AC15CC1 Reverb Repair/Swap Help

[Southpaw]

Hi, I am new to Vox amps and just picked up an AC15CC1 at a very good price. However the reverb and tremolo is not working. Everything else seems to work fine. I did a bit of research and decided to pull the reverb tank to check it first. Reverb tank is a black Ruby Reverberation unit RRVS 3EB1C1B. Upon visual inspection all wires and connections look good and everything looks as it should be. I checked it with my meter on the input and output terminals. Readings were as follows: Input 73.5 ohms, output would flash a value between 150-180 and than just read 1. I switched my meter to the 2k value and tested the output and it read 0.208 ohms. So I am thinking the reverb tank is shot. My question is would a bad reverb tank cause the tremolo not to work or is that a separate issue? Also I do have an old Accutronics 1FB2B1B reverb tank out of an old Traynor, but was hesitant to try it in the Vox as the resistance values for the Accutronics (input 162.1 ohms / output 170.6 ohms) don't really match the Vox all that well. Also according to the model numbers of each the Accutronics has a grounded input and shielded output where as the Vox is totally opposite and has shielded input and grounded output. Any help on this would be greatly appreciated.

[52 Bill]

Welcome to the place.

Readings were as follows: Input 73.5 ohms, output would flash a value between 150-180 and than just read 1. I switched my meter to the 2k value and tested the output and it read 0.208 ohms. So I am thinking the reverb tank is shot.

The readings are fine. On the 2K scale the reading of 0.208 equals 208 ohms. Test the two cables and the connections at the ends for continuity.

Both problems may be electronic. What sort of skill set do you have in working on an amp that is plugged in and turned on?

[Mick Bailey]

The resistance readings look OK to me. You're reading the input directly as ohms, but with your meter set to 2K it's reading 0.208 k Ohms, or rather 208 ohms. This is what I'd expect it to read - I usually think of an output being around 220 ohms. The reason your meter flashes with a reading and then reads '1' is probably this is the over-range indicator and the momentary value is what you're getting as the meter stabilizes the reading.

A bad reverb tray won't affect the tremelo.

Make sure the connections to your tray are good. To test the reverb return is working, unplug the output cable, turn up the reverb and touch the RCA plug 'hot' pin. The amp should buzz just like you touching the end of the guitar lead.

To test the send, connect the RCA input connector to headphones and gradually bring up the amp volume as you're playing. You should hear the guitar through the headphones. as the reverb signal is mono just connect the RCA ground to one side of the headphone plug (RCA GND > sleeve / RCA hot > tip).

[Southpaw]

I'm no tech, but willing to give things a try to the best of my abilities. Hoping this may be an easy fix but either way am quite happy with the amp even if not. Nothing a few pedals can't fix.
I will try some more of the tests that you guys have recommended tomorrow hopefully. I'll post my findings.

[g1]

schematic:

[Southpaw]

Ok, so I tested the continuity of the 2 rca cables that go to the reverb unit and the input cable (red) had continuity but the output (white) had none. I also tested with the reverb plugged in and reverb turned up and got no noise when touching the center (hot) pin of the output cable. I didn't have any earphones to test the sendas recommended, but I would think it's safe to assume that it should work if it has continuity.

[Mick Bailey]

Fix the cable and you're probably going to have a working reverb. Does this amp need the foot switch for the trem to operate?

[Southpaw]

So you think it is just the output cable itself? Not any components that feed into the output cable in the amp itself? The amp does have a jack for a foot switch, but all the controls for the tremolo, speed and reverb are on the amp itself. I thought a foot switch would be optional, not needed in order for the tremolo to work. Is that maybe a Vox thing? No other amp I own requires a foot switch for anything on the amp to work.

[The Dude]

Most all of the Fenders need a foot switch for the vibrato to work. It certainly could be the case here.

[Southpaw]

Interesting. I don't own any Fenders. I do have a Marshall and Randall foot switch tho. I'll have to plug one in and see if it makes a difference.

[Enzo]

Looking at the schematic, the trem oscillator appears to have a FS as a kill. TR1 is held on by a base pullup until it is grounded by the FS. TR1 completes the circuit for the source resistor of MF2, the osc part. SO it ought to work without a FS.

[Mick Bailey]

You said the output cable didn't have continuity, so I'm confused as to why you'd think the fault could be something else. To me, no continuity means if you meter one end of the cable to the other for the hot and ground respectively, one will not give a resistance reading. Did you measure some other way?

[Southpaw]

Input cable, inner pin to outer ring shows continuity. Output cable, inner pin to outer ring showed no continuity. If I measure from pin to pin on each cable or outer ring to outer ring both ways showed continuity.

[Mick Bailey]

I get you. End to end is the correct way - if you measure the RCA plug hot to ground you get the reading of any resistance across the other end. In the case of your output cable you should 'see' resistor R52 (220k) if your meter is on the appropriate range, but you've established the cables are OK anyhow.

Because your reverb and trem rely on low voltage supplies for operation, I'd be inclined to make sure these are good before going any further. An initial check would be to locate the fusible resistor R67 (2R2) and with the amp off measure its value. If this is open then you won't have any low-voltage.

Other than that, how confident are you at taking voltage readings while the amp is operational?

[66 Kicks]

Input cable, inner pin to outer ring shows continuity. Output cable, inner pin to outer ring showed no continuity. If I measure from pin to pin on each cable or outer ring to outer ring both ways showed continuity.

So . . . If these cables are sitting on a table without being connected to anything, there is a very low resistance between the pin and outer ring of the input cable with no fingers touching either? I don't mean a continuity test, but an actual resistance reading.

If the input cable is indeed shorted, this may have caused other problems inside the amp and that cable should be discarded before it can cause any more damage.