Yaesu FT-902DM "Restoration" Part Three

Hi,

So onto the second one the PB-1708A Rectifier A board.

Here it is ;

As you can see if you look carefully - overall not in bad condition but the two capacitor on the right look a slightly different colour and so that might indicate that they have a problem.

Either way they will get replaced with new quality 105deg electrolytics.

On the underside of the board (right) you will see the

 usual Yaesu soldering but look more closely. I've circled in red a 'blobby' or poor solder joint. Being entirely fair about it - it might have been due to heat but I think its been like this from the start 

So work starts - removed the four vertical electrolytics - again be careful they have the yaseu 'glue' to hold them still when the unit was subject to vibration when it was used mobile (!!!).

Here are the capacitors as removed, as you might be able to see the two on the left have a slight 'bulge' - they were the Atwo with the slightly different colour tops.

Below  is the ESR value for one of the axial capacitors removed from the board - as you can see not too bad with and ESR of 0.19 Ohms and 3473uF  but they will get changed anyway!

Here is the replacement capacitor an ESR of 0.06 Ohms and a capacitance of 3235uF.

Remember the bottom of the board - well after a little rework etc. this is what it turned out like :-

Not perfect but pretty good, I also cleaned and re-flowed the edge connectors, if you do this make sure that the re-flow is as thin as possible - or you might open up the edge connector in the chassis and cause intermittent problems. When I put any of the boards into the chassis I use the cleaning solution that I mentioned earlier to protect and ensure a good connection.

Finally here is the completed board :-

One final note - TAKE CARE with the insertion of the vertical capacitors !! - look at the above picture - this board is a little different - the capacitors are not all in the same orientation - check and re-check - as if you get this wrong it will not be pleasant !! - I also noted that the board itself has the orientation marked on the board - but you can't see them when you put the capacitors in - so checking is a bit difficult !! 

Yaesu FT-902DM "Restoration" Part Two

Hi,

After a little testing everything tested out pretty well, RX was sensitive and working well, all the controls worked nicely with no "scratchiness" at all or needing to "rock" switches to get them to work.

Anyone who restores or repairs older transceivers will recognise these problems ! - usually quite easy to fix with the appropriate specialised cleaners - Corrosion X - I first starting to use this when I noticed that the great Kenwood restoration guru Jim, KE7OAY used it - it is really very good!) put it in a dropper dispenser and it lasts for ever and DeOxit - I recommend not getting an aerosol but getting a dropper bottle or a 'pump action' bottle - a lot easier to user and doesn't 'spray' everywhere - wasting what is a very expensive liquid !

I'll use a combination of these on the switches and pots when I clean them up - I do when I'm restoring others equipment, as a preventative and restorative measure.

So after checking I decided to replace the bias and HT electrolytic's everything checked out OK after slowly bringing up the voltage (see previous post) but these components are over  30 years old so replacement with newer, better tolerance 105deg components with better voltage ratings where available will help to preserve the radio for another 30 years hopefully !!

So after taking precautions to make sure that the radio (and its electrolytics!!) were fully discharged and the transceiver not plugged into the mains - we begin......

So board PB1717 (Rectifier C Board) first -

Before Capacitor change

Having a really close look at this board - overall its in good condition. There was no real worries about the capacitors, although the middle capacitor on the lower row (you can just see it in this picture) did look a little discolored compared to the others, no sign of stress such as bulging sides or tops.

Other components looked in good condition, although as always with this age of Yaesu equipment (or at least the ones I've worked on) the components seem to have been inserted in the board by someone who wanted to get home early on a Friday afternoon, they are not vertical and overall pretty poorly placed.

You might think a little OCD (?) but actually vertical components help heat flow and aid reliability so I usually (very carefully!) align them.
  




So on to removing the capacitors. Yaesu put these capacitors in with a small amount of 'glue' around each one as the radio could be used mobile (!) and it was an attempt to stop vibration based failure.

My approach is to use my desolder station (a god send - if you regularly repair or restore get a decent one!) to remove the capacitors. I do one at a time and start with the big ones.

removed electrolytics

Not quite sure that the photograph (left) shows it but the capacitor on the right of the photo has a very slight 'bulge' on its base, the left hand one is flat, so perhaps just as well I took the trouble to power the transceiver up carefully and I'm replacing the capacitors !!

The white / yellow stuff is the glue that Yaesu used. The trick to getting the capacitors out of this stuff is to desolder the legs carefully from the PCB and check that the legs are free, and then carefully - very carefully gentle rock the capacitor back and forth - don't force it - you may crack or damage the PCB :( 




Just for 'fun' I thought i would check the ESR and capacitance using my Peak ESR+ tester (another great bit of kit!) - 

As you can see the ESR is .49 ohms and its capacity is just over 28uF - not too bad for a 30 + year old capacitor !!!

But I'm replacing it anyway.....

So here is a comparison to the replacement capacitor as you can see its value is pretty much spot on and the ESR is slightly better at .47ohms.

The more observant amongst you will notice also that it is a higher voltage rating - 400V rather than 350V.

If possible (without going mad) I like to up the voltage rating a little, and of course improve the temperature rating to +105deg - not sure what the original ones were but most probably +85deg. This will again help aid reliability and longevity


I wont bore you with lots of pictures of removed capacitors etc.

Remember to clean the 'glue' residue off the board before mounting the new capacitors, I use a combination of a PCB 'tooth' pick tool and a little PCB cleaner - works well.

The board has the polarity of the capacitors marked with + and - , so be sure to follow those correctly, if your thinking of doing this - you'll know that the white stripe (with the - marking!) points to the minus lead - this is also the shorter of the two leads (but don't always rely on that - sometime they are trimmed incorrectly!!)

So what was the result for the Rectifier C board ?

Finished board

Again the more observant will note that I haven't change the axial capacitor at the right of the board - simple reason is that I didn't have one in stock ! - I checked it using the peak ESR+ meter and its ESR and capacitance was fine so I decided to leave it. I've order some new ones and when they arrive I'll replace it.

On a final note - always use the best capacitors you can find, a brand name like Rubycon, Nichicon (which I try to use) etc. - others may disagree

A word of caution though - use a reputable supplier - they're are fakes out there and eBay is awash with 'good value' components. I only purchase through RS Components - they might be a little more expensive (in some cases they are a lot cheaper!) but the peace of mind is priceless - especially if your doing the work for someone else !!

Now onto the next board ........ 

Yaesu FT-902DM "Restoration" Part One

Hi,

I Often get offered equipment to repair directly, and as you know (if you read these occasional blogs!) I haunt eBay and few other forums looking for my favourite equipment, Heathkit, Drake, Collins as well as for interesting equipment that needs repair or as its known to most advertisers "Needs TLC" or "Untested - no power supply" - all of which general means - either "I've tried to repair it and I've failed" or "I've let somebody have a look at it and it came back worse than it left" or (very occasionally) people are genuine and absolutely truthful about the equipment or situation.  

We this one is an example of exactly the last one.

I was looking on one of the forums and noted a posting about an FT-902DM with Speaker unit, FC-902 ATU and a FTV-901R transverter. These were part of a silent key estate and the seller had been let down multiple times by people offering to buy and then not turning up or making an excuse. This advert said quite clearly that they had not been powered up as the seller was worried that they hadn't been used for sometime and he knew that to just 'turn them on' was a mistake (literally a big bang approach in many instances!) and he didn't have a Variac or such to do it properly so he'd left them.

Well that's a good start I thought - at least he cares and knows enough not to just turn them on. After some email exchanges and a few pictures - which showed them as in reasonably good physical shape but very dirty and unloved, I decided to purchase them. 

I've done many re-capping / restoration /  of Hybrid transceivers for other people and I have a modern 'Digital Variac' as well an 'old' style' one for just such purposes (often used for Drake and Collins kit!)  so I thought I'd give it a go for myself for a change.

True to form, I travelled to his QTH and met the gentleman selling them, he was honest as the day is long, the kit was exactly as he described and even had manuals for all the units - no interconnecting cables (but he had mentioned that) and also no rear AUX plug (remember with this or the right pins (1 and 2) being linked together the heaters wont work on the PA so no output). The 902DM did have the all important mains cable and plug though - this is good as they are increasingly hard to find and command quite huge amounts of money if they come up (£100+ !!!)

Anyway money exchanged hands and I was the proud owner of my own FT-902DM setup.

Here's some pictures of the lineup, not sure if it really comes across on the pictures how dirty and grimey they were, not the fault of the gentleman selling them I think but they way they were stored prior to him, in a garage would be my best guess.

 From the front looks good, dirty and grubby but no real marks on the from panel, all the controls work quite smoothly and the tuning dial at least moves (although you can't tell from the picture) but it did 'bind' a little on the rear skirt - possibly it had received a knock at some time - hope the VFO and the display works! - These are notorious for the counter chip going u/s - I've replaced a couple with a great kit from a Japanese amateur Teruhiko Hayashi ( JA2SVZ ) just google it if you need one.

As you can see from the picture right - this shows some of the grubbiness of the front panel / knobs etc. Nothing really to worry about on that front some ultrasonic cleaning should have them pretty much as good as new

The FC-902 looked good although as grimey and dusty as the others as well, all the knobs were there and they all moved fairly well the band switch moved with a satisfying 'clunk' - I've repaired one where this wasn't the case and it had caused arcing on the switch - it had lost one of it bearings and it caused the switch to have a very 'sloppy' action - possibly causing the issue. No such problem with this one :) 

Another picture showing how dirty it was

The FTV-901R transverter - again fairly dirty - this one was fitted with what I think was the standard 144Mhz plug in and no others

The other side of the unit

And finally the speaker unit - this isnt the right one for 902 range but was part of the lineup as it arrived. It has a white fascia edge and so is most likely an Ft-101 one. It also has a modified front panel with a fairly crude (and not central!) 3.5mm headphone socket. It is of the right impedance though and so is a worth keeping in my view - the right size etc.




So after introducing the kit - what next?

Well power it up of course !

As mentioned earlier if you have no idea of the provenance of the equipment - when it was last used or how its been stored - DO NOT JUST PLUG IT IN A TURN IT ON !!!

I would strongly recommend that you use a variac to slowly step up the voltage giving time at each step for the capacitors to re-form if needed, I would further recommend that when you have done this (I'll go through the steps I use in a moment) that you use a 'dim bulb tester' as well (not sure what one is then perhaps don't do this work - but if your interested then there a link here which explains what it is and who to build one.

I also power all my equipment via RCD breakers as well as test devices such as this radio.

I do this with all equipment - valve or otherwise - as its best to be careful.

So my regime is pretty much this (other will have their own which is no doubt better but this works for me).

1 - Check that the radio is configured correctly for the voltages (you'd be surprised how ofther this isn't the case!) - for this 902DM the case needs to be removed and the connections on the transformer checked - others might be different.

2 - When you have the case off - have a very careful look inside - look for damaged components - especially look at the capacitors in the PSU and bias areas - if need be remove casings or PCBs to do this (especially the case in hybrid radios like this one) - if there is no evidence of damage, overheating or capacitor stress (such as bulging or weeping) then move onto 3 - if in doubt don't power the radio - replace the capacitors. Also remember Capacitors can store charge for long time and so use a 'chicken stick' to discharge capacitors especially HT side if your unsure. here's a link to one if you don't know what one is here - again if you don't know about this - ask yourself should you really be doing this !! 

3 - Re-check number 1 and 2 - do this after a break (preferably the next day)  - remember these voltages can be lethal!

4 - Time to start applying voltages, I start at 25V then step to 50V, 75V, 100V, 150V, 175v, 200V and final 235V. I leave about 30 minutes at each stage, remember this is not a quick job - take your time. My electronic variac has a current meter as well - I would suggest you also have some method of checking current consumption. Don't forget to turn the radio on when you do this (!!!!)

5 - At each step watch carefully the current consumed and look and listen for any signs of stress with the radio or anything unusual such as smell etc. If current starts to rise quickly then stop - turn off and find the reason.

6 - When you finally get to the full mains voltage - leave it on and let it settle down for at least 90 mins.

7 - Finally remove the Variac (turn everything off first including the radio !) and then connect the dim bulb tester before you switch the radio on for the first time without a variac. Then switch the radio on - the dim bulb tester will glow brightly and then should settle down to a glow and the radio should power up. If the bulb stays bright you have a problem - the radio is drawing to much current - check whats causing it. 

8 - Finally start testing the unit and realignment etc. - and don't ever forget that there are lethal voltages in the radio - its bite might be fatal !

Finally a note of caution (and a disclaimer) - if you do work like this (and possibly follow my instructions) you do so at your own risk I will not be held liable in anyway whatsoever. I know what I'm doing and the risks - every radio is different - so proceed with great caution and at your own risk - if your not sure the don't do it and let someone who knows what their doing - do it !! remember these voltages can be lethal - its not 12V !!!

So if your got this far - well done - sorry for the disclaimers but these can be dangerous radios and I'd hate for anyone to hurt themselves.

After doing all that on the FT-902DM what happened ????

Well I'm pleased to say that it came up fine - no bangs or capacitor problems - display came up fine, meter bulbs and VFO backlight worked (!) - and audio from the speaker as well.

It tuned ok on all bands and peaked signals nicely on the pre-selector.

I will be replacing the HT and Bias electrolytics on the rectifier boards as the next step - in the meantime I will start testing and see what else needs doing. I may well recap the whole radio but the HT and bias are the most important - even if it did power up no problem after all my trouble to carefully step up the voltage - you never know though so take care !!

Overall a great result so far !!!

73s

Chris