Hartke HA 1400 Signal Issue

[Analog4life]

Picked up a sweet bass amp for cheap on CL. It's a Hartke HA 1400. Here's the problem . . . . When I plug into the input I have no volume. If I turn volume up all the way on the amp and the guitar I have extremely low volume (can barely hear it). If I plug into the return I have good volume but no use of the volume pot. If I plug in through input, put a jumper over C101 the volume pot works as it should and the volume seems normal but quite a bit of background noise and static. Not unbearable but I'd like to get it working as it should. Any suggestions? I'm new to electronics so hardly know where to start. I did replace C101, thinking that was the problem, and it worked normal for about 5 seconds. Thanks!

[J M Fahey]

Picked up a sweet bass amp for cheap on CL. It's a Hartke HA 1400. Here's the problem . . . . When I plug into the input I have no volume. If I turn volume up all the way on the amp and the guitar I have extremely low volume (can barely hear it). If I plug into the return I have good volume but no use of the volume pot. If I plug in through input, put a jumper over C101 the volume pot works as it should and the volume seems normal but quite a bit of background noise and static. Not unbearable but I'd like to get it working as it should. Any suggestions? I'm new to electronics so hardly know where to start. I did replace C101, thinking that was the problem, and it worked normal for about 5 seconds. Thanks!

1) measure voltage to ground on all 8 pins of IC101.
We expect around +15V on pin 8 , -15V on pin 4 and almost 0V (might find a couple mV at most) on all others.
Report any unusual value.
2) A node is where 2 or more parts meet.
Confirm that you have 0 ohm (meter might show less than 1 ohm which is its own internal resistance, thatīs acceptable) from jack ground to preamp ground, from jack hot to node R101/R127, and from each end of ribbon cable? joining AN1 to CN1 to the other end.
Connectors might be weak, pin solder might be cracked or tracks themselves might be cracked.
Also input jack solder pads might be cracked or loose, input jacks always get abused, cords yanked, etc.
Resolder dubious ones with a tiny amount of solder, just enough to refresh them.

I suspect either bad IC101 or cracked solder or poor connections, thereīs not much more there.

[Analog4life]

OK . . . . I was able to trace a signal using another amp from the input jack to IC101. Nothing past IC101. Checked voltage at IC101 and from top left going counter clockwise (see attached pic) I had -13V, -5.64V, -5.69V, -14.84V, 0V, 0.1V, -13.5V, and 16.39V. Think I need to replace IC101? If so, where would I get a replacement and will it be the same type or cross reference to something currently available?

[DrGonz78]

I bought some old chips from UTsource about a couple of years ago. Good prices and real genuine parts. NJM2068DD I think is the one you need...
https://www.utsource.net/ic-datashee...DD-941254.html

Edit: I thought the chip might be obsolete and was not something you would find at mouser anymore... NICE one!! Dude!! Let's go Bowling.

[The Dude]

http://www.mouser.com/ProductDetail/...4f4eLDBKG0A%3d

Edit: <simulpost> Looks like Gonz beat me me to it. Oh well, now you have options.

After you pull the IC, it's also a good idea to check voltages on the pads before installing the new one to verify there isn't something else wrong.

[J M Fahey]

Agree and add:IF you canīt get it or only sources are dubious EBay sellers, a standard TL072 will work fine there, no audible change in sound .

Pinout and function is the same, they used an Asian part because they are Korea based.

Confirm that you have 0V on all ICpins except 4 (-15V) and 8 (+15V, both nominal) before remounting it.

[Enzo]

And please learn how to count pins. Upper left corner is pin 1. Then 2,3,4 down the left, and 5,6,7,8 going UP the right. So 1 and 8 are at the top end. ICs have either a dot by pin 1 as yours does, or a notch at the 1-8 end. Really much better to refer to pin 1 or pin 2.

[Analog4life]

Thank you all so much for your help! Ordering the new one from Mouser today. When you say check voltages before remounting, you mean on the circuit board? Or on the op amp?

[J M Fahey]

On the solder pads, to check weird voltages are not coming from somewhere else.
Of course, the unmounted Op Amp canīt have any voltage on its pins.

[Enzo]

Right, pin 1 had 13v on it, which usually means the IC is bad, but it is possible the voltage is from the rest of the circuit, so when we remove the IC, then measure voltage on the solder pads to see if the 13v is still on hte pin1 pad or if it now has disappeared. That would mean the IC was causing it.

[Analog4life]

So I got the new op amp today. Started to pull the board out and made a new discovery that I hadn't noticed before. C415 is completely missing. Could that be causing some of my issues? I plan to replace this capacitor as well now. Wondering if I still need to plan on replacing the op amp too.

[The Dude]

That cap is a filter for the +15 supply. It looks like it was there at one time, so do install a cap there. I still think the op amp is/was bad because of the DC voltages on input/output pins. IMO, replace it.

[Analog4life]

Got the new op amp in and replaced C415 over the weekend. Works like a champ now! I can't thank you guys enough. I didn't test the pads before mounting the new op amp. Seemed like a lot of extra work. Thanks again!