Hartke HA3500 Direct Out Dead

[Fuzzynuts]

Hello all;
My Hartke HA3500 has no Direct Out signal. It worked for one gig but not the next one. During the night, every time that I plugged in to my bass after a break, there was a loud "Whoomf" from the PA system. The signal chain went from my bass (active electronics) to my pedal to the amp. The direct out went from the amp to the mixing board. Every volume knob/pedal was turned down to the minimum and the channel on the mixer was muted, yet this still occurred. The cabinet speakers did not make a sound. Every thing else on the amp works fine. No problems at all. According to the schematic, the direct out circuit is relatively simple. A couple of voltage divider networks, two op-amps all in series with the pre/post EQ switch. I'm going to check the switch first but if someone could give me a little direction as to what I could be looking for after that, I'd really appreciate it. Also, if someone would like to speculate on the causes, that would help to prevent it from occurring in the future.
Regards,

[Mark Black]

Not Hartke-specific, but I have seen the aftermath of that kind of thing before. I would speculate that either the phantom-power was on at the mixer and there was something in the amp that didn't like it, or there was a ground fault (mis-wired outlet or the like) between the mixer and the amp.

Look for puffed-up or exploded coupling caps at the direct out, and also look all around for burned traces at a ground connection. The opamps could certainly be hurt as well...

Good luck!

[Enzo]

I'd look at the output pins of that op amp - pins 1 and 7 - and see if either is sitting at DC.

Phantom could be a good call, turn phantom off and see if it still happens.

[Fuzzynuts]

Thanks

Thank you very much for all of your help. I'm going to jump into it next week (gig this weekend - not a good idea to rip your amp apart just before) and I'll post what I find and what the fix was.

Thanks again,

Leigh

[Fuzzynuts]

Hi all;
I checked the continuity from the pre/post EQ switch and it's OK. I have no DC on pin 1 of the op-amp and only 0.002 VDC on pin #7, which I assume is the equivalent of zero volts. I suspect that the op-amp IC is FUBAR. Is there anything else that I should check? All the caps look good. No burn marks anywhere on the PCB. Also, I can't find a datasheet for this particular IC. The markings on it are: 30678 5532 JRC. I know that the 5532 shows that it is a dual op-amp but there are so many variations in this type that I don't know which one is compatible. If anyone could steer me in the right direction, I'd really appreciate it. Thanks,

[Enzo]

It is a 5532. COmmon plain old op amp. I assume you want the one in a DIP. The various letters after the 5532 indicate package style - as in surface mount, DIP, SIP, whatever. The letters before the 5532 indicate the manufacturer, which is irrelevant.

ANy dual op amp will work there, slap a 4558 or a TL072 in to see if the chip was the problem. The 5532 is a lower noise part, but it ain't like the 4558s will sound like airplane engines. If that fixes it, then get the right part at your leisure.

COnect the DI out to an amp, now touch the input pins with your meter probe or a little screwdriever. This should inject some hum. Does this hum come out the DI? If so, the op amp is working.

[Fuzzynuts]

Update

As Enzo suggested, the op-amp is FUBAR. Probable cause was the sound guy pushing the phantom power button on the mixing board and giving me unneeded 48 volts. Thanks for all of your help.

[Fuzzynuts]

Update

FYI: Just thought I'd let you all know that the op-amp was gone. I put a 1kHz signal on the input jack and took a reading on the capacitor before the op-amp inverting input pins. I had a signal there but nothing on the output pins. I replaced the op-amp IC and tested again and found the signal was there. The whole operation only took a couple of minutes. Thanks for steering me in the right direction.
Fuzzynuts

[troncomobil]

Hi all. Seems there were many issues with this particular amp. I bought one at the pawn shop. Although the normal crackling sound was evident, I fell in love with it. It took me through one gig and died. I'm not much of an electrician but if anyone can help me with this problem, it would save me from dishin out cash for another amp which is kinda hard during these times. It started while playin my bass during practice and the sound would start to cut-off and then back on until it did not come back on at all. The amp turns on and off but no sound. Checked the cord and the speaker they were fine. So I decided to remove the input and output jack component and cleaned them with electronics lubricant spray. Let dry and placed them back on the amp. When I turned on the amp, the fuse blew. Rechecked connection from the jacks and again blew fuse. This is where I stopped. Something tells me that its time for another amp. Please help.

[52 Bill]

I don't understand what you mean by you removed the jacks and put them back.

In any case, it appears that you have caused something to short out the power supply of the amp. If you are lucky, it will just be a simple wire that you cut or crushed when you were working on the amp. If you aren't so lucky, then you may have done something that has caused real damage to either the power supply or the power amp circuit and the amp will need to be repaired by a tech.

[troncomobil]

Hi 52 Bill, The jacks i'm referrin to are the ones we plug in the bass and the speaker. I hav just removed the front circuit board and see no burn residue indicating a short. I did notice the top of one of the capacitors (50V 470uF) seemed a bit soiled like a dried up small leak not clean like the rest next to one of the two cans. Can there be a problem with the transformer? I really appreciate you helpin out.

[52 Bill]

There are many parts that can be shorted that will not look burned. What sort of test equipment do you have access to?