Hartke 5000 Mystery

[Enzo]

SO if you have V+ all the way back to pin 6 of the protect IC.

it may be defective or it may be doing its job.  The 7317 is common ,look up its data sheet for the pin functions.

Lower right, see ACV comes in forms a negative supply with D309, C314.  DO you have that little supply?  That with a few resistors up to V+ form the reference voltage for pin 1 of the IC.  If that little 1uf cap is shot (hint) the reference is off and the whole thing doesn't work.

I don't usually encounter problems on the Hartke modules, but Samson uses the same circuit on their Samson power amps, and I often have issues with the 7317 circuit, which is almost always the small electrolytics are dried out.  There are like five of them there.

it happens, but the IC itself is seldom the issue.

[gbono]

Measuring from ground I have -48 v on the cathode of D309. I hate shot gunning boards but I did change out C314-18 and both the 470uF and 100uF caps were bad but the amp still isn't working.

Using ground for ref - assuming +-VCC are pins 5 and 9.

One side of R342 has -67V and the other side has -.7V.

Pin 9 of the TA7313 has +3.2V.

[gbono]

Okay back at this again - I think I have found a problem that is triggering the protection circuit. When I scoped the node between R334/336 I didn't see DC voltage since the scope was AC coupled  :grr With a DMM I have -15V at that point and the reason the circuit triggers. Where is the DC voltage coming from is the next question? BTW BOTH amps have this issue........

[phatt]

Both power amps?    Strange one for sure,,, maybe start by checking all the supply voltages and see if they are intact.
Phil.

[Enzo]

I don't recall we solved the grounding.  The modules are fully connected to the amp?  Both the large molex and the little input cable?  You report no continuity from molex to input ground pins on the board, but is there continutiy there with the module connected to the amp.  A missing ground to the input will cause DC offset.

[gbono]

Starting at the +-15 supply it looks like the center tap is ground connection which is carried to both amps via connectors AN101/101-1. I'll check these out. My PA boards don't have resistor 351 just a jumper and I will see where ground on AN101 travels on the board. I don't have the amps in front of me right now but it seems like the issue is either in the ground connection two each amp - connectors AN105, 101 and 101-1 or an issue with C406/407 both pos/neg voltage regulators were replaced. Hopefull

[Enzo]

You told me before I think that there was no continuity between ground connections on the two connectors.  But there needs to be, and it comes from the connections to the rest of the circuit.

[gbono]

Yup there is no continuity between ground on AN101 and CON501. I traced out the circuit and it doesn't match the schematic even though the board I have is 4005197001. Nothing has been changed on this board (actually both PA boards). Finding the correct schematic for this amp has been a real PINTA.

But how did this amp ever work?

[Enzo]

OK, so each connector has a ground connection, or should have.  Which one is not showing continuity to the rest of the circuit, ie chassis?

[gbono]

Yes I will check this out when I get back to this amp - I'm assuming that the center taps of B+-, grounds on connectors  CN501A/B, AND grounds on connectors AN101/101-1 should all be connected to chassis? BTW this rev of the PA PCBs do not have a connection (ground bus) between AN101 and CN501 and ref designator R351 is loaded with a jumper and connects R321 to the emitter of Q310.

[Enzo]

HOW they do it really isn't the issue, whether all on the power amp board, or spread through the amp.  What does matter is that the inputs and outputs all need to consider the same frame of reference - we really don't want the preamp to consider ground as +4v and the power amp thinks ground is -22v.  SO when the amp is assembled and whole, the input to the PA needs to consider ground the same as the output stage.  In most cases that will be chassis.  If the speakers think chassis is ground, then so should the PA input connector.

I made up the numbers, don't go looking for -22v or +4v.

[gbono]

Soooo embarrassing 

There are 4 screws that hold the preamp board to the chassis -  2/4 the screws I did use had a clad pad that made contact, via the screw head, between the top of the board to  chassis connection so I thought I had a chassis ground. What I didn't know was the 2 unused screws and their clad pads were the screws that supply the connection between the center taps, PA ground, etc. etc.   Live and learn.

[phatt]

well if it makes you feel better I've made that mistake before,, :duh
I've banged my head against a wall a few times over the years for similar fluff ups.
Phil.

[Enzo]

My first encounter with a missing ground was some Yamaha power amp.  I determined the PA was bad, preamp OK, so I disconnected the preamp signal.  I fixed whatever had been wrong with the powr amp, blown outputs or something, but spent a coule hours trying to figure out teh DC offset issue.  Finally reconnected the preamp cable, thus restoring the ground to the front end of the PA, et voila, all better.  I have never forgotten since to always make sure the input has a ground connection.