Revox-G36-tape-sm1 维修电路原理图.pdf

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1、 RadioFans.CN 收音机爱 好者资料库Contents 1 General 3 2 Mechanical Description 3 2.1 Mechanical checks and adjustments 4 2.1.1 Tape path 5 2.1.2 Brakes 5 2.1.3 Tape tension 7 2.1.4 Pinch roller 8 2.1.5 End of tape switch 8 2.1.6 Wow and flutter 9 2.1.7 Tape speed 10 2.2 Routine maintenance 10 2.2.1 Cleaning

2、10 2.2.2 Lubrication 10 2.2.3 Servicing of solenoids 11 2.2.4 Servicing of push button assembly 11 2.3 Removal of capstan assembly 11 3 Electronic Description 13 3.1 Circuit checks and adjustments 13 3.1.1 Measuring instruments 13 3.1.2 De-magnetising 14 3.1.3 Head alignment 14 3.1.4 Playback amplif

3、ier 16 3.1.5 Bias adjustment 17 3.1.6 Measurement of overall frequency response 18 3.1.7 VU-Meter adjustment 19 3.1.8 Adjustment of head shielding 20 3.1.9 Channel to channel crosstalk 20 3.2 Tuning the bias traps 21 4 Troubleshooting 22 4.1 Mechanical troubleshooting 22 4.2 Electronic troubleshooti

4、ng 23 5 Technical Data 24 6 Circuit Diagram 26 7 SPARE PARTS LIST - ISSUE IV 39 RadioFans.CN 收音机爱 好者资料库1 General The REVOX Series 36 has been constantly improved and kept up to date, since it was first introduced in 1956. However, the present G still bears the same basic layout and conception as did

5、 the original A recorder. Compared with the preceding models, the following major innovations have been incorporated in the REVOX G 36 recorder : Hysteresis-Synchronous Capstan motor, VU-meters for record level control and a tape-tension switch to permit the use of all reels from 7 inch up to 10 1/2

6、 inch diameter. The G 36 model is available in both 2 and 4 track versions. Identification is made by the appropriate number being stamped on the head mounting plate, and on the upper side of the lower chassis. The recorder consists of an upper and lower chassis. These are joined at the rear by mean

7、s of the back panel which carries the input and output sockets, mains voltage adjuster and fuse-holder, and at the front by means of the loudspeaker panel mountings. The upper chassis carries the tape transport mechanism and the lower chassis bears the power supply unit and the electronics. All Audi

8、o Connections are led to standard phono sockets. To interconnect the REVOX recorder with other Audio Equipment, a selection of adapter cables is available. 2 Mechanical Description The machine employs three motors. Two are identical and perform the wind and tension functions. The third motor is larg

9、e and drives the capstan. It is of the pole switching variety and speed change is therefore effected electrically. The wind motors are designed to provide pulse free torque. Back tension is applied by electrical counter torque during the record and playback functions as well as during wind. The Caps

10、tan Motor is of the Hysteresis-Synchronous type, incorporating a special design feature to prevent hunting. By switching to either the 6 or 12 pole stator winding, the tape speed of 7 1/2 or 3 3/4 ips may be selected. The capstan drive, the pinch roller assembly and the headblock with the tape guide

11、s are carried on one die-cast frame. This ensures accurately parallel and permanent alignment of all major transport elements. The coupling between motor and flywheel consists of special silicone-rubber strips, with the whole assembly acting as a mechanical filter. A direct slip free drive is thus a

12、chieved whilst maintaining negligible wow and flutter. The pinch roller is held against the capstan during record and replay functions with considerable pressure. This necessitates the use of a capstan bearing designed specifically to withstand considerable side pressure for long periods. The pinch

13、roller arm carries the shield for the playback-head and the tape-lift mechanism for the rewind function. The brakes are mechanical in nature but are electrically operated. This is achieved by the action of the brake solenoid which pulls the brakes off during all operating functions. When the stop bu

14、tton is pressed however, or when the current fails for any reason, the solenoid is de-energized, and the brakes automatically come on, with the higher braking force always on the trailing spindle. All functions are controlled by the push buttons. Arcing damage and noise is prevented by the use of di

15、odes and RC networks. A sensing lever on the RH tape guide (3 in fig. 1 and 8) operates a switch (SE on schematic) which, in series with the stop button, provides a current path to a solenoid incorporated in the push button unit. This has the effect of clearing any selected function either by depres

16、sing the stop button or operation of the end of tape switch. On recorders up to serial No. 36 500, the function of the end of tape switch is delayed by about two seconds to avoid tripping during the start mode. On machines with higher serial numbers (recognizable by the end-of-tape switch being made

17、 of gold-plated wire with NC contact configuration) this time delay (relais) has been utilized to supply increased operating voltage to the wind motors, thus providing the required starting torque. (Inset schematic B and diagram 7.736.001-002:6 refer.) The tape guide pins to the left and right hand

18、side of the loading slot assist in achieving uniform tape tension due to the change in friction with varying wrap-around from large to small spooling diameters. A three digit tape counter is driven from the take-up turntable by a rubber belt. The translucent resetting knob of the counter is lit by a

19、 small pilot bulb which acts as a mains indicator. A remote control facility is provided Removal of the shorting link from the socket on the rear panel and the insertion of the correct accessory plug, lead and switch, enables the recorder to be started or stopped in either the record or playback fun

20、ction as selected. Operation of the remote control switch has the effect of de-energizing both the capstan and brake solenoids. ATTENTION If no remote control is used, the dummy plug must be inserted into the socket, otherwise the recorder will not start. 2.1 Mechanical checks and adjustments It is

21、advisable to use a full and an empty 10 1/2 inch spool when carrying out adjustments. For the majority of tape transport checks, it is essential to keep the plastic top cover in position. For other mechanical adjustments the top and head covers should be removed. To remove the plastic top plate, pul

22、l off the grey control knobs, the transparent selector discs and the plastic cover over the pinch-roller arm. Further undo the mounting screws (1 in fig. 2) of both turntables, of the head cover and the mounting lugs (2 in fig. 1) of the pinch-roller cover. When reassembling, take great care in tigh

23、tening the turntable screws uniformly to prevent them from wobbling. For best results, they may have to be rotated by 120. 2.1.1 Tape path The tape path level is determined by the left and right hand tape guides (3 in fig. 1) and by a small guide (4) positioned between the playback head and the caps

24、tan. We do not recommend that these guides should be interfered with in any way. Adjustment to the spool carrier height can of course be made to enable the tape to be wound centrally between the spool flanges. This is brought about by sliding shim-washers of varying thickness onto the spooling motor

25、 shafts after removal of the bakelite brake drums. To pull a brake drum off the shaft, screws should be inserted into the three tapped holes (1 in fig. 2) so as to serve as “handles”. Care should be taken to prevent damage of the brake bands at this stage. Where a brake drum has to be removed it is

26、recommended that the brake band be removed first. 2.1.2 Brakes The layout of the brake system is shown in fig. 2. The mounting bracket (5 in fig. 2) on the rear end (stationary) of the brake band must be held tight against the vertical pin on the chassis by sufficient tension of the leaf-spring on t

27、he bracket. It is important to check that the brake band (6) is running flat on the brake lining and not biting on the upper or lower edge. Adjust alignment of brake band by slightly pivoting it in the rivets if required. Correct tension for spring 7 is obtained when 160-220 grams applied as a tange

28、nt force to a 10 cm diam (spool and tape) causes the spool to move. See fig. 3. Brake tension may be altered by resetting the brake return spring (7) into any of the three holes on the end-brackets (5 and 9). The brake release solenoid must cause sufficient movement (approx. 3 mm) of the front-end b

29、racket (9) to fully free the brake band from the lining. Depress the “stop” and “play” buttons simultaneously to energize the brake release solenoid. If the movement is incorrect, loosen the nuts (10) and re-position the solenoid. The front-end brackets of the brake bands may be bent to achieve simu

30、ltaneous release of both brakes. The brakes should be kept clean and dry. Do not use any oil or grease on the linings. 2.1.3 Tape tension Back tension is applied by the combination of reverse direction torque from the feed motor and the degree of wrap around on the LH guide pin. Wear on the mechanic

31、al parts of the recorder will not alter the amount of tape tension. Any effects that could be attributed to inaccurate tape tension may be caused by: a. Faulty adjustment of the brake band b. Electrical fault in feed motor c. Electrical fault in phase shift-condenser (C 72 pos. 22 in fig. 5 and 6).

32、2.1.4 Pinch roller The pressure of the pinch roller can be measured by a gauge fixed to the pinch roller arm as close as possible to the spindle of the pinch roller (fig. 4). A constant tone tape should be played and the pinch roller withdrawn by the gauge until the note is heard to change. A readin

33、g in the region of 1.7 kg should be obtained. Adjustment to this value can usually be obtained by turning nut no 13 in fig. 5. Should this not provide the necessary amount of correction it is advisable to check the position of the solenoid no 11 in fig. 5 which will be correct when there is approx.

34、0.5 mm clearance at point A (fig. 5) with the solenoid energized. It is essential that the solenoids-slug fully bottoms in the energized position and when properly adjusted, there should be no movement of the slug when lifting the pinch roller off the capstan. Correct setting can be obtained by loos

35、ening the nuts (12 in fig. 6) and moving the solenoid in the required direction. 2.1.5 End of tape switch A. Photoelectric end-of-tape-switch Recorders with serial numbers from 58 000 onwards are equipped with a light sensitive auto shut-off device. It consists of a light source (Osram 3644), the ph

36、otoresistor ORP 62 and a printed circuit section containing two transistors (see fig. 1). The photoconductive cell is housed in the tape guide pin on the right hand side of the recorder. It has a dark resistance of greater than 100 k and this value drops to below 3300 under illumination. The associa

37、ted current amplifier energizes the push button release solenoid when light reaches the photoconductor. For normal operation of the recorder the sensing element is at its high dark resistance and both transistors are biased into cut-off. Illumination of the photo-resistor changes the bias condition

38、on T1 thereby raising its collector current. A voltage drop develops across the solenoid winding and T2 begins to conduct. Since T2 opens a current path parallel to the photoconductor, positive feed back action sets in which causes the collector current of T1 to rise quickly into saturation. To de-e

39、nergize the solenoid and to restore the nonconducting condition, the supply voltage has to be interrupted. B. Mechanical end-of-tape switch. This switch and its associate operating levers must be thoroughly clean to function correctly. On G-36 recorders up to serial number 36 500, the tape sensing l

40、ever operates a snap-action switch (SE schematic A) which is closed with tape tension applied. The right position of the switch assembly is essential for correct operation to be obtained. This adjustment is carried out by slackening the fixing screws and moving the switch bodily until the snap-actio

41、n switch closes when the sensing lever still protrudes by 0.5 to 1 mm from the outer diameter of the tape guide. On recorders with serial number 36 500 and up, the sensing lever operates a gold- plated wire contact. This switch opens when tape tension is applied (see BE in schematic Band 7.736.001-0

42、02). Adjustment should be carried out analogue to the above specifications for the snap-action switch by bending the long wire loop. In the resting position sufficient contact pressure should be available to make the short wire loop move beyond the point of contact by approx. 0.5 mm. This is achieve

43、d by bending the contact wires while operating the tape sensing lever by hand. The end-of-tape switch and its operating lever are then properly adjusted when the switch remains open (or closed on older models) for any movement of the sensing lever inside the tape-guide post. Accidental tripping due

44、to sticky splices etc. will thus be avoided. 2.1.6 Wow and flutter Accurate and useful measurement of wow and flutter can only be made with an appropriate instrument. The recorder is calibrated using the EMT Model 420. Possible causes of flutter may well lie with the capstan, capstan motor. Wow can

45、usually be seen as associated with the pinch roller speed and in some cases a faulty pinch roller may be the cause, and in others too much back tension or insufficient pinch roller pressure. For all wow and flutter investigations the transport mechanism must be completely clean. 2.1.7 Tape speed Tap

46、e speeds can be checked by running a marked, measured length of tape through the recorder. For a 100 sec. run 950cm would be required at 3 3/4 ips and 1905 cm at 7 1/2 ips. The difference in running time in seconds will be the speed variance as a percentage. Some variance can be expected with temper

47、ature increase but this should lie within the quoted tolerance. In very cold weather it may be noted that the recorder runs accurately at 3 3/4 ips but slows down when switched to 7 1/2 ips. This is due to drag from the cold grease in the capstan bearing, especially when new. After a short time of o

48、peration at 3 3/4 the machine should be capable of running at 7 1/2 ips. When detecting any deviations from the figures quoted, an accurate reading of the mains frequency should be taken first before investigating pinch-roller pressure, brakes etc. On a 50 cycle power line, a drop to 49.5 cycles wil

49、l make the recorder run slow by 1% and this should be borne in mind when checking equipment with a specified accuracy of 0.3 percent. 2.2 Routine maintenance 2.2.1 Cleaning From time to time the working parts of the recorder which come in contact with the tape should be thoroughly cleaned. Cleaning

50、of the head faces is particularly important, especially in the case of four track heads where seemingly invisible particles can often have an adverse effect on performance. On no account must any deposits be scraped off with metallic tools. Loose tape dust, may be brushed off. For cleaning of the he