Buttkicker Class D troubleshooting with scope measurements

[mikeskory]

I'm troubleshooting a straight forward Class D mono amp. I'd be happy to upload the schemo if somebody wants to help me understand the TL074cn comparator circuit. The amp was blowing fuses and many parts toasted. I have replaced the 4 high side FETS plus 6-8 electrolytics on that side. It lights up now and 'turns on' with an audio signal without shorts or overheating. But...no sound. It has audio going in to this TL074 IC comparator. I'm pretty sure its bad but I want to know how to test the outputs of the IC first.

[The Dude]

Well, yes, if you can upload a schematic, we can give it a shot. Otherwise, we're just guessing.

[nosaj]

I'm troubleshooting a straight forward Class D mono amp. I'd be happy to upload the schemo if somebody wants to help me understand the TL074cn comparator circuit. The amp was blowing fuses and many parts toasted. I have replaced the 4 high side FETS plus 6-8 electrolytics on that side. It lights up now and 'turns on' with an audio signal without shorts or overheating. But...no sound. It has audio going in to this TL074 IC comparator. I'm pretty sure its bad but I want to know how to test the outputs of the IC first.

https://www.electronics-tutorials.ws...omparator.html

This next link should be of help with testing it in a jig circuit. But with it being such a cheap part..
nosaj

http://www.diyaudio.com/forums/analo...-tl074-cn.html

[Enzo]

Hi, Mike.
I dropped by last wednesday on the way by, but you had already left.

DO you have a working PV mixer from the 1980s or early 90s? Or for that matter any number of their SS heads? They used TL074s a lot, and they socketed the chips back then. Easy enough to sub yours into that old PV for a test. Seems to me you usually have some old Peavey sitting around back there.

The TL074 is pretty much just a pair of TL072 in one part. The four outputs are the corners.

We looked at that amp briefly, it looks like an amp alright.

In some amps the TL074 might be used for audio, but sometimes a section might be used to drive a peak light, or to control a limiter.

I don't recall, is there a speaker relay? If so, does it click on?

Yes, a schematic will help.

[mikeskory]

Nosaj! I'm sorry it's not the parts cost. I have them in stock. I'm trying be more thorough in my diagnosis before I break out the soldering tools. For this unit and also for future units. And thanks for the article!

[mikeskory]

Hey Enzo! The TL074 IC102 is there to create a square wave for the 2 FET driver ICs. (I think) Here's the schematic...

[mikeskory]

Hey "the Dude"! I included the schematic in the original post and I'll try to upload it here to.

[Enzo]

OK, there is a speaker relay, does it click on? DO you have both LV power supplies, I assume 15v?

What are the two little driver ICs?

TL074? I see the input going to pins 9 and 13. The pin 13 feeds the upper side driver IC through Q2 via pin 14. The pin 9 outputs and inverted signal for the pin 7 section, which feeds the inverted signal to the other drive IC via Q1. Not exactly sure what the pin 1 group is up to.

This is a bridged amp, neither side of the output is ground. Do not ground your scope to either speaker terminal.

[nevetslab]

Buttkicker BKA 1000-4A Service Manual

There are four of these Buttkicker BKA-1000-4A's in our Drum Dept inventory, along with the Buttkicker LFE Drum Thone Shaker motors that mounts to the drum stool to vibrate your seat like nobody's business.

The system works well, when it is working, but seems like it takes a dump too often. Not specified on the schematic is the IR2111 Half-Bridge Driver IC (IC1 & IC5), which often fail. Also on the back side of the Class D PCB are surface mount 2SA1015 PNP xstrs...I had a lot of those fail. as well as the IRFP250N MosFET's. I have had TL074's fail, but not often. The extra-long DPDT toggle switch that protrudes thru the front panel also takes a whack and breaks. Those you can't find in inventory from distributors. And, for some reason, the bi-color LED's fail.

I've attached the Service manual, the Instruction manual and the manual for the LFE shaker motor

BKA-1000 Sch Pg 1.pdf
BKA-1000 Sch Pg 2.pdf .
BKA-1000 Sch Pg 3.pdf
BKA-1000 PCB's Pg 1.pdf
BKA-1000 PCB's Pg 2.pdf
ButtKicker_LFE_User_Guide.pdf

[nevetslab]

Here's some additional component information from repairing these amps. When I came across some shorted 2SA1015 SOT-233 SMD PNP transistors, I found my choices were buying them on ebay (parts no longer available new), or find a suitable replacement. I ended up using BC856 PNP's that were similar enough in characteristics. I've attached the data sheets on both parts. I also attached the data sheet for the IR2111 Half-Bridge Driver IC.

2SA1015-SOT23.pdf
BC856-860 PNP SOT23.pdf
IR2110.pdf

[mikeskory]

Thank you! I could only work for a bit today because of an out of town gig. Here's where we are: I replaced both IR2111s. I also had to replace Q13 because I nicked it with the dremel while cutting the leads in the IR2111s. I was impatient pulling the stubs out of the board so I had to run jumpers from Pin 2 of each IT2111 to the collectors of Q13,14. BUT IT PLAYS and sounds clear. I have a problem now when I turn it up either by it's volume or give it too much input. The sound cuts off (not the power/turn on lights). If I switch it off, count to 10 and turn it on it's ok. I'm hoping it's my connections to the IR2111s. I'll let you guys know tomorrow. The problem seems to be at pin 2 of IC5. Very little square wave input. IC1 pin 2 seems to be good. So I'll pop the board back out and take oms measurments

[nevetslab]

I forgot to include the Power Amp PCB page, and have that to add to the service documents on the Buttkicker BK1000-4A. Also adding the Output Protection IC type uPC1237A.

Buttkicker Pwr Amp PCB.pdf
uPC1237HA.pdf

When youhave the amp powered up, what are the DC output levels on the two halves of the Bridged Amp? Normally, with everything running ok, the DC output level is less than +/-60mV. , and less than that between the two amp halves (as you would see on the output binding posts). The AC Mains current @ idle was around 110mA @ 110VAC. I thought I had more AC Mains readings, but in reading thru my service notes, I had failed to record that. I forget where the Output Protection circuit is set at which point exceeding it would cause the output relay to open (on one of the two amp outputs). But there's details on how to set that in the uPC1237HA Data sheet.

I see in one of the units I was working on, going thru the RCA input jack, I wasn't getting normal signal level like I was getting going thru the 1/4" input jack. And, driving the amp into clip produced a nasty high-pitched buzzing sound mechanically from the amp. And if you switch the front panel Low Pass Filter out, you'll see a lot of square wave output, whereas the LPF cleans up that output signal a lot. We always have it switched in.

As you no doubt know, this amp is a low frequency power amp designed to drive the small 'shaker motor' that gets attached to a drum seat or even an elevated/isolated small platform so you can feel it when standing on it. Usually we'd feed kick drum and bass to it. Only the lowest octave on Bass works. Definitely works with kick drum.

In my shop, I have a Roland V-Sessions TD-10 controller that I've used to drive things like this amp/ & drum stool shaker, as well as a 1/3 octave pink noise generator, that I will set for 40-80Hz, which produces random-amplitude LF sine wave.

When your amp stops giving output, see if it's still producing signal on the amp-side of the protection relay (which is only on one of the two amp outputs). I don't show any instances in my service notes maintaining the four Buttkicker amps ever having that problem. So, that's uncharted territory for the moment.

Changing out blown MosFETs....the plate-thru on the PCB tends to fail way too easily, forcing you to have to solder them back in on both sides of the PCB.

[mikeskory]

Ok we have it playing. These are the parts I replaced. 4 IRFP250n FETS, 2 transistors Q13.14, fuse, 11 electrolytics in the high side of the amp. (same side as the bad FETS), 2 IR2111, 2 ceramic caps. Plus, jumping the print I buggered at the ICs. I think everything was truly bad except Q13,14. On to new adventures. Thank you everybody and especially thank you for the links with educational articles. Mike "Dean of Decibels"