Hartke HA 3500 Transient attack

[catstrat]

Hopefully a schematic will be following shortly. This amp took a nasty fall and hit on the front panel and destroyed all of the control pots I replaced the damaged pots and repaired the soft start relay circuit. It powers up but has no output. The voltages are correct at the output transistors and i'm getting signal to the o/p transistors and signal out of the transistors but no output at all at the speaker. I'm thinking it's the relays on each of the output boards. The relay coils connect to a 9 pin chip which i think is the output protection. The hi voltage rails are good. Let me see if i can post a schematic. Thanks

[catstrat]

Let me revise this. I'm getting a strong signal into the bases of the O/P transistors, a signal at the emitters but nothing out of the collectors. I have voltage at the collectors + 71 and - 71 volts respectively. Tried to post the schematic and started to drag the image and it didn't work. I'll keep trying. I have to get familiar with this. Thanks.

[Jazz P Bass]

There are a number of versions of this amp.

See if you can find a version number on the PCB.

The protect IC's may be doing there job.
What Vdc do you measure on the output transistor emitters?

If you have base signal & emitter signal (there will not be a signal on the collector) then the next step is to check the protect IC output.
If the relays are getting turned on, then the contacts inside may be bad.

HA-3500_1.35.zip

Ha3500a.zip

[catstrat]

Hartke

Hi Jazz P. I'll have to check the emitter voltage but the scope shows both emitter and base signal to be about the same strength. I'll verify this tomorrow. I heard there were 3 versions of this amp so I'll try to find that out tomorrow. I don't know how different they are. The fall it took was a pretty nasty. As expected I get a good signal from the effects loop send. Used a patch cable to jump the effects loop and that didn't work but come to think of it, I heard a very low volume sound at the speaker when I turned the master volume. I'll try to find out this other stuff for you. Thanks.

[catstrat]

Hartke

The numbers on the pre amp board are 4005 198 011 along with 3500b, 5000 , 7000b. I hope these are what you're asking about. Thanks.

[Enzo]

Get a grip. The output stages of a SS amp are current amplifiers, not voltage amplifiers. It is normal for the signal LEVEL to be the same on base and emitter there. As to not seeing signal on the collectors, well really, since the collectors are wired to the power supplies, we wouldn/t expect signal there.

You can upload schematics or you can link to them if they are already online.

Either your relays are broken and cannot pass signal, or they are not being energized. Find out which.

[J M Fahey]

Just to test and confirm the excellent advice upstairs:
1) measure DC voltage between the speaker out "rail" (the track where power transistor emitters go, usually through low value wire resistors) and ground, no signal applied.
If you have less than 200mV DC, it's safe to direct connect to speakers.
If higher, then the 9 pin IC is detecting that and not enabling the speakers ... that is its job, in that case you must solve that problem first.
2) IF safe, grab a jack with two wires, solder ground to PSU ground, solder hot straight to speaker rail, plug a speaker, test (plat some music).
NOT "a repair" , just a test, if amp works now you know that the relat/protection is your problem.

The 9 pin IC is relatively common, it's popular in rice_and_chopsticks powered amps

[Enzo]

The TA3173 or 7137 or something?

I have maybe had one of those ICs bad over the last 30 years. problems with it are almost always the little electrolytic caps associated with it.

Of course it could just be doing its job, and leaving the relay off for a reason.

[catstrat]

Hartke

Thanks Enzo for explaining about the collectors. Again I don't work on a whole lot of transistor stuff and they confuse me in certain ways. I always thought the collectors were like plates on tubes. This is where I need help at. But anyway, turns out the schematic I have is wrong. I'm thinking the fall this took has something to do with it. The next thing is to look at the right schematic and go from there. Expect more questions to come soon, at least before I heave the thing into Pensacola bay.

[catstrat]

Hartke

Thanks Juan.

[Enzo]

The output of a solid state amp is emitter followers, just like cathode followers on a tube amp. In a cathode follower, the plate connects directly to the B+ rail, and we do not expect any signal there either.