Voltage between the two black wires coming into the board is 6.3 volts.
Voltage to the two wires going to the clock is 0.85
Now 0.85 VDC serving as 1.5 will not go, particularly when its derived supply source . . . .6.3 VDC drops on down, say, to it then being 4.5 VDC, from the running DC gear train motor loading down on that supply line.
Now in my looking at all of those " purty " carboniferous film reeeee-sistors , and all, being of moderate to low resistance , I hesitate to cast any doubt on any of them.
It goes, as well, for any of the discrete, inherently uber reliable silicon planar family transistors.
Nor, any suspicion, for the, far board end mounted, 1N4007 "steering" diode which serves to isolate the battery cell set, IF you have then additionally installed , a plugged in power wall wart, at the sacrifice of a mere 0.700 millivolts voltage drop.
Instead, I want to zero in on the specific E-cap for that 1.5 V supply, which is serving as its power reservoir.
Its the circuit board outer board edge mounted unit, instead of its twin, which is being more center board mounted.
Now the question is being . . .if . . . .you are "into" electronics enough, so as to have another 100 or 220 or 330 or 470 or 1000 ufd at 10-25-35-50 working volts . . . . . E-cap.
OR . . . . . you might have some old electronics that might provide such values of a "loaner" for our test.
Where we then shunt that suspect / ? cap . . . .with all important . . . PROPER / SAME . . . . polarity of leads mating up.
With a pulled E- cap PWOBABWY having vewy-vewy
*** short leads, you should solder tack on some short wire extensions using bits of scavenged, small gauge insulated solid copper wire, say, from some CAT 5 cable.
You install and then see if the 0.85, then rises on up up into the ~1.5 V VDC range.
WORKAROUND . . . . . if possibly not having the above part or its / a substitute sourcing
That would be the inter swapping of the twin, like rated E-cap units.
BUT with the prior initial garnishing of some intelligent info from the units.
That would be done by using your meters additional AC voltage reading capability.
Considering that we are SOLELY using the wall wart for power . . .no batts . . . . and in the same manner ( its voltage settings) that has been used all of the prior years.
Now, set up, and in the same manner that you read out the 0.85 volts of the unit .
Then you additionally switch to AC mode and see if there is being a readable AC reading . . .which would be the degree of ripple inherent in that wall warts design. As loading upon the supply is increased the ripple increases.
Anyhow, switch downrange on the meter until there is reference able, within scale reading . . .( Unless your unit is being AUTO-RANGING)
Got that ?
Then lets mark our suspect cap so that any loose off board cross shuffling of the pulled units, results in the reinstalling them in their same identical places !
When reinstalled and the voltage is then up towards that 1.5 level we had a weak cap.
If being about the same, then remeasure that ripple and see what it is now with the cap interchanging.
If reading lower ripple, then the swapped cap has more capacitance than the prior original unit, or more ripple signifies less capacitance.
SO O O O O O O . . . . .if having used the final procedure, with out any good results.
Now, unplug the wall wart and revert to installation of the C cells for battery power .
And since you NEVER told me if only 2 leads are coming in from the battery holder instead of the other referenced units use of 3 leads I have to deduce, only the two end small gauge black leads connect into the PCB from the battery pack / holder..
THEREFORE . . . . the reliance of the drop of that 4.5 VDC from the serial cells to the lower 1.5 needed by the clock . . . . . to ALSO be accomplished by on board discrete components.
So now measure the 0.85 VDC connection to see what it is, when using battery power.
With use of battery power, we could also give your wall wart and its internal E-cap filter and its subjecture to distressing adjunct transformer heat, towards its overall inherent capacitive health.
Talk to me . . . .
A FINAL . . . . . " Waaaaaaaaaaaaay Faaaaaaaar out thar' . . . . . in left field possibility.
If . . . you are testing with the pcb mounted with its 2 screws installed.
I find no fault with the screw closest to the motor being installed.
Now . . . .
CRITICAL CITY . . . . . is being the second screw and if those 2 screws composition are being black oxide coated metal screws.
If they are being black "plastic" / Delrin / or / nylon screws . . .
NO problem there.
If being metal screws and with any burr (s) . . . . . . look at the circuit foil underneath, that is being almost totally covered by the screw head at its center board side.
Then look at the other screw heads half, that would be towards the rear edge of the board with there being another separate foil trace that runs across that edge.
Considering the " slop" / lateral play in an oversize hole and the mounting screws effective shank diameter, does it look possible for a far edge positioning of the board, with a "HEALTHY" tightening down of the screwdriver, . . . . . . to then have a screw burr pierce conformal coating on foils to create a shorting between those two separate foils ?
If you have always tested with the board loose . . . . . . there is no possibility . . . . . but I would make an insulated washer to install under THAT screw head.
FIO . . . . . . . .E-caps and their sometimes SHORT Longevity
Most of our modern time E-cap failures will relate to ones being used in switch mode power supplies and their getting absolutely
HAMMERED with strong square wave forms, repetitively
HITTING them 10's of thousands or . . . on the highest end . . . millions of times a second.
Gradual deterioration and inherent electrolyte depletion and associated / related inherent temperature rise can then speed up deterioration to that threshold where the unit is running excessively hot.
So hot, that eventually, that very last bit of internal moist electrolyte is vaporized into gas and if enough pressure is present, it will cause rupture of the mechanically weaker imbedded X crossses that are stamp pressed into the end of the aluminum case top.
THEN . . . . .you will eventually be left with the tapering effective capacitance of a now truly
DRY electrolytic.
I have had . . . the un taxing applications . . . . . of like E-caps, being used in 2 transistor radios of 1956 and 1961 vintages that are still playing for me after 65'ish years .
Plus a Boom box, 4 and 8 track players , reel to reel tape recorder, calculators, car radios from the 60's-70's , at their 50ish years of age.
Post addenda . . . .
I read back and run across :
I tested the black and red leads that run to the clock (with the batteries installed) and it shows zero voltage.
(I wasn't expecting that low of a level ).
Thaaaaaaaaaaaaaaaaaaaaaaaaaaassit . . . . .
73's de Edd . . . . .
*** Copywight 2022 by Elmer Pee Fudd. All wights wesewved.