Yaesu FT-902DM restoration

[N8YX]

Why I'm doing this, I have no idea. Maybe because I've had no takers on the sale of the rig plus a box full of parts, and the thing has been sitting in my dining room/project pile for far too long. Maybe it's because the first generation FT-901 is one of several pieces of equipment which lured me into ham radio - though I've bought, fixed and sold a few of that line over the years.

Maybe it's because - after all these years - the rig is still very high in the Sherwood Labs test rankings. And it's a worthwhile successor to the '901 series, having addressed most of that set's ills.

I bought this particular rig from FleaBay a while back, intending to use it as a donor radio for some projects. Two of which were WARC conversions of FT-901DMs I formerly owned then sold. (That's where the missing crystals went...!)

A couple of things about the 902 I dont care for as compared to the 901: First, the frequency readout and dial scale are yellow, as opposed to red and blue (respectively). Second, the VFO itself tunes in the opposite direction as its predecessor, making operation with the accessory FV-901DM a bit tiresome. The VFO units can easily be swapped between models, and I found a '901 unit online...which is what kickstarted this project. Similarly, the display LEDs can be swapped for a color of the user's choice - if one does enough parts sleuthing.

So now I have a partially disassembled '902 on my workbench. First order of business was to replace the cracked nylon gear which sits on the PA Loading variable capacitor shaft, transmitting motion from its control shaft. (Remember that stash of parts I mentioned? A spare was found therein.)

Much more to come as I work through this set and identify any problems (real or potential) then address them. Pictures too.

[WØTKX]

I still have mine, just sitting there.
Remember? No transmit.

Have
No
Time
To
Fix
It

:(

[N8YX]

I still have mine, just sitting there.
Remember? No transmit.

Have
No
Time
To
Fix
It

:(
Got heaters?

HV on the tube plates? Screen voltage?

If you hook a scope to the RF Out (transverter) jack, do you see ~100mV RF when the Preselector is peaked and the Carrier control is advanced while the Mode switch is in CW and the Tune button is depressed?

[N8YX]

Back into the rig after the holidays. Most of the Christmas/New Year's break was spent researching spare parts, mods, finding needed supplies and tending to mechanical glitches.

First things first - a bout with the air compressor on my back porch to blow out the accumulated grunge. All of the plug-in boards and the tubes have been removed and stored a while ago - remember I was originally going to sell this project as a parts radio?

When I received the rig several years back it powered up correctly. So...looks like the transformer is in good shape. All the rest can be fixed. On to the mechanicals. I checked the various controls for proper operation and found that the PA Loading control wouldn't turn its associated capacitor. Close examination of the drive train revealed a cracked nylon gear on the loading capacitor shaft. (FWIW, many hybrids of the area used these; they're coupled to their tuning shafts by chains. Many of the all-nylon variety end up cracking due to age and stress.)

I knew of Greg, NR6C through the Tempo 2020 Group:

http://nr6c.com/TEMPO%20SPROCKETS.htm

He reproduces a set of gears for that rig and also offers them for Kenwood's hybrids. I contacted him, described the problem and offered to send the cracked gear as a model. (Luckily, I'd found a spare brass gear from a defunct '901 and had the '902 working again - but it's nice to have options...and to help other hams whose rigs have cracked parts.)

Greg made a set of these (old gear shown for comparison purposes) and they're inbound. Coincidentally, the FT-101Z series rigs use the same 15-tooth gear.

15126

They're 3D-printed onto a brass hub and are a stronger part than stock. I'll be writing up the installation instructions for him when they arrive, using my rig as a model.

I also needed a top cover. An ad on one of the classified sites brought a response. Though a number of factors conspired to delay its arrival, the cover finally arrived today. (Special thanks to Greg, KG6YV for answering the ad and providing the part.)

The only remaining cosmetic item is a front panel. The one on the rig is a bit rough but usable, and I'll continue to scour the 'Net for one while I rebuild the rig's electronics. If push comes to shove I can always try my hand at a little touch-up bodywork.

[K7SGJ]

He does nice work. My son makes all kinds of stuff with his 3D printer and sells a lot of it. When I see some of the prosthetics that can be made with a 3D printer, especially for children, I am just amazed; and seeing these gears, I guess it shows that what can be done with these machines is only limited by the imagination.

[N8YX]

The FT-901D and FT-902D series rigs - along with the FT-980 - had a Curtis 804x based keyer assembly as an option. Early version used an 8043; the later one employed an 8044. Both are interchangeable. Both chips have been discontinued. And I have a dead board on my workbench. So...what to do?

DL4YHF to the rescue. Found out about this solution through the FT-901/902 Group: http://www.qsl.net/dl4yhf/key_circ.html

Pic of OEM ($60+ NOS) board:

15128

New PIC-based keyer built onto a protoboard and installed in a radio:

15129

I need a few of these keyers for various Yaesu projects around the shack. Time to set up a production line some weekend and build some.

[N8YX]

Another neat but often overlooked feature found on this series of radio is one which belies its contesting heritage. See the DIN connector immediately above the fan power connector?

15132

It outputs band-data information (+12V upon selection) and follows the band switch position. 160-80-40-(30)20-(17)15-(12)10, for the FT-901 and 902, respectively.

Now...what can I do with the feature?

Simple - interface the rig to this: http://www.dunestar.com/store/Multi-Band-Remote-Switched-Bandpass-Filters-pid-3.html

15133

Or to this: https://www.arraysolutions.com/filters/filtermax-4

15134

And automatically switch the BPF via the radio, thus allowing close-proximity (read: city lot) multi-band operation without fear of damaging the radio's front end. Each filter requires +12V to a control pin to activate a given "bank". Not quite a mod or repair, but a nice addition to the shack - one that will make operating more enjoyable to boot.

Yaesu's engineers really were thinking ahead when they designed this set.

More to come...

[w2amr]

Back into the rig after the holidays. Most of the Christmas/New Year's break was spent researching spare parts, mods, finding needed supplies and tending to mechanical glitches.

First things first - a bout with the air compressor on my back porch to blow out the accumulated grunge. All of the plug-in boards and the tubes have been removed and stored a while ago - remember I was originally going to sell this project as a parts radio?

When I received the rig several years back it powered up correctly. So...looks like the transformer is in good shape. All the rest can be fixed. On to the mechanicals. I checked the various controls for proper operation and found that the PA Loading control wouldn't turn its associated capacitor. Close examination of the drive train revealed a cracked nylon gear on the loading capacitor shaft. (FWIW, many hybrids of the area used these; they're coupled to their tuning shafts by chains. Many of the all-nylon variety end up cracking due to age and stress.)

I knew of Greg, NR6C through the Tempo 2020 Group:

http://nr6c.com/TEMPO%20SPROCKETS.htm

He reproduces a set of gears for that rig and also offers them for Kenwood's hybrids. I contacted him, described the problem and offered to send the cracked gear as a model. (Luckily, I'd found a spare brass gear from a defunct '901 and had the '902 working again - but it's nice to have options...and to help other hams whose rigs have cracked parts.)

Greg made a set of these (old gear shown for comparison purposes) and they're inbound. Coincidentally, the FT-101Z series rigs use the same 15-tooth gear.

15126

They're 3D-printed onto a brass hub and are a stronger part than stock. I'll be writing up the installation instructions for him when they arrive, using my rig as a model.

I also needed a top cover. An ad on one of the classified sites brought a response. Though a number of factors conspired to delay its arrival, the cover finally arrived today. (Special thanks to Greg, KG6YV for answering the ad and providing the part.)

The only remaining cosmetic item is a front panel. The one on the rig is a bit rough but usable, and I'll continue to scour the 'Net for one while I rebuild the rig's electronics. If push comes to shove I can always try my hand at a little touch-up bodywork.The replacement gears are really cool. Don't worry about the front panel, gives it a bit of character. HI

[N8YX]

The replacement gears are really cool. Don't worry about the front panel, gives it a bit of character. HI

I thought about that, George...and it's a character, all right! ;)

If I can't cleanly touch up the edges with Humbrol 77 (as a restorer has done and documented) I'll leave the area around the heater switch alone and keep scouring the 'Net for a front panel or for a junker radio from which to steal a few parts. Problem is that no one wants to part with a '902.

[N8YX]

Bumping the thread a bit.

Finalized the gear design with NR6C and got a prototype set installed in the '902 project. This photo is representative but very close to the finished product:

15281

Also managed to snag an OEM power connector (for an AC cord) and another FT-901DM in great shape. It came with a lot of spare assemblies and parts, a couple spare IF filters. While I'm documenting the gear installation process, I can actually use the new arrival on the air. So...naturally...I tore into the thing and am in the process of adding the XTAL/VCO Board components required to enable the (hidden) Aux Band spot.

There are two versions of the FM Board used with this radio; one with a large, optional solder-in 8-pole crystal filter (XF-8.9GF) and another which uses cascaded Murata 4-pole filters. The former is desirable if using the rig on 10M FM as the channel spacing is tighter than on VHF. I had one with a filter installed, another without...and as luck would have it, scored a NOS OEM filter from R&L for the princely sum of $20. That board is now in the '901, where it works great. The second of these goes in the '902 upon restoration.

More to come.

[K0RGR]

I had a 902DM that was a pretty decent radio, but it developed some issues over time. The biggest annoyance was a need to occasionally reseat all of the circuit boards after a thorough cleaning of the contacts. Then, after a realignement, it would be back up to snuff.

Something happened to the VFO on mine. The knob seemed to be eccentric, and over time, it became more so, making it difficult to operate. I ended up using the external VFO most of the time. It was like it had been hit very hard with something, bending the shaft, but to my knowledge, it never was.

[N8YX]

I had a 902DM that was a pretty decent radio, but it developed some issues over time. The biggest annoyance was a need to occasionally reseat all of the circuit boards after a thorough cleaning of the contacts. Then, after a realignement, it would be back up to snuff.
That's one which I've never experienced. High humidity in the shack? Other environmental factors? I've heard of people putting Vaseline or dielectric grease on the edge connectors to keep oxidation to a minimum. DeOxIt might be another option.


Something happened to the VFO on mine. The knob seemed to be eccentric, and over time, it became more so, making it difficult to operate. I ended up using the external VFO most of the time. It was like it had been hit very hard with something, bending the shaft, but to my knowledge, it never was.
The weak spot in any Yaesu rig of the period appears to be the tuning mechanism. Fortunately, I have a complete spare VFO from a '901DM plus another of those in parts - and the '902's setup will be swapped for the one which tunes "backwards". All of the 90x VFOs here at present operate smoothly.

My FR-101's VFO, on the other hand ... :angry: