SoundTech 6150 Powred Mixer

[cbass]

Ok I have +15 and -15 from the bridge rectifier But Q117 and Q118 Have about 12-13 volts across the C,B and E.

[Jazz P Bass]

I don't know about those readings.
I would think more like 20 Vdc from rectifier.
Zener regulated 15Vdc at the base of Q117 (-) & Q118 (+).
That would give 14.3 Vdc at the emitter output.
Where these readings taken with the ribbon cable to the preamp disconnected?
That is what I would suggest.
Here is a pass regulator link: Series voltage regulator

[cbass]

Thanks Jazz R104 was open and R152 was way out of spec so replaced them.I've got + and -14.3VDC coming to the wires on the connector while its disconnected.After I connect the cable I am seeing about 10VDC at the same place

[cbass]

Doh! I stll had my bulb limiter hooked up.I now have right at 14VDC at the rails now.

[cbass]

FIXED!

WOrks now! THANK YOU! You guys are the best.

[cbass]

Ha I spoke to soon.So I hook up my MP3 player.After playing it for about an hour or so at fairly low levels.Boom fuse pops.So I replace fuse hook up current limiter.34VDC on the speaker jacks.At least It popped the fuse instaed of my speaker.After I thought about It. I remembered the speakers I had hooked up to are 4ohm.Is this thing not going to handle a 4ohm load?

[Jazz P Bass]

Playing the amp at low volume should not have anything to do with 4 ohms.
Back to sqaure one.
Look for shorted output transistors, drivers.
Open resistors, open diodes.....

[cbass]

Do you think this amp will be able to handle a 4 ohm load once working properly?If not its worthless to me.Its already takin out a $100 driver.I want to be pissed at my bandmate but its my fault I guess.

[Jazz P Bass]

Here are the specs.

SoundTech 6150 Hgh-end PA 6CH AMP Full EQ, Reverb. Will make for a solid powered mixer for band practice or even for playing out in small halls or rooms, in club situations. Nice sound quality and it really is a powerful amplifier/mixer. Made in the USA, Buffalo Grove, IL. Some features/specifications of the mixer include:

AC input: 220V, 50Hz, 300W

H=220mmxW530mmxD330mm Weight=15Kg

MAIN CONTROL:
MAIN LEVEL
REVERB LEVEL
9 BAND GRAPHIC EQ
MONITOR LEVEL
EFFECTS LEVEL SEND & RETURN
AUX RETURN

INPUTS: PWR AMP/AUX/CD&TAPE LFT&RT
EFFECTS/GRAPHIC.

OUTPUTS: MAIN/MONITOR/REVERB SWITCH/EFFECTS/GRAPHIC

EACH CHANNEL:
HAS JACK & XLR INPUT, LEVEL, MONITOR LEVEL, LO & HI EQ, AND REVERB EFFECT.

REAR PANEL:
SPEAKERS OUT LT & RT(8ohms)/POWER SWITCH

Frequncy Response: +0 -1dB 15Hz to 20KHz (150W RMS 4ohms)

Rated Power & Load: 110W RMS 8 ohms, 150W RMS 4 ohms

Total Harmonic Distortion: Less than -0.05% (150W RMS 4 ohms 15Hz-200KHz)

[cbass]

thanks, I'll tear it apart again here after while and see what I can find.

[cbass]

Looks like all the power transistors on one side are shorted out.I'll see what else I can find when I have some more time.

[km6xz]

Tough luck, after all that work. It the output are shorting, there is something else wrong that was missed the first time. Without a load, until it is fully stable, check the current flow through the emitter resistors when you run the power amp section again. Was there any heat problem, too much heat while running at a low volume for example? It the speaker known good, did it sound normal while playing while it did play?

The driver transistors will generate a centered(zero offset) version of the signal at the output if all the output transistors are pulled. To save expensive power transistors, don't put new transistors in until you can verify that the driver transistors, differential amp and signal shifting(Q104) are stable and working correctly. Do you have an oscilloscope you can monitor the output signal with? If not, a line input on a small monitor amp through a divider network or pot so you can prevent overload and still try to get a good output swing out of the speaker jack.
You mentioned Q104 possibly had been installed wrong. Check that carefully, it can cause either high distortion or high collector idle current if wrong.

[cbass]

No I don't have an O-scope I need to get one.The speakers are good .It sounded fine up untill the moment it blew.It wasn't hot at all.I'd like to get this thing working to have for practice but its really startin to piss me off.I'd like to set it out in the back yard and blast it with my 12 Ga.

[KerryOkie]

That is a strange reading. Pull the IC and turn it on again to see if both the positive and negative 15volts are present and stable at pins 4 and 8. If they are, replace the IC, and if not, you have only a few components to consider, the caps and Zeners

I'm kinda having same problem on my 6150.
I was given amp and at first didn't hear any out put. But turning up any inputs i could hear a little output.
I measured between pin 4 & 8 on ic with and without pre amp cable and it measured 30 vdc.
any help would be great.
Kerry

[Leo_Gnardo]

I'm kinda having same problem on my 6150.
I was given amp and at first didn't hear any out put. But turning up any inputs i could hear a little output.
I measured between pin 4 & 8 on ic with and without pre amp cable and it measured 30 vdc.
any help would be great.
Kerry

Best to start a new thread for your problem if the following advice doesn't help. Be aware first that the number one cause for signal-gone-missing would be faulty normalling at the power amp input jack, years of corrosion bring this on in many amps & mixers. Simply exercising the connection, iow stick a plug in, pull out, repeat several times - is often enough to restore proper operation. And if that works you'll feel like a genius. For a while anyway...

MOJO published a tech tip about this.
The%20Dreaded%20Switching%20Jack%20Problem.pdf