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In flagrant violation of my self-imposed rule not to buy watches with lug widths larger than 20mm, I find myself in possession of a Seiko 7548-7000 dating from June 1982 (22mm in case you were wondering). My excuse is that the bid I submitted was not entirely serious but ended up winning the auction, probably because other potentially interested parties were put off by the watch having been described as unresponsive to the fitment of a fresh battery. I confess too to a certain fondness for the model, largely because my first semi-serious attempt at a watch refurb was the fettling of a pepsi variant of the same (see here). It is also a watch to be respected because its design was born from the tail end of a golden period of creativity for Seiko and, as a result, it is a watch whose quality shines through, unencumbered by the air of penny pinching evident in the second generation 6309 automatic diver’s watch introduced three or four years later and with whom it shared its case design.

The auction photos suggested that this particular watch was in tip top nick, non-functioning movement notwithstanding, and with it in hand, that impression is not undermined.

Seiko 7548-7000For sure, it is a little dirty but it looks to have been very well cared for over its 33 year life time, with the dial and hands in particular looking super, the bezel original and only sporting a few minor scratches and the crown and case tube still in possession of the full quota of thread. With a movement as potentially accurate as this robust old quartz, it is perhaps not surprising that previous owners might not have had cause to undo the crown very often.

It doesn’t look either that this watch had seen much watchmaker action: the case back shows two dimples on its timeline indicating battery changes in 1985 and 1991

Seiko 7548 case backalthough, any since 1994 would not have appeared on the case back, I suppose. Still, the movement looks clean with only some tarnishing to the model number plate on the green circuit block betraying the watch’s age.

Seiko 7548 movementThe battery is missing from this shot but when I received it, one was fitted and the watch not running, as advertised; a substitute yielded nothing in the way of meaningful action either. Its non-functioning state was enough to prompt me to pick up a very cheap but working 7546 quartz watch from Ebay to farm for parts as required (I was thinking at the time that the coil was probably shot).

Slipping the movement out of the case and the dial looks every bit as good as hinted at from the exterior view, barring a slight mark to the left of the 5 marker.

Seiko 7548 dialDial off and we see a calendar-side layout all but identical to the 6309 on which this movement is based

7548 calendarwith pretty much everything looking essentially mint. The resistance offered up by the hands when I removed them suggested that this is the first time anyone has gained access to the movement innards since 1982. I’ll skip the breakdown of this side of the movement as we’ve been here before with the 6309 (see here, for example) and concentrate instead on the relative unfamiliarity of the train and circuit side.

Seiko 7548The layout is pretty conventional with the train wheels and bridge sat in the centre, the coil at the bottom and the quartz oscillator and circuit hidden on the reverse side to the left. The gold coloured screw to the right of the movement nameplate is a trimmer condenser, used to regulate the timing of the movement.

The green circuit block is secured by four screws, two of which also secure the battery-holding spring. With it removed and turned over we can see the quartz oscillator and reset pin, the latter coming into play when the crown is pulled out to the time-setting position.

Seiko 7548 circuitThe removal of the circuit block allows access to the coil and train wheel bridge.

Seiko 7548 coilA slight hiccough follows because, having removed the crown with it in the time-setting position, the second setting lever (effectively the equivalent of a hacking lever) is sitting snugly against the fourth wheel, making extraction of any of the train wheels ill-advised.

Seiko 7548 setting leverRefitting the crown and stem and resetting to the normal position frees up the fourth wheel

Setting lever second clickpermitting the removal of the train wheels and providing access to the centre wheel bridge.

7548 centre wheel bridgeThe tarnishing of the model number plate on the circuit block was something I wanted to sort during the cleaning process. Obviously, attempting to clean it in situ is inadvisable but it is easy enough to remove by pushing the securing tabs from the rear.

7548 tarnished name plateFollowing cleaning of all of the non-electrical movement parts in the watch cleaning machine, reassembly proceeds as follows: First up, fit and lubricate, as required, the clutch and stem followed by the setting lever, yoke and setting lever spring.

Seiko 7548 main plateTurn the movement over and fit the centre wheel and positive battery terminal connector

Seiko 7548 centre wheelfollowed by the centre wheel bridge, rotor stator and reset lever.

7548 reset leverThe train wheels, step rotor, second setting lever and reset lever come next, with the crown set to its normal position to aid fitment of the second setting lever.

Seiko 7548 train wheelsSetting the crown to its second position frees the lower part of the reset lever to move downwards against the sprung load exerted by its upper part, with the end of the stem no long sitting against the pin to the rear of the reset lever. This downwards movement simultaneously allows the second setting lever to rotate clockwise and make contact with the teeth of the fourth wheel and the end of the reset lever to move downwards and make contact with the reset pin on the rear of the circuit block.

7548 second setting leverThe contact of the reset lever with the reset pin stops the output signal from the circuit block but maintains current to the quartz oscillator so that it is ready to start again when the crown is pushed back to the normal position.

The remaining steps in the reassembly of the movement are straightforward but in taking them, we need to test the function of the original coil and circuit. So, first refit the original coil and anti-magnetic shield followed by the circuit block, now reunited with the cleaned model number plate.

7548 circuit block backI secured the circuit block with a pair of screws borrowed from that spare 7546 movement because I did not want to refit the battery securing spring just yet. Pressing a fresh battery into the battery holder and I was relieved to see the movement spring into life. It looks as though it was just dirt and dried out lubrication that was preventing it from operating rather than any faults with any of the electrical components and so for the moment, that 7546 can breath easy.

Moving back to the calendar side, reassembly appeared to have gone smoothly but when testing the operation of the setting and quickset, I noticed that during the time setting operation, the rotation of the setting wheel was dragging the day/date correcting gear across to the intermediate day correction wheel, mounted on the minute wheel bridge, causing the latter to rotate. With the day wheel fitted this would result in the day wheel rotating inappropriately during the time-setting operation.

7548 minute wheel bridgeThe reason it was doing this was that the setting wheel lever was not sitting low enough against the movement with the result that the underside framework was not staying hooked over the pin on the main plate (illustrated below in a photo of a spare 6309), thereby allowing the whole shebang to drag to the left.

7548 setting wheel lever pinI removed both the setting wheel lever and minute wheel bridge and gently bent both downwards slightly, with the result that the latter exerted a stronger force on the former when tightened down and the setting wheel lever then sat slightly lower. A retest and all seems well.

Attention now turns to the case. The usual breakdown into constituent parts

Seiko 7548 case disassemblyis followed by a thorough clean. Out with the old gaskets and crystal

7548 gasketsand in with the new, together with a fresh battery.

New gasketsThe crystal, incidentally, is a tempered mineral facsimile of the original, complete with frosted chamfer and sourced from Ebay seller kleinvintagewatchparts. You can see that lovely frosted chamfer in this shot of the crystal refitted to the case and awaiting the crystal retaining ring.

seiko 7548 caseWith the dial and hands refitted to the movement and the battery retaining spring back in position, it is time to fit the movement to the case,

Seiko 7548 movement serviceclose up the case back and turn over

Seiko 7548 case without bezelbefore refitting the bezel.

Seiko 7548 restoredThe watch would originally have been fitted with a GL831 straight-vented rubber strap rather than the Z22 curved-vent strap it came on

1982 Seiko Catalogand so with a modern equivalent secured (4FZ0AZ), we are all set to wrap this one up.

Seiko 7548-8000 from 1982All that remains is to check the timekeeping and regulate as required. In this case, the watch was running a little fast for the first day or so but an eighth turn clockwise to the trimmer condenser and the watch has lost just under a second in the past 5 days, well within the specified accuracy of 15 seconds gain or loss per month. Let’s conclude with a wrist shot on the new strap.

Seiko 7548 on the wrist

 

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