Intermittant problem with Hartke 7000 Bass amp

[TransLucid]

I'm working on an older Hartke SS bass amp. There is a main preamp board and two power amp modules, all connected (with the PT) together using plug-in connectors. There are headers on the pcb with prongs sticking out of a nylon base that mate with crimp-on connectors mounted in a nylon housing. The connectors have different numbers of connectors (5, 8, etc.).

The problem is the connectors are not making reliable contact with the pcb-mounted pins. I've cleaned everything with contact cleaner, but it seems like the connectors are loose, so when the amp is vibrated or tapped the contact comes and goes.

Has anyone else had this problem, and if so, how did you fix it? I suppose I could try to find new connectors to replace the old ones, but that may be difficult. Does anyone know where to get them? Is there another way (for example, removing the connector pins from the housing using some tool and tightening the connector by squeezing it with pliers)?

Any helpful advice will be appreciated.

Bob

[g1]

You mentioned cleaning the connectors but have you resoldered all of them? That was a very common problem when those amps were current.

[TransLucid]

I didn't resolder the pins to the pcb, but I did inspect them closely and they look fine. I intend to do that before I reassemble.

[TransLucid]

By the way, would you pls. describe the solder problem as fully as possible (was it just the connectors or every component, etc)? Do you recommend that I touch every joint on the pcb?

[g1]

Depending on how old it is, if it's lead free solder you can't really see if a joint is bad. That's my biggest issue with lead free solder.
If the solder isn't the problem, you will probably need to replace or hard-wire the connectors. Also, putting a bit of a bend or kink in the pins (or even thickening them with some solder) might do the trick.

[g1]

Sorry, missed your other response. It was usually just the connectors that needed resoldering. You shouldn't have to resolder everything.

[TransLucid]

tnx for the good suggestions. Is it just the connector pins (maybe some kind of reaction between the pins and the solder) that could be intermittent, or is it all the solder joints? I did hard-wire one of the connectors (the two wires to the power amps) , and found I could pull it out of the board without unsoldering it, supporting your contention.

[Jazz P Bass]

That is going to have to be a call when you flip the board over.
Take a look at the largest components.
If the solder is not wicked up (like a Hershey Kiss) you may have to touch them up.
Also look from one side of the board to the other. If one side "wicked" good & the other side did not, that is the area I would resolder.

[Enzo]

The Hartkes are generally well built, but if there is anything like a consistent problem, it is failed solder under that row of male pins along the back center edge of the main board, where the transformer leads come in. Flip the board over and resolder the entire row of them.

That really is far more likely than the female pins losing their grip.

Obviously anything is possible.

[TransLucid]

Enzo -

I did as you suggested, and the preliminary results look good. I think there's something about the chemistry of the pins and solder they used that causes the connections to open. I pulled another header out the board when I disconnected the lead to the power amp...

Now, I need to see how it will hold up in use...

tnx
Bob

[Jazz P Bass]

I would think thermal conductivity before chemistry.
One of the processes of production wave soldering is a step called "preheat".
The titanium rack, filled with multiple circuit boards, must be preheated.
The larger components take the longest time to heat up to proper temperature.
This takes time.
The enemy of production.
So if the boards were not preheated to a high enough temperature, Wallah.
A bad solder job.
The board works, it passes inspection (how, I do not know), a few years, a few hard bumps, the amp "fails".

[TransLucid]

That's a reasonable theory, but, given the fact that it's usually the connector headers that fail, I think there may be a stress-related factor as well. The connectors are bigger and heavier, and the cables attached to them get jostled, so they move around more that other components, which may loosen them up in the pcb.

[Enzo]

Yes, my vote is the vibration and motion of the wires pulling the females back and forth on the male headers breaks their solder. CHemistry does not sound right to me. In this modern era of lead free solder, I;d believe it, but in an older Hartke with lead solder, not likely in my view. Of course, I could be wrong.

[TransLucid]

One last potential cause: high currents. I noticed that the filament supply for the preamp tube went out first, and that draws a relatively high current.

By the way, what's up with this site? I keep getting "attack site" msgs...