Help with Mesa Boogie Maverick Dual Rectifier head

[clinkous]

I acquired a Boogie Maverick head with no pilot light on power up and a burned connector to the main board.


Both burned wires are solid green and I have not traced them yet. Where can I get this type of connector? I searched around but don't know exactly what to call it. I know it's not the problem and am sure I'll be asking questions when I've delved further, but I would like to know where to get these connectors if anyone could help.


Thanks in advance
Chris

[lowell]

Might have to contact mesa boogie for that harness. Pretty sure the connectors come loaded with wires.

Also look at the pcb trace for all pin5 of the power tubes. It looks like it's been overheated/stressed. I'd check continuity there from the bias supply AND if it were me I'd run some buss wire all along there just to be sure. Don't wanna risk the negative bias being intermittent.

[g1]

They are called molex.
You can always bypass it and solder the wires directly to the board, but it will make future board removal more difficult.

[clinkous]

Thanks Lowell. It just looked like the wires were pushed into a connector that cut into them. My old peavey stuff is like that. I will check what you suggest when I pull it apart tomorrow.

Chris

[g1]

It just looked like the wires were pushed into a connector that cut into them.

That is how they are done.
Search for molex connectors.

[lowell]

I said "pretty sure"

Still wonder. Do these amp companies get these as harnesses, or connectors and wires? I'd imagine they dont waste their time assembling that. Just a thought.

[Enzo]

Assembling them is exactly what they do. It takes just a few seconds to stick wire ends into the crimp machine as they are stamped down into the IDC. In fact we have a local manufacturer of industrial equipment that advertises for cable assemblers regularly.

Molex makes a million connectors. These are part of the KK-156 series. The pin housings - the plastic part - are inline. The wires on some of the connector bodies wil get crimped on pins which are then snapped into the housing. Yours however are what we call "insulation displacement connectors", or IDC, and as was surmised, the insulated wire end is pressed into the slot on the pin, which cuts through the insulation to make contact with the conductor within.

If you plan to replace the connector, using an IDC type will be a real pain. They make a special tool for punching down the wires. What I do is replace it with a crimp on style. I clip off the old connector, strip and crimp new connector pins on the wire ends, then snap them into a new inline housing.

However, I would wager those two wires are the heater wires from the transformer. is that the case? Those high current connections are more than the connector can handle. SO one solution is to cut out the burnt part, leaving two partial connectors. We will push those remains back down in position, leaving the two burnt pins bare in the middle. We do need to clean the char off them, and check underneath to make sure the solder is intact. Then we strip a clean surface on the wires and solder them directly to the male pins.

Sure, it is a bit more difficult to remove the board, you'd have to unsolder two wires. But how often does that board have to come out?

[clinkous]

Thanks Enzo,

They are the heaters. I'm going to do what Lowell said and check all pin5 and repair that part by soldering to the board as you suggested. Have you seen this problem occur in these connectors from the normal current draw alone or do I most likely have some sort of short going on? I'm going to check it regardless.

I'll report back on it later with pictures once accessed.

Chris

[g1]

It's not uncommon to have this sort of issue when heater current is run through those kind of connectors.

[Enzo]

Certain era Peavey amps had a problem with the heater pins burning on interboard connections. Bugera amps had this happen on the transformer connector, so they sent out a bulletin to just hard wire all of thm, and they immediately started hard wiring them in production as well. Hell I recall pinball machines in the 1970s has a problem with the lamp circuit pins in the same fashion. A couple hundred #47 lamps (same as in many Fenders) take quite a lot of current. designers have for years been underspecifying these type molex connections for high current supplies.

[drewl]

I've repaired this problem on these before.

I think it's best to solder the wires directly to the board.

Make sure to clean any burnt carbon or PC board material from the connector as it may cause a short.

Also check the four 1N4007 rectifier diodes for the preamp dc filament voltage.

I find them going bad and starting to burn the PC board around them in older units.

[clinkous]

Hello all,
I've removed the 4 el84 power tube board and checked for continuity between all pins 4 and 5 and nothing seems above 0.1 ohms. I am planning on taking up the main board to get to the underside this weekend and checking for burned/carbon marks on this board as well.

I like the idea of cutting out the heater part of the connector and direct soldering those two pins and leaving the rest to plug back in.

Any advice on the best was to do a clean cut on the molex connector? Razor knife with some sort of jig maybe or dremel cutoff wheel? Who's done this?

Will post pics with the main board up.

Thanks
Chris

[TimmyP1955]

Cut the connector body with one of these (which is a great tool to have around the shop): X-Acto X-Acto Extra Fine Saw Blade - XR-239

[clinkous]

Thanks for the saw info. Looks like a good one to have. Scored it with a scalpel and it fell apart being so brittle. Just going to file the burned plastic off of each side.

Catching hell trying to access the board without unsoldering lots of wires. I used a dental mirror to look and the underside of the connector doesn't look near as bad as the top.

I sanded the pins for the heaters and will solder them in the morning.

I also cleaned and retensioned the tube sockets paying attention to heater pins for preamp and power tubes.

What can cause an excess of heater current assuming it's not simply a connector failure? Any thoughts on this would be welcome before I power it up. No tubes in for first switch on?

Thanks everyone,
Chris

[lowell]

Usually a heater arcing issue is cause by an internal tube short.