Amateur Radio Station WD8RIF | Troubleshooting QRP Plus

With the cover off, the RF board is exposed at the top of the radio. It has 4 RCA plug connectors plus a number of useful test points.

BFO cable	This is next to the right side of the wide ribbon connector at the front of the PCB. You can check the BFO frequency and output level by pulling the plug out and connecting to a frequency counter or oscilloscope. In each case it should see a 50 ohm termination.
output level	0.63 Vpp or 0 dbm for the upgrade version 0.80 Vpp or so for earlier ones
frequency	The frequency needs to match the marked value shown on the RF (and LO) board. i.e. if the board has a label marked 0550 that means the Xtal filter center freq. is 50.000550 MHz. The BFO freq. should be 200 to 400 Hz higher in RX. Turn the power level to zero and key the radio. The freq. should shift down 700 Hz. The key-up and key-down frequency is programmed into the EPROM when calibrating the radio.
RX antenna cable	This is on the left side toward the back of the PCB. An antenna can be connected directly to this point using a suitable RCA adapter. This will bypass the TX board relay and the panel board attenuator. This may be helpful in locating problems with them or the connecting cables if the received signal is weak or missing.
RF output connector	This is on the left side of the wide ribbon connector at the front of the PCB. RF drive to the transmitter board exits the RF board here. The output frequency is the operating frequency and the output level is nominally 40 mW. ( 3 to 4.5 Vpp into 50 ohms). There will be considerable harmonic content especially on the lower bands here. When disconnected the ALC attempts to maximize the output. The ALC voltage will go to about 4.0 volts at the junction of R5, 10k and R6, 47k. (just in front of the MC1350, U1) The ALC voltage is 6.5 during RX and will go to about 5.5 volts with 5 watts output from the TX board. Pre-upgrade radios have similar RF levels but ALC controls the audio gain for SSB only.
LO Cable	This is at the rear edge of the PCB next to the mixer. The local oscillator should supply 13 to 15 dBm (3-4 Vpp) to a 50 ohm load. The frequency will be 50 MHZ minus the operating freq below 10 MHz or 50 MHz plus the operating freq above 10 MHz. i.e. when tuned to 14.060 MHz the LO output is 64.060 MHz. Pre-upgrade radios have about 7-10 dBm output (1.5-2Vpp).
Main power input	Power to the RF board can be measured at the ribbon connector at the right side. The upper 3 pins are tied together. The supply is nominally 10 volts for the upgrade radio and comes from a regulator on the AF board. Earlier models have 12-13.8 volts supplied from the rear power jack via the TX board --> AF board --> 26p ribbon cable.
T/R power switching	Two circuit traces pass though the open center area of the upgrade RF board usually going under the stick-on label. The left one is powered during transmit and the right one during receive. Each voltage is about 10 V and only one is active at a time. The switching circuitry is just behind the wide ribbon connector. Similar circuitry on the pre-upgrade is in front of the RF board relay. Tx activates 12.5 V at the left end of R37. There is 12.5 V at the front end of C57 during RX.
AGC voltage	You can measure the AGC voltage at the front end of R28, 47k(27k on early upgrade radios). For pre-upgrade radios the AGC voltage is available at the rear end of R10, 27k. Be careful not to short this point to the nearby ground trace. With no signal the AGC voltage should drop to less than 3 volts. Upgrade radios have about 6.5 volts with an S9 signal. Pre-upgrade radios are higher at about 7 volts.
Sythesizer control loop voltage	This voltage can be reached from the right side of the LO board (third one down). R22, 1K is just in front of the rear spacer. The rear end is a good spot to check the VCO control voltage. It will always be between 3 and 6.5 volts depending on band and frequency. If the loop loses lock the voltage will be either 0 or 8.5 volts, the limits of the supply. All radios should meet this test.

RX distortion or TX instability	Feedback due to speaker cable routing. It should lie behind the panel board not on top of the RF board. The speaker terminals should face forward.
No display, radio appears dead	After checking the fuse look for a loose ribbon cable between the LO and panel boards. This short 10 pin cable sits on top of the S-meter. It may work off of the panel board in some cases from shipping and handling. It can be pushed up into place with a pocket screwdriver. Make sure the meter terminals clear the cable.
At turn-on the display shows 50 Mhz or 7.999 MHz and memories are lost.	The battery is dead or possibly loose. It can be replaced without removing boards. Do not grab it with needle nose or forceps. You will short it out. Use two small screwdrivers or better yet something non-conducting. Note the plus side is up--you can check the battery voltage easily. Be careful not to bend the clip. The contact will be loose later.
Frequency error	Don't forget that the displayed frequency shifts 700Hz depending on the CW/SSB mode. Push bandwidth then fast buttons to toggle the mode. Nothing else happens when you do this.
No TX	You may be tuned out of the ham band for TX. This can happen when using RIT. It is possible to tune the receiver anywhere using RIT. If you started out of the ham band nothing will happen on TX. It is also possible to be listening a long way from where you ARE transmitting.
Radio goes into transmit mode or acts erratically when mic or key plugs are inserted	Check that the AF board is pushed fully back so that the jacks are flush with the rear panel. If the radio has been worked on, it may not have been pushed back before tightening the screws or the screws may be loose. Be sure the power cable is not trapped behind the PCB.
Weak RX signals	Attenuator in wrong position.