Hartke HA5500

[Carlosraj]

eek! don't cut the trace lifting one end of R336 should do the trick!
as to relay operation i don't know(never been this deep into the protection circuit of a Hartke!) i'm hoping it would help determine if the fault is from the amp's operational condition or whether it's with the protection circuit itself.
i've spent a little time looking at the data sheet for the 7317 it seems to be a comparator of sorts and i'm unclear as to how turn on delay is acheived??


have you had a chance to check for oscillations?

Not yet.

 

[turk 182]

are you running/using a DBT on this currently?

 

[JMFahey]

Ok, now with some numbers we are starting the good path.

As mentioned above, a BEEFY power supply such as the one you have should not drop 7V each rail just from connecting a power amp board, even less if it´s already connected and just output relay clicks in.

A transistor Class AB stage "eats" very little at idle, a few mA, "nothing" compared to full power 10A or so.

BUT you say you messed with the bias trimmer and did NOT check idle current ... worrying.

You might have turned your power amp into a current guzzler which in due time might explain the protection circuit problems.

For now:
1) disconnect load (speakers/resistor/whatever) , work unloaded until we get proper DC values.
2) measure idle current, maybe schematic explains how to or suggests some values.
If none suggested, adjust bias so each power transistor passes between 25mA to 35mA each which should be a reasonable value.
To check current measure voltage drop across each emitter ballast resistor and do the Math.
3) not discarding oscillation as impossible, by any means, but suspect improper DC adjustments could be triggering protection, so get them in line first.

EDIT: what DBT asks.

 

[turk 182]

DBT = dim bulb tester or lamp current limiter

 

[Carlosraj]

DBT = dim bulb tester or lamp current limiter

I have put the amp aside first to fix my scope, it is malfunctioning. I will get back once it is done.


Thanks

 

[Carlosraj]

Ok, now with some numbers we are starting the good path.

As mentioned above, a BEEFY power supply such as the one you have should not drop 7V each rail just from connecting a power amp board, even less if it´s already connected and just output relay clicks in.

A transistor Class AB stage "eats" very little at idle, a few mA, "nothing" compared to full power 10A or so.

BUT you say you messed with the bias trimmer and did NOT check idle current ... worrying.

You might have turned your power amp into a current guzzler which in due time might explain the protection circuit problems.

For now:
1) disconnect load (speakers/resistor/whatever) , work unloaded until we get proper DC values.
2) measure idle current, maybe schematic explains how to or suggests some values.
If none suggested, adjust bias so each power transistor passes between 25mA to 35mA each which should be a reasonable value.
To check current measure voltage drop across each emitter ballast resistor and do the Math.
3) not discarding oscillation as impossible, by any means, but suspect improper DC adjustments could be triggering protection, so get them in line first.

EDIT: what DBT asks.

I could not get my scope done, but today I checked all the components, caps diodes, resistors, regulators on the power supply circuit, and they are OK. I noticed some differences on the power amp board, (A) both the thermistors are marked 50K on the schematic, but they are measuring about 15K, (B) R346, the resistor connected to the relay coil is 1.2K on the schematic, but there is a 3.5K resistor on the circuit. (C) Q303 gets very hot, but the other transistors around it are slightly hot. Adjusting VR302 (offset) does not make any voltage difference. Someone has worked on this amp earlier, so I will check to see if all the component values are correct. I have ckecked the zobel components and the components around the protection circuit, they are OK.


Thanks

 

[turk 182]

get any where on this?