Blown Transistor on Hartke HA1200 (hs-1200 board) for Kickback 12. Any advice?

[Nobail]

Hi Folks, - First Post.

TLDR: took apart my amp and now a transistor has blown. How to fix?

Do you like stories? I hope so.

I have a Hartke Kickback 12 with the HA1200 amp. I bought it used and it worked fine for a few years, with the exception that jack sucked and I constantly needed to fiddle with the cable to get sound and deal with lots of crackling. After the problem worsened, I decided to replace the jack. So, bought a replacement off the internet, and off I went.

So, unfortunately, I didn't research anything and just dived in to disassembling the amp. My first mistake was removing the heat sink from the board. This was not required to get the board out, but I didn't know, removed all the screws and unfortunately took it off. No worries, I thought. I have thermal compound, so I'll just clean it, put on new compound and replace the heat sink. Easy Peazy. However, if I had done a little research, I would have seen this was not necessary. Lesson learned, I hope.

So, I replaced the jack and turned my attention the the heat sink. After cleaning the transistors with alcohol and cotton, I then started to wipe off all the gunk off off the heat sink. Much to my surprise, there were some plastic rectangle pieces on the heat sink embedded in the gunk. I though, that's weird. Why have those there? That can't help the thermal transfer. Anyway, i just removed them. I am guessing that is my second mistake. I then put new thermal compound on the transistors (MG Chemicals Silicone Heat Transfer Compound) and reattached the heat sink.

I then reassembled the combo amp, plugged in my bass, turn it on and tried to lay down some awesome riffs, and nothing.... no sound. So, I thinking about what could have gone wrong. Did I f-up my soldering for the input jack? Then, I hear a pop and see a spark come from inside the amp and smell something burning. So, I unplug and disassemble again (not removing the heat sink this time). So, I can see one of the transistors has blown. I'll attach a pic if I can.

So, now what? I am guess that the plastic film pieces are parts of the transistors that pealed off and stuck to the heat sink. If I replace them all the transistors that were in contact with the heat sink, would that fix this issue? Is it likely other parts are blown now? Is this even salvageable or should I just get a new combo amp? I am thinking it could be fixed, but not sure.

Looking at a HS1200 schematic I found on this forum (the AMP is a HA1200, but the board says HS-1200), it seems the part to replace are:

Q217 - B688A
Q211 - A968
Q215 - B688A
Q2 - (Part not marked on schematic)
Q1 - D718
Q214 - D718
Q210 - C2238
Q216 - D718

Any advice on the way to proceed would be appreciated. Should I just order a new hs-1200 board from Hartke (do they even do that?). How is their support? Should I call their support and discuss my options? Should I attempt to replace the transistors? Note: to date, I have only ever replaced pots and jacks.

Thanks in advance for any help or advice.

Regards
-Hal

[Nobail]

see pic of blown transistor.

[Jazz P Bass]

The 'back' of each of the transistors NEEDS that mica isolator.

It 'isolates' the + & - high voltage rails from each other.

I hope you are good at troubleshooting a blown dc coupled class AB solid state amplifier.

If you can, post the schematic or a link to it.

[Nobail]

Thanks for the reply. I still have that mica film if that helps. Is normally, the film attached to the transistor? Is it typical that it can peel away when a heat sink is removed? Can I reattach it or once it peels away is the transistor ruined?

No, I am not good at this, but like to tinker. I do have a multimeter if that helps.

I have attached the schematic (I hope, first attachment).

Thanks again for the help.

-Hal

[Nobail]

So, took off the heat sink and looked at all the transistors on the board. They are:

6 larger ones (that look the same size as the mica film)
3 x C5197 (Toshiba - also have 0 4A n them)
3 x B688A (large K on them and 0 3B)

Two smaller ones (no film?)
1 x C4370A (Also K and Y 343)
1 x A1659A (Also K and Y 332)

I'm guessing all the larger ones will need to be replaced, but really have no idea.

-Hal

[Enzo]

The mica washer is pinched between transistor and heat sink, the way a paper place mat is pinched between table top and your dinner plate at a restaurant.

You grease the back of the transistor, and also the heat sink, then mount the transistor to the sink with the mica washer between. it insulated electrically the live rear metal surface of the transistor from the grounded heatsink.

[Jazz P Bass]

Does your meter have a 'diode check' function?

That is the ideal way to check a transistor.

Look up the datasheet for each transistor.
Put a "2S" in front of each number. (ie: 2SC5197)'
That will supply you with the pinout diagram.

The big boys are in parallel for each specific part number.
So you may need to remove them to check them properly.
(look up "transistor testing with a multimeter")

[Nobail]

Hi All,

So, it appears my little mistake is going to be very educational. Watched a few videos yesterday, including a hour documentary on the transistor.

My multimeter has diode testing and hfe testing (which I guess could be helpful, not sure yet). It is actually a "multitester" with lumens, humidity, temp, decibels and a multimeter.

Since I am not in a hurry, I will remove the transistors and test them. However, as the weekend is over, this may take a few days. In the mean time, perhaps someone can answer a few questions?

1. So, I assume I shorted out the transistors because of the film absence. Any other likely consequence of my action? Any other parts I should check?

2. Since my transistors were shorting, would this explain for my lack of sound?

3. Is it likely any of them have survived?

Thanks Again.
-Hal

Thanks
-Hal

[Jazz P Bass]

The output transistors are the source of the current that drives the speaker.

If shorted, all sorts of bad things can happen.

First off, build a lamp limiter.
Google it.


Do as Enzo points out.
Print the schematic & highlight parts that you find bad.

Working backwards from the output, I would suspect the drivers, Q10/ Q11.
The bias transistor would be next in line. Q209.

The limiting transistors, Q212 & 213 take a hit sometimes.
They can be removed & tested.
The amp does not need them for testing without a signal.
They can be put back when you get the thing running.

All six 5 watt ballast resistors, R1/ R2....., should be checked.
They go open on failures like yours.

Any resistor really, that is associated with a blown component should be checked.

[jasonsjwou]

New to the Forum, sorry I joined to seek some help on troubleshooting.
Again, sorry for reviving an old thread.

I have a same Bass Amp, with an issue. It's not working properly.

1. It powers on.
2. When the volume is turned all the way to MAX (and a bass guitar connected), I hear a faint but definite bass sound coming out of the speaker.
3. When a headphone is plugged in, I hear the same "faint" sound that's coming out of the speaker.
4. When connected thru DI OUT (to another mixer), I hear the same "faint" sound as #2 and #3.

I'm not an expert at reading a circuit diagram, but I did download the HS1200 circuit diagram.
Tracing from the input... Could it be the "IC101-A" the "JRC072" OpAmp that's faulty? because the output from DI OUT is same.

Any heal greatly appreciated... Thank you!

[Enzo]

Hi, welcome.

The thing to do is start a new thread for your amp. This thread has been dead for three and a half years, and it is about someone else's amp anyway.


If the DI is real weak too, then yes, the first stage is suspect. That is the very common TL072, the brand doesn't matter. You could try a swap. But it could also be a bad or disconnected C102. Us a small screwdriver,, or unbend a paper clip, or even just hold piece of wire, and touch it to pin 3 of that IC. Does that produce a good him signal? Or is it real diminished too?

[J M Fahey]

Welcome and please start a new thread telling YOUR own problem.