thing homes have floors.

This thing's missing a lot of case screws, mostly for the faceplate, wich can be an indication people have been rooting around inside and not bothered to replace the screws. Simple enough to remedy and Icom has the screws, I checked. Icom likely still uses many of the same screws in all its rigs.

On the shipping damage front, I was very worried there would be broken boards due the connectors soldered to said boards being pushed in and broken off. Boards are fine, just the leads to the components have sheared off, an easy fix. The external antenna connector jumper apparently hit the floor, broke off two different boards, and in one board pushed two relays far enough that their leads were broken. So far I need 3 relays that Icom says are 11 bucks each, will try to find them cheaper. I suppose I could repair the relays easily enough but the leads are really thin so new is likely best.

On removing the bottom cover, I noted some weird buildup that at first reminded me of mud dauber wasp activity, but tasting it revealed a distinct waxy flavour. Na jk, I touched it and it's wax. So where does wax come from in a 775? As expected, the stalagmites of wax (or are they stalactites?) emanate from the pll and dds area, as provenanced by replacing the cover and seeing how the wax stalagmites and vco/dds openings aligned. This indicates the rig either ran for long periods of time, or the wax wasn't very temp stable. The worst part of this will be everything inside the vco/dds cans might be wax covered due to capillary action, to include the vco tuning caps, then again this wax just might be a beneficial preservative in nature. Have to open them cans and find out.

The reason companies apply literal gobs of wax to vco/pll/dds circuitry is due the nature of solid wax; easily applied in liquid state and then hardens to a stiff support structure. The reason we want to stiffen the vco/pll/dds circuitry is to keep mechanical but not electrical vibration to a minimum. Another issue some waxes and glues present in electronic circuits is that they can become hygroscopic over time, meaning they can absorb humidity from the air and retain it, causing changes in the tuned state of nearby electronics. The Kenwood TS 440 and 940 were/are notorious for this. Removing and replacing this wax is a common procedure in hf rig repair, often hot glue or epoxy is used to replace the wax. I prefer to use something that can be more easily removed than epoxy.

This secret and forbidden love for water that wax seems to have is one of the reasons why one must replace every wax capacitor inside old radios, the wax has had decades of absorbing moisture, and the acids in the paper the cap dielectric's made from have come out and are all combining to transmogrify (lol "transmogrify" is actually in the spell checker!) those caps into a very poor form of resistor.

On the vco/dds front, have to get the rig fired up and warmed up before vco/dds tuning can commence, as well as a complete alignment as a rig this glorious warrants. Every used rig I've ever had needed at least vco/pll.dds alignment, and many could use a full alignment. These full alignments can take hours, but are kinda satisfying to see a rig that before seemed a mite deaf come out with much better than than published sensitivity and selectivity.

Here we should have a talk about manuals since we talked about vco/dds.
To do any real service work on these rigs you need a service manual. simple as that.
I've had about every Icom hf rig, and since getting involved in the madness that is personal computing, have aggregated gigs of user and service manuals on pdf. If you have a rig, its service manual is likely out there on the web for free. If you want a hard copy, it's so easy to take that manual via flash drive to your friendly local printers and have them do one up for you, complete with holes for your three ring binder. Try to splurge and get full color rather than black and white as some schematic overlays use two or more colors to show underside traces and so on.

This faceplate really needs replaced, it's scarred and scratched and looks like someone spilled milk on it. I suppose a trip to the bathtub with hot soap and water will make it look as best it can, considering. I don't trust chemical cleaners such as the spray on types people use to clean electronic devices other than say bar soap. hot water, and a dish rag anymore for cleaning items like radio faceplates due the chance the chems might wipe away printing, or eat plastics.

On checking the various board screws for tightness, almost all of them so far have proven to be about finger tight or loose. The inside is very clean overall other than the wax issue wich is contained to the bottom cover and the insides of the vco/dds cans, so I wasn't expecting every fing board to be loose but that's trivial to deal with. Every rig I get, new or used, has all the screws loosened and tightened or at least checked for tightness. I guess after traveling across the ocean from Japan in some huge creaking container ship and decades of use have temperature cycled the rig, causing the screws to be loose, at least that's my fantasy.

On the top and bottom covers, no spraycan from walmart will be restoring the deep gouges and rusted spots, these things will have to be bead blasted and powder coated or spray painted.





This has been cathartic and fun so far, that's it for now!


« Last Edit: March 26, 2019, 1925 UTC by Josh »
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Offline Josh

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Re: Project 775
« Reply #10 on: March 28, 2019, 0354 UTC »
Why alignments are wonderful things;
https://www.youtube.com/watch?v=3MpP1K2pbSA
This vid's from the TRX Bench, a great channel for those interested in HAM radio repair.
Most sdr rigs will never need aligned, they align themselves every time you fire up the app. With analog rigs, the older the rig, the more likely it could use an alignment.

Most rigs made by Icom have a Japanese version not sold outside the home islands. In some of the youtube vids for the IC775 you will see rigs with a black display border and illuminated nomenclature, this is likely the home islands version known as the ICOM 775DX2, same as the euro or American version but with the display oppositely polarised and in some cases 100w out rather than 200w. There is or was a Japanese regulation where all HAMs were allowed on hf with 10w or perhaps more regardless of license class, they considered the low power a limitation on what damage new HAMs could do to the hf bands. When the IC751A ruled the land, Japan had a 10w qrp version for their lowest license class, everyone else got 100w versions. Most lcd displays can be changed from illuminated nomenclature and dark background to the reverse, you'd need to peruse the service manual for said display to see how.

Now back to the home islands Icom naming convention, most Icom rigs sold in the US and the eu are also sold in Japan, just with different names. For example, the IC746 Pro known around the world is the IC-7400 in Japan.
« Last Edit: March 28, 2019, 2110 UTC by Josh »
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Offline Josh

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Re: Project 775
« Reply #11 on: April 08, 2019, 1837 UTC »
Relays and case screws ordered and on the way, so stoked!
The kind lady at Icom Parts who took my order discussed the glorious 775 at length with me, and made mention of ebay perhaps being a source for parts Icom no longer had on hand. Must admit hadn't considered ebay as a parts source and checked them out.



Suddenly there's several 775 parts/modules on the screen! You need a pll board? Got one working pull for $100. Need at tuner unit? Got one too. The further I looked into what the seller had on hand raised my hopes greatly. Here was a top cover in very good condition for only $30 ($34 shipping), and its mate for another $30. He had several other parts modules for similar HAM rigs that made me wonder if he buys HAM rigs then vivisects them to sell off the harvest, not sure how to feel about that practice but if it gets me a new faceplate I am all for it I guess. I followed his list to the end and no joy, no face plate for me! Where did it go to? He had to have it if he has the rest of the rig.

The covers can be bead blasted and either powder coated or spray canned into niceness, not gonna shell out 30 a piece and another 34 shipped when rustoleum can do wonders for pennies.
« Last Edit: April 09, 2019, 1754 UTC by Josh »
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Offline Josh

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Re: Project 775
« Reply #12 on: April 19, 2019, 1908 UTC »
Follow along as the surgeon makes the first incision;
http://photos.meekfarm.us/GalleryThumbnails.aspx?gallery=4862380
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Offline Josh

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Re: Project 775
« Reply #13 on: April 30, 2019, 0017 UTC »
Relays and new rca jacks installed, checked settings and powered it up.

https://www.youtube.com/watch?v=0VkrUG3OrPc

Bands checked, power out is good, controls seem responsive, dual watch works, all with a face only a mother could love!

Now on to the self dimming display!
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Offline Josh

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Re: Project 775
« Reply #14 on: May 01, 2019, 1838 UTC »
Self dimming display is no longer an issue, now on to tuner motors that seem to be frozen.



A fix for Icom tuner motors;
https://www.youtube.com/watch?v=UdY6RhNOCWg
« Last Edit: May 02, 2019, 1954 UTC by Josh »
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