Help Nate fix his Crate...Flexwave 15R

[Goboy77]

New guy sayin' HI.

I picked up this Crate Flexwave 15R for $30.  The input jack was jacked, so I got a new one and got out my T-rusty soldering iron and soldered the new one onto the the PCB.  Yay Me~!  It worked!

I was hoping the bad jack was the culprit behind the loud hum and radio station noise.  It was not.  I have one of those cool magnifier + circular bulb on spring loaded arm lamps and a careful inspection by my untrained eye did not reveal any obvious problems.  Nothing burned, nothing leaking, nothing swollen and no bad solder connections that I could see.

So here are the symptoms.  Radio station pick up is minor, but the hum is pretty loud.  It makes the hum with or without guitar/cable plugged in. The gain/volume knobs do not affect the hum in any way I can hear.  The hum loudness will vary greatly dependant where I stand and how close I am to the unit.  When I position the power cable in a certin way, the hum all but disappears.  In this position I have to strain to even hear it.

I'm attaching a photo, for what its worth, and I posted a schematic for the amp in the schematic section.

Any thoughts are greatly appreciated, and your threshold is very low if you allowed me to become a member :cheesy:

[J M Fahey]

Ok, there's good news and there's bad news (not that bad).

The good one is that the amp is not blown/burnt/nuked  :cheesy:

The bad one is that probably there's some broken ground somewhere, explaining the radio pickup/hum/etc.
Problem is you'll have to find it 

Hope somebody has the schematic and can post it.

The big question is: ..... can you work with a schematic and relate/match the funny drawings to real world parts, plus relating the thin lines to real world connections?

If so, I guess we can help you

Just in case, take and post a couple nice well illuminated and sharp (parts readable) pictures, one from above the PCB showing parts, one be,low showing tracks and solder pads.

[Goboy77]

Thanks for the reply!

I have the schematic and I've posted it in the schematic section of this site.

30+ years ago, I spent a year and a half as a draftsman drawing substation schematics for my local power company, Memphis Light Gas and Water.  I know that in no way qualifies, but I hope it will help me.  I've been looking at the schematic and I dont find it confusing per-se, I "just" (hah, like it's easy) don't recongnise all the parts and their functions.  I recognise resistors, capacitors, test point locations...so maybe not completely hopeless.  I believe I can relate the traces on the PCB to the schematic.  I'll get busy with some better pics!

[J M Fahey]

That qualifies you well enough

I posted the caveat because many do not relate "symbols" to actual copper and flesh stuff, in fact many popular amp kits (Ceriatone) do not even include a schematic, just a layout .... which for us Techs makes it harder to check, believe it or not.

Thanks for the schematic, the pictures I asked will help find real parts and tracks and suggest test points.

[Goboy77]

I was hoping the fact the hum varies depending on where I stand, and the fact that I can all but eliminate said hum by manipulating the power cable into the position shown in the picture, would yield more immediate results.

Having fixed the jack but not eliminating the hum, I gave it up as I lost cause and ordered a Fender Champion 40.  The Fender arrived today ( a rare Sunday delivery, presumably because Saturday was July 4th?) Anyway, it was after ordering the Fender that I discovered I could get rid of the hum by moving the power cord around, and that rekindled hope that maybe I could fix the Crate after all.

Don't need both, either would suit and I can still return either one for a refund.  So, if the clues I've submitted can't point to anything obvious and easy, I'll just return the Crate and apply the funds to the Fender.  It could be fun to mess around with the Crate, but also a distraction.  The Lord knows I've a long list of other stuff that needs to be taken care of.  On the other hand, I do like to save money!

I'll just wait a few days.  If the much in demand "quick and easy" ain't gonna happen, I'll just keep the Fender.

[nosaj]

I would think the broken ground might be right there at the IEC connector on the inside, because of the way you flexed the cable causing it to complete a ground. Another thought is have you tried a different power cable?

nosaj

[Goboy77]

The power cable is "hard-wired"? to the amp.  It's not a computer type that I can unplug.  I've done nothing to it.  That would certinly qualify for quick and easy fix if that's the problem!

[nosaj]

Then in that case I'd check continuity in the power cable. Unplugged of course. Check all 3 wires  one probe on a blade of the plug and the other on the inside. See if moving the cable affects continuity.

nosaj

[Enzo]

I still think it is a grounding issue.  You could have a small burnt open spot on a ground trace to the input jack, for example.  Moving the power cord brings teh substantial field around that cord nearer and farther from the sensitive area.

[Goboy77]

I did find continuity on the ground, but did not check the hot or neutral.  I believe Enzo is right and that will be no quick and easy, for me, fix for the Crate.

I went ahead and popped the top on the Fender box.  It sounds so much better than the Crate, even with the Crate's cord positioned to minimize hum, that fixing the Crate is no longer an issue.  Returning the Crate, selling my Peavey Vypyr 15 on Craigslist, and saving the shipping cost to return the Fender will recapture more than half the cost of the new Fender.  I think it's worth it, and probably the best decision in the long run.

So, thank you JMFahey, nosaj, and Enzo!  I appreciate your help and advice!