Laney V-100R Ch B Drive ckt problems

[nevetslab]

I've got the second Laney VH-100R amp on the bench. It began with two of the four EL34 Power Tubes red-plating (pulling over 140mA) on one side. I removed the four tubes from a second VH-100R that I cobbled together with one of the working tubes from this amp and have reasonable balance now.

I was getting a lot of relay chatter when I powered up, and while I was getting both channels working, this rapid relay chatter would come and go. I tracked down one set of schematics for it from Tube Amp Doctor, I think it was.

Laney-VH100-Schematic.pdf

Working from the Drawing # 2385, following the circuit from input tube V1A, it looks like RLY 1 is shown in Drive Mode. I'm assuming RLY 1 & RLY 2 circuits are shown unenergized. That routes output from V1A to the Drive Pot VR1 to feed grid of V1B. Output from V1B thru C6 is shown grounded at R8 1M. I'm having trouble following the schematic here. The Drive Switch is OPEN for Drive Mode. That would have TS3 turned on, turning off TS2, lighting RED DRIVE LED. It also turns off TS1, turning off RLY1. If the output from V1B was instead at the ungrounded end of R8, then the signal would pass thru to the Gain Pot and feed the rest of the cascaded tubes V2A, V2B, V5B and on to what they call the Master Volume pot. Panel doesn't show anything as Master Volume. Just Volume.

Before I took the effort to remove the Clean CH (A) PCB from the panel, and then gulped and groaned trying to remove the Overdrive/Main PCB from the chassis to get to the bottom side of that board to see if I had solder joint issues with the Relays, and had a bitch of a time trying to get that board lifted enough to see no solder joint issues, I put it back down and reassembled it, restoring numerous LED wires in the process. Digging into these is just NO FUN.

Now I have more problems from that effort. The Drive mode for Ch B (Overdrive Ch) now doesn't work, instead adds hum along with major loss of signal. The Ch A Clean Ch LED no longer lights up, but the channel does pass signal.

Does anyone have a corrected VH-100R Schematic? This one in the set shown above is # 2385 dated 26/4/95, along with that of Clean ch # 2386 dated 14/5/95.

I did de-solder and then re-solder the pins of RLY1 & RLY2 on the main PCB #9079-5 LANEY 2004 & upper Ch A PCB # 9076-8 LANEY 2004. No idea (yet) what has caused the Drive circuit to now stop working, as well as the Ch A GRN LED from no longer turning on. Looks like all of the LED's have a BC237 to short out the LED's when NOT lit. I can light up the CH A GRN LED with my DMM from the wires on the PCB, and the xstrs all measure ok.

[Jon Snell]

"Output from V1B thru C6 is shown grounded at R8 1M. I'm having trouble following the schematic here."
There are a few mistakes in your drawing. I remember C6 is drawn wrong and should be connected to the top (Gain control after the relay contact) of R8.
The relays are drawn in the relaxed position.
Some of these had double sided PCBoards and if the feed through plating is damaged, there will be no signal condition. I can't remember from which serial number it started.

[nevetslab]

These boards ARE indeed double-sided. I had to de-solder the LED wires from both the Clean Ch and Overdrive/Main PCB in order to try and lift that main board out. All of the small in-line PCB wire connectors are gooped with RTV, as are all of the radial electrolytic PS caps, LED's are gooped to the front panel, so getting that bottom board out was a major pain, plus still very restricted to lift out due to tethering of the transformer wires tethered and bundled together under that main board. I'm going to have to lift that up and out again, now that I've got this problem with the Drive circuit no longer working (was until I pulled it up/out for inspection).



The 0.187 Female Quick-disconnects all had a very sloppy fit, and for all I knew, that may have been the source of the relay chatter and not the PCB solder connections on the bottom of the main board. I didn't try that before attempting to remove that bottom board. I had to re-tension every one of those connectors so there wasn't the sloppy fit.



I also found the reverb cable connections to the tank NOT using RCA plugs, but are cut off, with the cable wires stripped and tinned, passing thru the RCA female connectors on the mounted tank, soldered on the inside, as there's not enough space between the tank and the top of the chassis. The first one I had apart, an older version of this VH-100R, used RCA turn-around connectors to join the tank cables with those coming out of the chassis. This one has RCA Female connectors to mate with the male tank connector cables.

[Jon Snell]

That off white stuff is hot melt glue. It doesn't stick to the pcb just the rough bits, wires, components etc.
RTV is gasket goo, for automotive use. Tends to be corrosive as it uses acetic acid as a curing agent.
From your reverb tank description, it sounds like you have had work done to it in the past and not very well by the sound of it.
We did have an issue with the reverb tank going intermittant and that was down to faulty connetions withing the reverb plugs. A replacement phono lead cured that.
Check you have relay supply (+15volts) on the relays before doing anything else, sounds like it may be missing. (If you have leds lighting, the +15volt supply is OK).

[nevetslab]

I found all three Reverb tanks on the two versions of the VH-100R not using RCA Plugs connecting to the tank. Cables instead either have the shield soldered to the GND sleeve of the tank RCA, or carried in thru the pin opening and soldered on the inside of the tank. Space between tank body and chassis not sufficient for even molded right angle RCA plugs. Just haven't ever seen this done before, so assuming this is a factory build?

I have +14VDC on the relays when switched on. I've followed the signal path thru the RLY1(had to hack away at a pile of that glue to get to the lead of R4 finally verifying it did make it to the top of the Drive Pot VR1). , and get continuity thru the Relay in relaxed state (Drive Mode). I'm not getting signal past V1B, so this may be solder joint failure on the lead wires from the PCB to the tube socket. Gotta look at that this morning when I get to the shop. The Gain and Volume pots VR2 and VR3 are working, and turn up the hum, instead of signal. The hum goes up and down with the Drive Pot, so this sounds like an open circuit in that path...just haven't found where yet.

[nevetslab]

I looked at the chassis wiring and that from the Drive pot over to V1 Preamp tube. The shielded wire connection to the 68k 2W grid input resistor had broken away, no doubt from being flexed in the process of getting that Overdrive PCB lifted up and out away from the front panel. Flying tack-solder connection. I re-positioned the wire/resistor re-soldered it into place, and powered back up. THAT WAS IT! Now everything is working again.

Yesterday, I found trying to remove the tube shields from the preamp tubes was nearly impossible. None want to rotate to align with the detents of the socket mating flange to allow lifting them up. I'll check that again when I flip the chassis back over prior to sliding the chassis back into the cabinet. I've had some shields be stubborn, but this was ridiculous.