bugera 333xl effects loop problem

[gweedo]

Hello, just aquired a bugera 333xl head (out of warranty) with a couple of issues, wondering if anyone could help. First problem : when switching effects loop on or off there is a loud pop thru the speakers , I am assuming this is a noisy relay as it does sound louder than other relays when switching and all cap's, resistors in circuit seem ok, the second issue is that it came with a footswitch that has a 5 pin DIN plug & the amp has a 5 pin mini DIN socket, without schematics its a bit hard to locate correct wires to change plug or socket,could someone help with a wiring diagram, thanks

[Enzo]

I spoke to you elsewhere about this recently.

Does the FX loop pop with nothing plugged into it? Does it pop with a cord plugged direct from send to return?

[gweedo]

Hi Enzo, sorry about the two listings, the loud speaker pop is there if you have a lead plugged from send to return or with no lead at all. thanks for the help with the footswitch I will check that out on the weekend when I have a bit more time

[Enzo]

Relay RL4 is the loop relay. I have no reason to suspect the relay itself, but it is driven by T3 with diode D7 across the coil. An open D7 would make spikes happen, but they would probably burn out T3 pretty fast, so I don;t think that is it.

So find RL4. I have no idea wher any of these parts are located, you'll have to find them. Hopefully they are grouped. FInd D8,D9, hopefully close, and probably next to T4 and R62. Those two diodes, cathode of D9 is +15VDC. Anode of D8 is -15VDC. Unless you are missing a 15v rail , those should be present. And if you ARE missing one of those rails, then there is your problem. the other two ends of the diodes join together and should have zero VDC on the junction. if there is any DC there, there is the pop. R62 connects to that point.

Also somewhere between RL4 and the little reverb board is R55. Does it have any DC voltage on it?

Make these readings both with loop on and loop off.

[gweedo]

Thanks Enzo, I have a pretty busy schedule between now & the weekend. I will check it all out then & let you know how I went.

[gweedo]

Found a spare minute to check voltages, ( couldn't sleep ). I have + 15VDC @ cathode of D9, -15 VDC @ anode of D8 and about 10 millivolts at R62 junction end. R 55 is a bit more interesting, Loop Off: + 12 millivolts @ RL4 end of resistor, Loop On : 8 Volts @ RL4 end, 2.6 volts @ other end. What appears to be pin 8 of RL4 has -9 VDC with Loop Off with 0 volts on the other pins ( not including the coil pins). With Loop On -8 VDC @ pin 8 & -8 VDC @ what appears to be pin 4 . 0 VDC at other pins. Had a quick check with ohm meter, couldn't find components connected to pin 8, (circuit board covered in black film hard to trace circuits). pin 4 is connected to R55.

[Enzo]

I have zero idea what pin nunbers are what in the relay.

So something is coming through the relay onto the signal path.

The FX return comes through the loop level pot, then through IC1b. Check IC1 pin 7 for DC. FRom there we go through 10uf/25v C38, with 100k R77 to ground. That brings us to the relay.

SO in my mind, an open R77 could allow C38 to charge up. A shorted C38 could cause grief. DC coming out the IC could charge up the cap.

You get any DC across R77?

[gweedo]

pin 8 on RL4 connects to R77 & C38, 6.8 VDC across R77
IC1 pin 7 -13.6 VDC
IC1 pin 6 -6.8 VDC
IC1 pin 5 -13.6 VDC
13.6 VDC across R34

[Enzo]

R34? I have no idea where that is.

You have 13v all over that op amp. I'd be changing it.

If you want, remove it, and check the pads before replacing it. I bet the voltages are gone then.

It is a TL072.

[gweedo]

G'Day Enzo, Ive already dropped out pins 5 & 7, voltages are still on those IC pins & not present in the circuit, I've already ordered a few TL 072's (as our local electronics store has just closed down), they should be here early next week.I really appreciate your help, it has made tracking this problem down a lot easier, especially as there are NO schematics available,(to the general public ). I will update you on my progress once its fitted & let you know how I get on with the footswitch. Cheer's

[gweedo]

Finally got around to Replacing IC1, solved the popping noise. In an earlier posting I mentioned R34, That was a typo, should've been R74 which is also linked to IC1.. Now The Footswitch, replaced the pcb mounted mini din socket with a chassis mount din plug, 1 Pin does the logic switching, 1 Pin provide 5 volts for the clean LED, 1 Pin is 5 volts for the crunch & lead LED's, 1 pin supply's 5 volts (when the FX loop is switched on), for the FX LED & 1 Pin is Ground. Pedal is a Bugera FSB 104 pedal with a din plug, all works fine. .. Big Thank You to Enzo for all his help. (seem's to be a bit of a Guru around here)

[Enzo]

The troubleshooting was straight classic approach. It seems like more because I can;t show the schematic.

[maoo35]

Hello, problem connecting footswitch to Bugera 333xxl 212. Footswitch have DIN male connector, Bugera have mini DIN female(looks like PS2 connector without one pin). Anyone can help me, maybe a connector wiring diagram?
Thanks a lot

[gweedo]

Hi, I have a couple of rough drawn diagrams from my note's, if you email me I will give you a copy, hope they help.