I've got two pretty dirty, pretty beat up FT901's. I want a backup for my working 901-DM and I had to decide which of the two I should dive into and bring back to life. The D was the cleaner of the two but close inspection showed some serious black charring on one of the ceramic bandswitch wafers. So I decided to go with the dirty DE. I cleaned out the chassis and the modules as best I could and re-populated it with the best of the modules that I had.

I'm usually pretty nervous anytime I power up a new-to-me rig. Normally I double check the whole power supply area for obvious shorts because I have a real aversion to electrical sparking. It goes back to a skiing trip when I was a kid. Somebody had put their wet skis up against the wall in the room where I was sleeping. In the middle of the night, in this strange bunkroom, the melting snow had run down the wall into the AC outlet and lit up the room with a loud bang. I jumped out of the top bunk and landed on my feet in the pitch black room before I was even awake and aware of what happened. It shook me up pretty good and since then I've always had more than a healthy repect for AC voltage.

But uncharacteristically, I decided to power up the DE without double checking anything. I switched the Power Switch on, the rooms lights dimmed, there was a slight popping sound from the rig, and that warm smell of something heating up. I quickly shut the power off. I felt the power cord and it was warm. Really warm.

The power transformer was shot. I measured a couple of ohms across one of the primary windings and zero across the other. So that's where this story starts. Time to dig the presumed good power transformer out of the D and put it in the DE.

The Good Transformer

No turning back now. The good transformer liberated from the D chassis.

The Bad Transformer

Hard part: Remove the bad transformer from the DE chassis without losing any of the wire tape labels or breaking anything.

The good transformer went back in but no way were we going to power it up again without checking everything. Turns out the Rect B board had all 4 diodes shorted and 3 of the 470k resistors bad. Not only that but I found that the main fuse had been jumpered. Thats why the fuse never blew for the first transformer.

I rebuilt the Rect B board from scratch. The modern filter caps only had a 10mm spacing between the lugs which was too close to fit into the circuit board slots. I had to use the Dremel tool to widen the slots and managed to fit them in. Some of the circuit board foil landings got beat up pretty bad but with judicious soldering I was able to get everything connected.

The Rect B board went back in fairly easily. I had already checked the Rect C and A modules in my working 901 so I knew they were good to go. I tripled checked all my wiring. I triple checked all my solder joints. I quadruple checked for inadvertent broken wires or bent pins from flipping the rig top to bottom so many times.

With all the tubes out I started again with the Power Switch off and brought the Variac up slowly to 110VAC. Zero current draw so no jumpered fuses this time. I switched the Power Swtich on and brought the Variac up again. At 80VAC the meter light and frequency readout came on. At 95 VAC the readout stabilized. I brought it all the way up to 117VAC and here's what I've got. No smoke and lights. Barely audible CW and SSB on 40 meters but the 2 basketcases have been combined into a fixable FT901-DE.

Good Receive RF, Flaky Audio

First things first. Adjusted the 6VDC power supply for +6.01VDC. Then started looking for the weak RF and Audio. Cleaning the antenna relay contacts brought good RF levels to the S-Meter. Meanwhile, the one remaining S-Meter lamp went out but RF levels were good. Next poking around for good audio level coming and going. The problem seems to be centered on the front panel switch bank. Massaging the AGC or wiggling the APF switches brings the audio back. After another cleaning of both switches good audio levels are there most of the time. We'll look into it in detail when we pull the front panel off again to fix the meter lamps.

Decent Transmit

Moving over to transmit I adjusted the bias control for 50mA and hooked up to the dummy load. I'm getting surprisingly decent SSB output on all bands. Usually I just throw any working tubes that I have available at a new rig and just go with it. This time I went through my spares and pulled out the strongest 12BY7 and 6146's that I had. I guess that makes a difference. I'm getting a full 100W output on all bands.

I went to test it on 20 meters. Answering a Russian CQ I pulled the mic handle and nothing happened. I peered around to the side of the rig and saw there was no filament on the driver tube. I massaged the Heater switch and it came back on. Then I watched as it disappeared again. I shut down and pulled out the schematic. The 12.6VAC filament chain from the Power transformer: Power plug, Heater switch, R10... and then I got lost in the maze of the schematic. I knew that the path went through the ACC plug so I wiggled the plug a little in its socket and tried again.

This time the heaters came on. And stayed on. Long enough to work an LZ2 on 40 meters. So a couple of quirks so far but not a bad start to getting this 901 back in shape.

Checking Out All The Modules

With a somewhat functioning 901 it was time to go through all the spare modules I've accumulated from the 2 chassis' and see what's good and what's bad. I've been retired now for almost 3 years, but I spent most of my life as a Broadcast Maintenance bench tech. One thing you always wanted for live televison was spare units hanging around the shop to be ready for emergency use. That idea has been ingrained in my brain so I cherish the idea of having a shelf full of ready to go modules for when one of them goes south in my main 901-DM rig.

It took a few days but I wound up with a pretty good haul of OK modules. Of course the most important ones were the bad ones. The VFO powers up but it takes off on it's own frequency excursions oblivious to your hand twirling the knob. Someone must have sat on the Rectifier C card. The metal mounting bracket sheared off the board on one corner and it's got a neat diagonal crack right across the board. Someone tried to solder across all the broken copper strips so that board is for parts only. The readout obviously has a problem. It's been over 40 years since I last had to remember anything about TTL logic, but that might be a fun project to dive into and see what I can remember. Maybe. Some day.

Front Panel Down

So far the big problems are dead Meter lamps, intermitent audio coming from the front panel switch bank, and mysteriously disappearing filament voltage to the tubes. I pulled the front panel off and started with the Meter lamps

I'm very (maybe too) cautious when it comes to the possibility of inflicting further mechanical damage on boatanchors. I toyed with the idea of leaving the meter lamps alone and just enjoy using a working transceiver without meter lights rather than risk breaking the meter trying to fix it.

But there's that bench tech in me that says, "No. It really is broken. You need to fix it. It was put together by humans. It can be taken apart and put back together by humans". Luckily I have a spare Meter than I can experiment on. The plastic facecover came off easily with some gentle prodding from my trusty Red Xcelite. Both grain of wheat lamps measured open. I ordered some new ones and we'll have to wait until they show up next week to continue on here.

12V Lamp - 8V Circuit

Well...the replacement 12V lamps work. But they're certainly not as bright as the original 8V grain-of-wheats.

I suppose if I had the 2 rigs setup side by side it would bug me no end to always be looking at the different meters. I thought about bypassing R10 the dropping resistor and taking the 12V direct from the power transformer. But that would mean sticking the soldering iron down inside a narrow space to get at the Heater switch lug. And I'm done messing around with the front panel down. I can feel I'm on the verge of breaking something the more I poke around on the insides.

While waiting for the new lamps to show up I tried to get the switch assembly out to get a good look at the APF switch to see what was up with the disappearing audio. I could only get the assembly out so far without pulling and pushing against things that didn't want to move. A sure sign to me to just stop pushing, button everything back up and hope that you still have a functioning transceiver when you power it up again.

Which I'm doing, but now I notice some resistance on the left hand side when I try and put the Front Panel back on. I had to angle the panel back on with the Switch assembly and Meter mounting screws all loose to make it fit. And I still had to put some pressure on it to get the 3 left hand Front Panel screws to line up with the chassis holes.

So no more tinkering. Maybe I'll order up some proper lamps and install them in the other meter. But now the knobs are going back on and I'll make sure I've still got a functioning 901-DE.

No Damage Done - A Working Rig

With the Front Panel back on and all knobs in place it looks like I've got a working rig. At least on 40 meters, with a contact all the way down to West Virginia. Re-jiggering the Switch assembly actually made the switches move easier, so maybe that was the original problem. Audio levels have been constant and stable. The tube filaments have continued to glow constantly so no answers yet to that glitch. And I'm in the market for a missing AM Filter. I'll keep the covers off a little longer and play with it from the bench until I see if I can find one.