Cut out in use then came back. Next time failed to give output but owner noticed clip light in pre-amp functioned as normal Now I have it, I cannot induce it to fail. Anyone know of generic/specific Eden problems? Likely suspects the discrete wire IDC connectors for power and signal interconnects, unsupported wire-wounds on end, mains thermal switch. Anyone know the identity of the valve/tube ?
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Thanks for the info. Do they remove the valve labelling ? no trace of anything on this one. Send/return switches are the first things I look at with this sort of problem along with speaker plug/lead . I wondered if there was any Eden specific problem areas. I've not checked it out but is that a thermal cutout in the mains feed , rather than filter, to monitor general chassis temperature, not the output N/O(cold) one for the fan
Their power supply boards have been known to become intermittent even though they are double-sided PCBs. You may really have to pound on the filter caps to get the bad one or the bad connection to act up. Also look underneath the supply PCB for high watt ceramic resistors sitting on the chassis with heat sink compound on the chassis while they are soldered to the board but a lead may be broken and only touching where it's supposed to be soldered.
Sometimes the zeners and their current dropping resistors (more ceramic ones) for the plus/minus low voltage supply become overheated and melt solder or get bounced out of whack resulting in a loose lead.
I would suggest to run a signal thru it directly into the scope bypassing the dummy load while tapping and wiggling things around or get it heated up with a load and tap around. Try it both ways, but do it the cool way first, right? Checked the pots for loose cases? Customer already ruled out his bass, instrument cable, speaker cable and cab or did you? Retighten the tube socket terminals and clean them? Detachable AC cord plugged in firmly by the customer? Have him/her demonstrate without saying anything first. Then again, you just may have to have the customer come in with their entire rig and demonstrate the problem. Whatever it is, good luck. I know the feeling.
re solder all connections on pc board but we have seen the speakers in these amps fail frequently. check the pigtail leads on the speaker basket, damaged leads from loud playing can cause what you describe, intermittent output. play the amp really loud to trigger the symptom, with a bass. or tap on the pc board with a plastic handle to find evidence of the bad solder connections. eden sells the replacement basket which bolts to the magnet. easy field replacements. the valve is ECC83.
I did not like the front panel switch in line with the speaker line. In standby instead of cutting/shorting the main amp input you switch out the speaker. IDC interconnects on the speaker lines and power lines seem a bit irregular to me but as cut out rather than distortion those power lines presumably ok. As 2 main bass speakers plus 1 in the cab, as sound died unlikely a problem with a speaker but will check the wiring in there as well as the other likely suspects.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I haven't come across one of these, but I can't help thinking that a front panel switch in line with the speakers, hooked via *any* kind of 'pin' connector, let alone IDC ones, has got to be one of the most ludicrously crazy pieces of design work I have ever heard of - especially in a bass combo with two drivers in it. Peak currents of many amps will be (attempting ! ) to flow through this combination ...
My thoughts exactly, someone fumbles around the front panel with full load going through amp and breaks the line to the speaker at this switch.
Anyone know what the function of the 12V, 10 W "festoon " bulb in the variable crossover in the cab is, fuse? variable impedance element?. Working order but just curious
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
That's probably your culprit... going below the minimum impedance. What is it rated for, what are you running it at? SS amps overheat when run below their rated min imp. __ Steve .
I think I'll bypass this front speaker switch and wiring. Its only rated 3amp and thats for AC, could easily be the problem, let alone potentially "fatal" to the amp. The cab wiring and pair of 4 ohm speakers in series seem fine. I may trace the circuit around and between preamp o/p and amp i/p and change that switch to a line level cut function.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Eden used to have such a good name, yet here are all these posts about goofy design issues and recurring problems, I wonder if this dates from them being borged by the dreaded big fat corporation?
How could the switch be "fatal to the amp"? Designed appropriately, it's there to disable the speakers in the event that one elects to operate things 'silently' as in use of stereo phones or in certain recording situations. It isn't a common failure mode. Yes, an intermittent switch will shut down the speakers but as far as the power amp finals are concerned, "fatal" is impossible as no current would flow when imposing an open at the load connections. Here's a tip: Instead of poking around blindly, give Eden a call. They'll not only send *any* schematic you desire, they'll also be the most helpful resource out there... since they spawned the thing.
The output employs thermal protection via use of an agc circuit which also operates the cooling fan. Have you cranked the thing up against some dummys in order to test for thermal related shut down? You should.
Any chance that the owner/operator is using too low of a load impedance? IIRC, the agc circuit can shut the power amp completely off. Barring any "connection-based" problem (previously mentioned), a guess would be that something in the agc circuit is failing or theres a problem with the impedance at the load.
Here's a simple experiment unless you have a heart problem. Find a small 12V relay , connect to a 12V dc source, hold the relay contacts between thumb and index finger and disconnect the wire to the 12V supply. This simply demonstrates the power of back emf and V=L* dI/dT, speaker inductance about 1mH and peak current through a speaker of maybe 20 to 50 amps. If those few hundred volts (at least) speaker induced back emf exceed the breakdown voltage of whatever partial contact gap, not the final gap, soon (microseconds) after the switch break/ poor IDC contact/poor pcb header pin contact then goodbye pa.
It would not take much fumbling in poor light, drunkeness, confussion or whatever to flip that switch in full use , its not recessed and in the back of the cab. The owner does not use the switch so I will block off the relevant outlet with a nylon bolt pushed in the 1/4 inch socket as a reminder to him, not to use. The other 2 paralleled outlets are not switched, but I may hardwire/solder back to the pa.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Found another nasty under the ps board but don't think it is the main problem. This pair of wires to the speaker switch had one of the wires squashed between a large W/W ceramic cased dropper under the ps and the chassis. Melted through but as it cuts the earth to the speaker presumably no problem as such and wire not broken. But there is smoke blackening or something grimy in that area but it could be a small electrolytic parallel to the fan cooked as it is directly over the large droppers and leaked electrolyte but all rather nasty. The aluminium of the chassis directly under this particular dropper has a strange flecked grey corrosion or something that probably more likely due to electrolyte rather than vapours off the charred PVC insulation. I don't see why this insulation has charred rather than just melted as the owner never switched this speaker switch, I assume somewhere maybe ages ago it was open at some point
Anyone know the function of the big triac on the mains, crowbar operation to blow the mains fuse if too much mains power drawn ?, I've not traced any triac associated line back into the amp that could trigger it as more active amp protection.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
The thermal protection circuit is activating before the 60 degree centigrade fan switch is cutting in, under high load. The fan switch temperature , testing in isolation , is about right. I'd rather change the switch to a 40 degree one rather than tracing the drift in the thermal protection circuit. Any advice? or even if there is a recognised cure in the thermal matching circuit ,eg replacing/matching Vbe of the sense transistors.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I've never had an LED causing failure of an amp. Intermittently o/c losing the fan supply ok signal that goes through this LED to the pa causing it to shut down . Also not passing current to the power-up hold-off circuit so pa failing to come on, thinking the fan supply was absent. Like the fan lytic, both perched right on top of two large droppers on the ps board.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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