Rockola type 48350 amp question

I have a Rockola 470 I've been repairing since a neanderthal had his way with the gripper assembly, but I must not digress. It has an amplifier issue I need some guidance with. The sound is clear but I am unable to get significant volume, it is moderate at best with all tone controls at max as well as the external volume control at max.
I have a spare amp and it works normally in the juke. I have swapped the power supply boards which made not difference in performance.
I replaced all the caps in the capacitor board, also no improvement.
When I swapped the Driver boards the amp that was putting out minimal volume was now putting out significant volume and the spare amp is putting out min. volume.
My question is....what in a single driver board would affect total volume....or is there a component in both boards that could fail simultaneously???
I have checked all but the Q4LR transistors with a super cricket transistor checker, which can test transistors in circuit for gain (go-no go test). The two Q4LR transistors were soldered in too close to the board to get the wire clips to grab on to the pins. Visual inspection of the caps do not indicate an obvious problem and I have not replaced the caps in either board.
I checked the bias voltage and noted the voltage at test point A was approx 1/2 the voltage at test point B, which is what its supposed to be. Though when I was testing the right channel the test probe must have misbehaved since the was a small spark and a resultant blow fuse. I figure the probe may have touched an adjoining connector, but though I would include the info in case it is indicative of something other than a slip of the hand.
Any suggestions would be appreciated. Thanks, Craig.

Visually inspecting capacitors is not a reliable way of "checking" them.
The same goes for resistors.

Probably some bum electrolytic capacitors in there.

Thanks Ken and Matt, was just trying to figure out what on one board might affect both, but I guess its probably a bunch of bad caps on both boards. Is there an easier way to test these components besides de-soldering one side of them. The electrolytics on the board I will just replace because of their age and the board is the problem. Is there a quick way to check the resistors in circuit to get a rough idea if they are bad?
Thank you again , Craig.

cmangeng wrote:Thanks Ken and Matt, was just trying to figure out what on one board might affect both, but I guess its probably a bunch of bad caps on both boards. Is there an easier way to test these components besides de-soldering one side of them. The electrolytics on the board I will just replace because of their age and the board is the problem. Is there a quick way to check the resistors in circuit to get a rough idea if they are bad?
Thank you again , Craig.

Nothing's "quick" or "easy" about proper serving.
The color coding, along with the schematic, should be all a tech requires.
To "rush" or "skip" things only amounts to frustration and errors, and my customers wouldn't appreciate that.

Hi
Did you check the preamp boards and tone control board. Also a bad filter cap(the large one on the front can cause intermittent volume problems) in addition to a dirty volume control pot
regards
Clones

Clones, I did not pull the preamp boards since the problem corrected when I swapped the driver boards. I used a fader lube/cleaner in the volume control pot though it was not exhibiting problems prior to it. I like shoot all the pots and switches that I cant get to the internals on with the stuff. Its a deoxit product.
MattTech, I am new to the jukebox scene and its been 30 years since I was in basic electronics in high school and my learning curve it a bit off with age. I was looking for a quick trouble shooting way to see if a resistor is potentially out of spec before desoldering every resistor. This is a hobby for me not a business, though I would like to maintain quality in my work and appreciate your input and help.
Thank you both, Craig.

Craig,
As far as I know, there is no sure-way to check resistors "in circuit", as there MAY be something else in that circuit that will change the reading. I usually check them in circuit, and if not too far off, accept them as OK. If the reading is "too far off", and I don't know the circuit, I will de-solder at least one side of the resistor, and check it, prior to considering it OK. Ron Rich

Thanks Ron, that was what I was looking for. I had heard something about a general thumb rule, but was not sure what it was. I have been accepting the resistors as is since the amplifiers usually work after replace the electrolytics. In the pre 70's jukes I replace all caps except the ceramic and mica, in the mid to late 70's jukes of mine I have been replacing the capacitor board caps and the power board caps, but not the other board caps unless there is a visible or audible problem noted.
With this current amp issue, I had narrowed the problem to the driver boards. Based on the advice received earlier, I will recap those too and thought I would check the resistors if it did not involve desoldering them all. If the recap does not solve the problem I will look at replacing the resistors and desoldering and testing the two transistors I could not test in circuit.
Thank you again, your help is always appreciated. Craig.

PS: Do you or anybody else know of somebody in the Seattle, Tacoma, Olympia or KItsap county area that would consider having an apprentice to help refurbish jukeboxes. I could provide one day a week free labor in exchange for knowledge. I don't need a job, I want to learn more about jukebox repair.

Craig,
IF you have two identicle boards, test the resistors "side by side"--they should read "reasonable close" on both boards--unless one or ---oops--both are bad ? Ron Rich

Ron, checked both board's resistors side by side with similar readings and close to what the color codes indicated. I pulled the caps and found 3 bad ones, two in one board and one in the other. The 22uf/70v cap was bad in both boards. The new ones I had are a little overkill, since I only had 450v caps in that value. After replacing the caps the amp volume was great.
I have a 60 hz hum that is noted from the speakers. I pulled an amp out of a working 464 and I got the same hum from the speakers. When I installed the rebuilt amps into the 464 there was no hum. I am ruling out the amps as the source of the hum. Sounds like the hum in a fluorescent light fixture. I pulled the bulb in the lower cabinet but it did not clear the hum. I don't have a key to the upper cabinet back to check that fixture, the lock is different then the lower cabinet. I will check through my keys to see if I might have a match, otherwise, it will get drilled and a thumb lock will get installed in its place.
As always, if she is a hummin, I try to teach her to sing, but a constant 60 hz just doesnt cut it. I figured I would beat some of you to the punch line.
I don't notice the hum when music is playing (probably blends in), but it is noticeable right after the mute circuit cuts out and up until the music starts playing.
Could the power supply induce this hum? If so what would be the possible cause and corrective action.
Thanks, Craig.

Craig,
I don't know RockOla amp/model numbers, but I have run into "hum problems" in solid state Rocks before. It was caused by the "point to point" green/yellow common wires used. Make sure all brass nuts are tight, ARE brass, and all eyelets are clean, also-- Ron Rich

Thanks Ron, I will check and clean them all and see if it takes care of the hum. Will post results.
Thanks again, Craig.

Sorry it took so long..... I checked all the grounds for corrosion, tightness and verified continuity through the ground loop everything checked out good, but still had a hum. Did some additional research on line and there is a large cap that is supposed to remove transformer hum. I recapped the amp but not the power supply...so I recapped power supply and the hum has been banished from the juke.
Thank you all for your help and advice.
I just picked up 9 more jukes from an auction of a vendors storage warehouse (50 years in the business). A couple Seeburg C's, a J, 5-wurlitzer 2610's and one 1500. Was a bit of a drive but the prices were extremely reasonable, filled the truck and trailer. Also picked up 4-3w1 wallboxes, a couple seeburg 1/2 round speakers and a couple directional speakers. Lots of projects to come and I could not buy the parts for what I paid for the complete juke.
Craig