Rivera Bonehead amp powers up but nil output !

Hello guitar amplifier enthusiasts ! This week’s blog could easily be given an alternative title the lights are on but nobody’s home, as those were the classic symptoms we were confronted with when powering up the Bonehead for the first time. This is a relatively complex repair example to describe and photograph for a blog, which is why it’s taken us over two weeks to get it together.

The Paul Rivera Bonehead amp is a huge, rather heavy, 100 watt 4xEL34 valve (tube) head with three discrete pre-amp channels, and incorporating the Los Lobottom woofer output to drive a separate low-frequency amp/speaker system. The Bonehead can be (and normally would be in this case) operated without the Los Lobottom feature connected to anything. The design concept is attributed to guitarist Steve Lukather, formerly of the U.S. band Toto.

This Bonehead was shipped up to us some time back by Bondi Intermusic (Sydney), on behalf of one of their customers. At first appraisal, we had no idea what was going on – the amp powered up OK, and all the circuit conditions looked normal, power supply voltage readings were in the ball-park of what you’d expect in such an amp, both high-voltage and low-voltage supplies, and yet there was zero output from any of the three channels, and none of the front-panel status LED’s were active.

Discussion of the amp’s history with the customer, Paul, revealed that this same fault had occured a number of times in the past, with the fault condition returning almost immediately after the customer received the amp back from repairs (previous repair attempts undertaken by a Sydney based tech not personally known to me). This is a pretty rare amp in Australia and the first time we have ever seen an example of this model, so the first thing was to try to track down some official service info/schematics from Rivera USA, via their Australian distributor. This took quite a while and finally we received a faxed copy of the schematic, which was a little lacking in resolution compared to a soft copy, however much better than nothing at all !

All the switching in the Bonehead, including for LED status indication, originates in a complex circuit of seven CMOS logic IC’s, mounted in 14-pin and 16-pin IC sockets. There is other discrete circuitry as well, to drive the LED’s and the opto-couplers. It would be very difficult to service this amp without a schematic diagram. Thankfully, Rivera chose to install the IC’s in sockets. BUT, the quality of the sockets they used was NOT professional user standard. I remember from my earlier career in the Telecommunications industry, when Telecom circuits went from electro-mechanical to 1st generation digital/solid-state, we had endless faults caused by the fact that IC’s weren’t seated properly in cheapo sockets.

It was now obvious that the fault causing nil output was not in the valve (tube) cicuitry at all, but was the result of a non-functioning switching circuit. Due in part to my history of bad experiences with cheapo IC sockets, and also due in part to the complete lack of voltage and logic test points on the schematic diagram, it also was now obvious that I should replace all seven IC’s and most importantly, the IC sockets, using only industrial quality machined pins sockets. Interestingly, the previous service “tech” had chosen to carry out a quick fix, basically just trying to hold the IC’s in their sockets with some kind of goop, rather than actually cure the problem once and for all.

The main board now had to be stripped out of the amp chassis, which involved removing all control knobs and pot nuts, etc, as all pots are p.c.b. mounted in Rivera amps. The IC’s were removed then the old IC sockets were removed from the board – this required desoldering  the socket pins on a double-sided, plated through hole board. Rather laborious and tedious and a task requiring a great deal of care so as not to damage any of the pads and through plating, otherwise we would be up shit-creek, basically. Having cleaned up all excess solder the next task was to install these new, industrial quality 14-pin  and 16-pin sockets. Once again, applying enough heat to make sure the solder ran through to both sides of the board, but not so much heat that we damage the board.

You can see in the previous three photos the underside of the board with the soldering of the IC sockets in the foreground, and two views of the component side of the board with the new sockets installed successfully. The next two photos show views of the board with IC’s installed in the new sockets, with the complete switching circuitry in the foreground.

But now we hit a snag ! Look at the photo on the left. The IC’s designated IC306 and IC307 are positioned too close together on the board, which means that the two IC’s cannot be inserted fully into their respective sockets. HUH ?? No wonder the previous tech resorted to using goop to hold the whole thing together – trouble is, it only worked for about 5 minutes that way. I had to use secret Aussie male ex-Telecom Australia technical workforce service techniques to get both IC’s into their sockets. But seriously folks, this kind of design boo-boo should not be happening in this level of equipment.

The repair job was finished with some routine tasks, including rebias of the EL34 output valves, and cleaning of jacks with DeOxit and pots with FaderLube. Power output test and electrical safety test were both fine. The Bonehead is probably the least successful amp from the Paul Rivera range, judging by Rivera user forums. How did it shape up in the final play test ? The three channels, clean, crunch and full-on distortion for want of a better description worked well, allowing fine control adjustments as each channel has its own independent level and EQ, as well as “Ninja” boost and other features. The robust FS8 footswitching unit works well – the use of CMOS logic IC’s to control the switching enables Rivera to use simple momentary footswitches to activate channels and FX Loop. The only criticism we have here is the continued use of DIN plugs and sockets, which on the road are a constant source of problems – they are just too flimsy, resulting in intermittent connections. This criticism applies to many commercial manufacturers, not just Rivera.

Rivera amps usually have a “Fender” voiced channel and a “Marshall” voiced channel. I usually much prefer the “Fender” voicing on these amps, and that applies to the Bonehead model as well. The “Marshall” channels are just not that convincing to my ears, but it’s very much a personal thing. Paul Rivera is well known as having redesigned some of the Fender amps in the early 1980’s and turned that company’s fortunes around in the amp business. The Super Champ is my favourite model from that era. Bondi Intermusic’s customer was most pleased to have his amp back again after so long, working properly at last !!

In coming weeks we will have another major 1970’s Musicman refurbishment, this time a 4×10 combo (rare around these parts), an overhaul of a very rare early 1970’s Marshall 1×12 tremolo combo, a transformer replacement in a mid-1960’s made in Sydney Galaxie, by Vadis, ie Soundcraft Industries, went out of business back in the early 1970’s. We also have more amps and cabs from the Richards Amplifier Company nearing completion. Don’t hesitate to email me re any of this stuff – regards, Ivan.

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