Removing tuner modules Observe safety procedures (disconnect power) and antistatic handling precautions (wear cotton clothing and discharge static electricity). A desoldering station is recommended but it *is* possible to remove a tuner module with a VERY hot soldering iron and desolder braid ("Multicore desolder wick") as supplied in our solder kit. Full information is given in this book:-
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Removing the DRX100 tuner module
WARNING Do not attempt this operation with inadequate equipment or knowledge. Do not attempt this operation unless you are certain that the tuner is faulty Disconnect the receiver completely. To gain access to the tuner you must remove 5 cover screws and lift the cover off. Lift the power cord grommet out of the rear panel slot. Remove the tuner nut and washer, 3 rear panel screws and the tiny screw that holds the module inside to the rear panel. Unclip the rear panel at top corners and use a thin blade to release the three clips underneath. Pull the panel off. Now look at the main board. When you handle the main board, remember it is susceptible to damage from static electricity. Put your hand on the metal chassis before touching the board. Take care not to knock any components!
Early models had one screw hidden beneath the plug-in module at the rear. Simply pull the module upwards to remove it. Remove the 5 or 6 screws that secure the main board and lift the board just enough to let you get the desoldering iron under it to desolder the tuner pins so that gravity assists. Sometimes it will be necessary to add fresh solder to each pin before desoldering is possible.
Note: Although it may be possible to remove all traces of solder with desolder wick or a pump-action solder remover, I have personally never tried it. However, customers tell me that solder wick does work I use a DS-801 desoldering station, made by Weller, which cost about £500 in 1992. Other suitable stations may be available at slightly lower prices.
Turn the main board upside down. The pins are in plated-through holes with several tracks joining them on the top surface of the PCB (out of sight beneath the tuner). Put the soldering iron tip on each tuner pin and push it from side to side to ensure that it is free to move in the hole, with no solder connecting it to the track.
Remove some solder from both tuner fixing lugs so that you can untwist them. They must align perfectly with their slots. The success of the next operation depends on the way in which you hold the tuner and iron. You need a VERY hot iron. I use a 45 Watt Weller iron with a number "8" tip (430'C). Most "D.I.Y." irons do not produce enough heat so you may need an assistant to hold a second iron. Place your left thumb on the threaded 'F' connector and press down while, at the same time, pushing up against the board with your first finger. Hold the iron in your right hand. Press the soldering iron tip against the tuner lug and apply fresh solder between them to improve heat transfer. As the solder around the lug melts, maintain the gentle pressure with finger and thumb. When you feel the solder release its grip, ease the tuner lug out of the slot until it is just clear. Now repeat the operation for the other tuner lug. Make sure that the tracks which connect to the tuner pin holes on top of the board are undamaged. If any are damaged, repair with very fine wire and measure the continuity. Fit the replacement tuner carefully and solder the lugs first. If you solder a pin first, any movement can break the delicate tracks on top of the board. Check all plug-in connections - especially the white connector near the front panel. Make sure these plugs are pushed fully into their sockets, otherwise you may find the receiver is "stuck in standby". Now reassemble the receiver, ensuring that all screws are fitted into the correct holes and tightened. Reconnect all cables and apply mains power. If the receiver still gives "No Signal" indication after one minute warm-up then you damaged a connection or the initial diagnosis was incorrect. (The "No Signal" message can have other causes).
Protection Tuners use electronic components that can be damaged by static electricity. The damage will be invisible. To minimise the risk of damage, please avoid wearing synthetic clothing which can generate electricity - cotton is best. Disconnect 230v power from the receiver. Keep the tuner module in an antistatic bag, if available, or in aluminium foil. Safety Although the DRX100 bears the "BEAB approved" mark, there's a couple of features relating to safety which, in my opinion, may have crept into the design after approval was granted. The first is obvious in that, in later DRX models, the mains cable insulation has been removed so that a ferrite ring could be fitted. This modification has not been carried out on all versions - I've seen receivers without it - but, where it has been done, it leaves the brown and blue mains wires free to touch the cover. I recommend that you put insulation over these wires before reassembling the receiver. The second point compounds the first in that the mains protective earth is connected to chassis by means of a single screw (see red arrow) that holds a printed circuit board soldered copper pad in contact with the metal base. The last time I read a safety standard from BSI it stated that the fixing method for the protective earth wire should not be dual-purpose. This requirement stemmed from the days when a mains transformer was bolted to a chassis and one of the bolts also held the earth tag. If someone swapped the transformer they could accidentally leave the screw loose. In fact the screw might work loose simply through the vibration of the transformer, leaving the equipment without a secure earth connection. So the protective earth connection should always be fixed separately, using a method that can not accidentally work loose.
	In the case of the DRX100, the same screw is used to hold the power supply board AND to hold the copper pad in contact with the chassis. If someone removes the power supply and fails to replace and retighten the screw, that might leave no reliable earth connection. In addition, the solder on the copper pad is quite thick and may "creep", leaving the connection loose. Finally, there is no locking washer or nut. Of course, a bad earth connection will show up in an earth continuity check, as any workshop technician knows - but how many of us carry out this test on every unit we repair? I recommend, as a minimum, that you fit a locking washer under the screw head.