This page is prepared to help in troubleshooting a malfunctioning Vanguard Wepix-2000-B receiver. It does not include all the possible problems that can occur What it does show is that if it passes the following tests the receiver is in all probability OK and you should look for problems in the antenna, pre amp and lead-in cable.
The antenna does not have to be connected at this point.
1. Turn the receiver ON. Is one of the red LED's on the front panel channel indicator on? If yes go to step #2. If no, check the following:
Make sure the wall plug power adapter is plugged into a wall socket or extension cord. Check if the DC connector plug from the adapter is plugged into the DC receptacle on the rear panel of the receiver. Check if the panel mounted fuse is OK. A voltmeter is helpful.
2. Put the toggle switch marked SCANNING in the AUTO position and the SQUELCH control fully #3. If no, read the following:
If the LED's are scanning but not in sequence you may have a broken wire or a short on in counter circuit which consists of the 74LS191 mounted on the main board or the 74LS145 LED driver board mounted on the front panel and not visible. For this problem, which is very rare, it's best to return the receiver to Vanguard for repair.
If one LED is lit but there is no scanning the clock circuit may be out. Check or replace the NE555 on the main board.
3. Put the SCANNING toggle switch in MANUAL and press the push button switch in hold it in for a second and release it . Each time you do this the channel indicator should advance to the next LED. If it doesn't, either a wire from that switch is broken or the clock circuit is not working. See above paragraph.
4. This step checks the SQUELCH and audio circuits. Turn the volume up midway. You should hear a fairly loud rushing noise. Turn the SQUELCH control slowly clockwise. At about midpoint the noise should suddenly stop. If it doesn't something is wrong in the squelch circuit. That could be in the SL6601C, a broken wire or a failed component. It could also be that the receiver needs alignment. Since the squelch is noise operated, low sensitivity will produce low noise, preventing the squelch from operating. In this case it's best to return the receiver for service.
5. If the receiver passes all the preceding steps make this one final test. Remove the bottom cover and check the red LED mounted on the main board directly behind the channel switch. It should NOT remain ON. It should only blink when scanning. If it stays ON the synthesizer is out-of-lock, the frequency will be off and you will not be able to receive a satellite signal or it will be distorted. The cure for this can sometimes be simple. The VCO (voltage controlled oscillator) needs to be adjusted to compensate for aging components.
Remove the 2 screws holding the square VCO cover. You will see 2 coils and 2 trimmer capacitors. You will adjust ONLY the one trimmer capacitor closest to the front panel. It adjusts the VCO center frequency. Put the SCANNING in MANUAL and start at the lowest frequency. Take a tuning tool or small screwdriver and very slowly turn it clockwise or counter clockwise for about 1/4 turn. Somewhere in that range the LED should go out.
The synthesizer is now locked at that frequency but you want to make sure it stays locked on all frequencies so use the push button to go to the highest frequency and reset the trimmer if necessary, until the LED goes out. Use the push button to go through the entire range of frequencies and check that the LED doesn't stay ON at any frequency. It's OK for it to blink. Replace the VCO cover being careful that it is straight and do not tighten the 2 screws excessively or you will collapse the cover.
We are currently working on completing the schematics which will be in sections. Each section will be placed on our web site as they become available Check our site weekly.
VANGUARD ELECTRONIC LABS