FT225RD
SM7OVK-Maintenance


Introduction

The FT225 has been around for several years now. I'm actually not sure when the first examples were put on the market, but it was probably around 1977.
FT225 was a "development" from the FT220 and FT221 types with some improvements. The FT220 had real helix-filters on the RF-input and the local-oscillator was also filtered with a helix. This was removed in the later FT221 and FT225 models, probably to reduce cost, (?).
FT225 was made in two types, one with analogue scale, FT225R, and one with digital readout, FT225RD. There was also a memory-unit available, but it's quite rare.
The idea with this page is to encourage other hams to do some maintenance on their FT225's. In this way the FT225 will still be around for some more years and continue to put good quality signals on the band!

Maintenance

There are basically two different types of maintenance, preventive and corrective.
Preventive maintenance is something we do before any faults are detected while corrective maintenance is something we do when a fault is detected.
This page starts with corrective maintenance and later preventive. The last part contains some hints about adjustment. Adjustments are a way of preventive maintenance since this often must be done when the electric components get older and they no longer can keep their specifications. Please let me know about your thoughts and if you don't find what you're looking for! (Please always put FT225RD in the email-subject!)

Lamps

There are not many lamps in the FT225RD actually only three. I didn't care when my two lamps above the VFO-dial didn't light anymore, but when G3TDM - Roger, asked me he triggered the thought. (The third lamp is found inside the S-meter.)
I don't know the exact specification for these lamps, but I found a lamp that is 4.25mm in diameter and 12mm long and using 14V/80mA, (a great portion of the total powerconsumption in receive-mode - nearly 7%!). In Sweden these lamps are found at ELFA number 33-538-36 at about a dollar each. (If you have problems to find the lamps - let me know and I'm sure we can work something out.) The dimensions are not as important as indicated above!
I'm sure there are hundreds of types that could be used, but lamps are not common anymore and my first attempt was to use green LEDs, but this didn't work - the light is too weak. (I have not tested with blue LEDs, but this could be an idea-?)
Remove the top cover. To locate the lamps one have to remove the COUNTER UNIT. This unit is mounted with four screws and located right behind the LED digits - the unit actually holds the digits. Unscrew the four screws and carefully lift the unit. Under the unit there is a cable connector, disconnect this connector. Now it's possible to remove the unit from the radio. The two lamps illuminating the analogue VFO-scale are located beneath the counter unit.
The lamps are mounted inside some rubber-holders and carefully lift them out of place. Cut the wires close to the lamps - only one lamp at a time! (So you do not mix the wires...if you do, it's no problem to turn the FT225RD on without the counter unit, BUT be careful the lamp-wires carries 13.6V and a short-circuit will certainly blow the fuse!) Remove the lamp from the rubber-holder and fit the new lamp.
Cut a total of four short pieces of crimp-isolation, about 7-10mm long. Put one piece of isolation on every wire before you solder the wires to the lamp. Repeat this with the other lamp. Heat the crimp-isolation and refit the rubber-holders now containing the lamps.
Finally mount the counter unit and do not forget to fit the connector! (Total time for this "project" is about half an hour.)

Capacitors

Electrolytic capacitors dry out and if they are placed in a hot environment this process goes even faster. If the capacitor gets dry the capacitance will be lower, and after some time it will be close to 0. I have measured the capacitance on some of the capacitors that I have exchanged and the capacitance was sometimes down at about half of what the capacitors was marked with, some capacitors would work better as a resistor! It has been shown that a decrease in capacitor working-temperature of ten degrees would double the lifetime!
The only way is to exchange the capacitors and my recommendation is to exchange all capacitors! This takes time off course, but it's certainly worth the time and money! My suggestion is to make a paper-copy of the FT225-schematic and whenever you replace a capacitor - mark this on the special schematic-copy! In this way you will be sure to exchange all capacitors. (One doesn't have to exchange all capacitors at one occasion and do notice that all values are not right in the schematic.)
Electrolytic-capacitors are most often marked with either 85 degrees or 105 degrees, (there are 125 degree types as well but these are not commonly available). Try only to use the 105-type since this will increase lifetime. Always use capacitors that can handle voltages with a factor of 1,5 to 2 times the maximum voltage present at the capacitor. It isn't any advantage to increase this factor more since this can result in a capacitor with higher internal resistance and this will slow down the capacitor.
It's important to get new capacitors of good quality, do not use old capacitors from your junk-box they could be older than the capacitors you're about to exchange! Also beware of cheap stores with large quantities of capacitors where you can by 100 to the price of one at a normal store - there is a reason for this low price. Transistors, diodes etc survive but electrolytic capacitors dry out if not stored properly.
When exchanging the capacitors also pay attention to the voltage-regulators. Many of them have originally too large capacitors close to them. Normal voltage-regulators, as the 78XX-types, must have small capacitors mounted close, 0,1-1uF, to prevent oscillations. Close in this case is about 10mm from the voltage regulator, ie often soldered directly on the regulator.
Tantal-capacitors most often have longer life than electrolytic capacitors and they can often replace electrolytic capacitors with same or better result.
These small tips will increase the capacitor-life and therefore also the life of your FT225. I would like to point out that normally no adjustments are needed after exchanging an electrolytic capacitor, but be careful when you are inside the FT225 and soldering!

Transformer

The built in transformer can cope with many different supply-voltages. My FT225 was winded to 220V, (2 times 110V), but when Sweden changed to 230V many years ago I changed the transformer to 234V, (2 times 117V). This means that the output voltage from the transformer is lower and this will save some power in the voltage regulators, ie lower temperature. The lower voltage will spare the large capacitor as well, (my large supply-capacitor is marked 25V and this is very close to the actual voltage present).
Don't be thrilled to think that the higher voltage will get more power out, it could probably - but so little that it's not worth it compared to longer life of your FT225! Remember that the rule of thumb says that double the distance mean that one has to increase the power four times, you can read more about this here.
NB! Be careful when playing around with the AC-voltages since this can be very dangerous! The supply is not turned of if the power-switch is in off-position! The only way to be 100% sure is to disconnect the power cord!

Silicon components

Some of the used components in the FT225RD are not manufactured any longer, or substituted by other types. This list is the first beginning and it's not completed. I will put new substitutions when I run into problems, or if you have any suggestions on component replacements that you have found!

original - replacement
uPC14305 7805
uPC14308 7808
uPC1008C MC4044

Adjustments

Please notice that some adjustments need proper instruments and/or special skills. Do not try to adjust your transceiver if you do not have these special tools! I can't be held responsible for Your mistakes and You are doing these adjustments on Your own risk!

The adjustments are divided into groups each marked with a number of + and *. These marks should be read as follows;

  • * = easy with no instruments
  • ** = can be done with no RF-instruments, but a receiver or DVM.
  • *** = can maybe be done with no RF-instruments, but a receiver, DVM, oscilloscope.
  • + = easy with some basic RF-instruments as powermeter or spectrum analyser
  • ++ = must have some basic RF-instruments as powermeter, spectrum analyser, frequency counter
  • +++ = must have good RF-lab
  • ++++ = only RF-pro
Carrier balance + **

(To do this adjustment you will need a SSB-receiver(**) or a spectrumanalyser(+).)
Let the FT225 run for an hour or so, it must be warm. Remove the top cover, do not remove the top cover earlier since the circuits should keep the same temperature as later when you operate - preferable with the cover on. (Unfortunately there is no temperature-compensation on the circuit.)
Turn down the SSB MIC GAIN to minimum, or even remove the microphone. Connect the transmitter to a dummyload. Put the FT225 in USB-mode. The SSB-receiver or spectrum analyser could be connected to the transmitter-output if you have a proper coupler, if not just wrap some cable around the connection between the FT225 and the dummyload. With PTT "on" one should see, or hear, a tone. Adjust VR505 and TC504 on the MIC AMP UNIT to minimize this carrier level on the transmitter output.
Yeasu writes in the manual that this should also be done for LSB , skip this since only USB is used! This will give nearly 20dB better suppression than if one tries to get "good" suppression on both LSB and USB.
I have changed the resistors R43, R44 and R45 to metallic-film resistors with the same values as earlier, (100 ohm). The reason for this is that this type has a very much lower temperature-coefficient, (50PPM compared to several houndred PPM with the original carbon resistors), and the drift will then be lower.
When you have adjusted the carrier balance let the FT225 run for an hour and check again, adjust again if necessary.

Frequency adjustment ++

(To do this adjustment you need a frequency counter and a probe.)
Let the FT225 and the frequency counter to warm up, this is very important! The FT225 must be running for about 1 hour before any measurements are done, and this is normally also the case for the frequency counter.
Turn the AC-power of, it is safest to remove the AC-cable. Remove top and bottom cover. With the FT225 upside down, find connector J13 and identify pin33, ie A17. Connect a frequency-counter with a short piece of coaxial cable to this pin. Put the FT225 in USB-mode and the 144MHz range. (The VFO-dial doesn't matter.)
Turn on the FT225 but be careful - the AC voltage is present at the fuse and transformer even if the radio is turned off on the main-switch!
The readout on the frequency counter should be 125.1000MHz. If the readout isn't stable, disconnect the short coax from J13-A17 to J14-8. (J14 is the PLL-UNIT - don't be worry the PLL will not lock and the display on the FT225RD will turn off.)
The readout must be "rock steady"! (The measured output is from a crystal oscillator.)
With the L801 the oscillator can be adjusted. When the oscillator is properly adjusted to 125.1000MHz let the unit run for half an hour to see if it's really stable. If you do not have an extensionboard, turn of the FT225 and remove the LOCAL UNIT. Adjust the L801, put the LOCAL UNIT into place and turn the FT225 on. If you adjust the inductor clockwise the frequency will decrease, counter clockwise it will increase. Repeat this procedure until 125.1000MHz is read on the frequency counter.
Now, connect the frequency counter to J12 pin 5, (I prefer to use an oscilloscope-probe in this measurement since it will not load the oscillator output).
With the FT225 in USB-mode and the clarifier off, adjust the VFO-knob until 8200.00kHz is measured on the frequency counter. (It doesn't matter what the FT225-display is reading!)
Locate the OSC UNIT, the unit is found right behind the S-meter and there are four variable capacitors on top marked LSB, USB, CW and FM. (The OSC UNIT schematic is only present in the manual on page 25.)
Adjust the TC1702, (the numbering in the manual is wrong!), on the OSC UNIT until the readout on the FT225-display reads 143.9985MHz. DO NOT TOUCH THE VFO-KNOB DURING, OR AFTER, THIS ADJUSTMENT! (The TC1702 is marked with USB on the OSC UNIT.)
Check that the readout is really stable. It will not be as stable as the 125.1000MHz measured earlier. Control the 8200.00kHz on the frequency counter and check if the readout on the FT225 is sliding.
Without touching the VFO, change into CW mode and adjust TC1703 until 143.9993MHz is read on the FT225-display. Repeat this procedure with LSB, 144.0015MHz, and FM, 144.0000MHz. AM and FM should have the same readout.
Let the FT225 run for some time, 10-15 minutes, and check the 8200.00kHz on the frequency counter. Observe if the FT225 is as stable as before the adjustments. Do also check that the FT225 display do not alter when the frequency counter is disconnected. If it does, the oscillator has been to heavily loaded and the procedure should be repeated with a small capacitor between the counter and the FT225.

Optimise original front-end + *

The original front-end has four trimmer-capacitors. Two are used in the input filtering and the other two for the pre-mixer filter. If you have removed the cap-diodes in the front-end and replaced them with fixed capacitors - or if you just want to check the sensitivity of the receiver, you must adjust these two filters.
Remove the top cover and locate the front-end PCB, "RX RF UNIT PB-1746". The trimmers are numbered TC101, TC102, TC103 and TC104. The first trimmer is "special", or at least it needs a special trimming tool. The only speciality of this trimming tool is that it must be much longer than for the other three trimmers. I used a normal Spectrol tool and modified it by cutting off some plastic with a knife to get down to the trimmer. When this is done this tool could be used for all four trimmers.
Set the VFO for some beacon, or if you have a signal generator put a not to strong signal into the FT225. About -110dBm is appropriate, but there could be advantages with a beacon signal since you then match the filters to the rest of your system - with a signal-generator you match the input to 50ohm.
First adjust the TC101 and after this the TC102. Repeat this procedure two times and adjust for maximum signal. Then try with TC103 and TC104. Repeat the procedure two times. Now repeat the TC101 and TC102 procedure. Do this until you are sure that there is nothing more to get...


To be continued...


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