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1
Amplifier Discussion / Burned up cap
« on: November 07, 2019, 03:43:24 PM »
Hi. The forum has helped me in the past with amps but now I have a problem with a car radio and maybe someone can help me. This inexpensive car radio has had a capacitor burn up. It looks like it took out the 1000uf behind it too. I have plenty of 1000uf caps in my stash but I don't know the value of the burned cap. However, the cap around the other side of the 1000uf is a 104 (.01uf). Is it likely that the burned cap is also a 104? In my stash I found three different types of 104 caps. Which type would you suggest that I use as a replacement? Thanks.

2
The Newcomer's Forum / Re: Heathkit TA16
« on: May 10, 2019, 06:53:34 PM »
I have tried three times to upload a pic. Not sure what to do now.

Look here https://tinyurl.com/yyshve6g for a solution.

4
Here's an update. I ran across an HK195 repair video on YouTube where a fellow had a problem similar to mine. He found that the 3300uf 25v cap was leaking and replacing it solved the problem. My 3300uf 25v cap showed no signs of bulging or leaking, so I unsoldered and removed it for inspection. It looked like there was a small amount of residue on one of the legs right where it exits the base. I didn't have a 3300uf 25v in my parts stash so I replaced it with a 2200uf 35v. That solved the problem but I'm wondering if using that wrong spec cap can do any damage before the 3300uf cap I ordered is delivered and installed? Thoughts?

5
Unless those speakers hold some sentimental value it's hardly worth the effort

But, I know for a fact that every time I save some money and fix it myself an Angel gets it's wings.

Quote
...and keep the broken stuff as it's a source of spare parts...

Yeah, me too...

6
Measure DC volts at all 9 pins and post your results...

I also measured the ACv in case they mean anything. The converter output (AC to AC) measures 17.2 VAC

PIN     1      2       3       4       5       6      7       8       9
           
DCv    1     0.7    8.2     0.7     1       0     6.7   14.5   6.7   

ACv   1.6    1      17.2   0.9    1.4      0     14     31    14.1
.

7
Amplifier Discussion / Re: Looking for diagnostic help but it's not an amp
« on: November 06, 2018, 05:45:50 PM »
...If you take a look at the reference schematic on page 4, you can see an electrolytic cap C3 for ripple rejection. I would take a look at that one first...

I found the 22uf C3 and I de-soldered it and inspected it. No sign of leakage or bulges. I replaced it with another 22uf anyway then tested again...no change.

8
Amplifier Discussion / Re: Looking for diagnostic help but it's not an amp
« on: November 06, 2018, 11:41:11 AM »

...Does the device still pass signal or is the buzz the only sound it makes?What is the device on the heatsink? Would be helpful to have a reference schematic from the manufacturers datasheet...

The buzz is the only sound it makes and it is not controllable with the volume knob. On a whim I just measured 6.4vdc on the speaker output with the speaker disconnected.
Searching the web I couldn't find the schematic but I did find that the device on the heatsink is an output chip; an A2007A power amp IC. I found that info on this page that describes some of the components used:

https://www.staff.science.uu.nl/~tel00101/FotoAlbum/RadioCorner/Sets/HK195.htm

9
Hi, I've been lurking here for a few years and have enjoyed reading the repair topics and learning a little about solid-state devices. But now I find I need diagnostic help for a problem that doesn't involve a guitar amplifier. I'm hoping that someone can point me in the right direction with this non-amp problem but I will understand if this isn't the proper place to post. I just had my little powered bookshelf computer speakers go kaput. Suddenly and with no prior warning they started squealing and buzzing. And they do this even after unplugging them from the computer. The 15vac power supply tests OK and I don't see any obvious damage on either side of the board. I am going to include a link to a short video that resides on Google Drive so you can hear what I'm talking about.
https://drive.google.com/open?id=1mw1AzFlJktfG7W-b3fgpAxluKt4s-HGD

10
Amplifier Discussion / Re: Peavey VIP 2 buzzing/crackling
« on: January 19, 2018, 09:58:29 PM »
And when it does it, ball up your fist and whack the op of the amp.  Does that make it stop or pause the humming?
That's the first thing I tried at the gig when it started...no effect.
And, no difference when listening through headphones.

11
Amplifier Discussion / Re: Peavey VIP 2 buzzing/crackling
« on: January 19, 2018, 03:12:32 PM »
Thanks for the link. There is a 1/8in. headphone jack on the front. There isn't an effect loop or pre out, pwr in.

12
Amplifier Discussion / Re: Peavey VIP 2 buzzing/crackling
« on: January 19, 2018, 02:01:30 PM »
Thanks. I should have added that I've tried that along with trying different guitar cords.

13
Amplifier Discussion / Peavey VIP 2 buzzing/crackling
« on: January 19, 2018, 01:38:56 PM »
Hi...My Peavey Vypyr VIP 2 started buzzing and crackling a gig tast week. It reminded me of what it sounds like when a speaker is about to fail. When I got it home I swapped out speaker but the problem remained. Tried different guitars...same thing. After I turn on the amp it takes about fifteen minutes of warming up/playing before I can induce it to start buzzing. It is induced most easily when thumping on Bb or B note on the E string. Near the end of the clip I play a C note and the buzzing/crackling goes away. I have tried to attach a 1 min. 15 sec. sound clip:

15
In a series circuit, the resistor with the highest resistance will have the most dissipation. Calculate the current that will result in that resistor being at it's maximum, then check that the other resistors will be at or below their rating at that current.

In a parallel circuit, the resistor with the lowest resistance will dissipate the most power. Calculate the Voltage that will result in that resistor being at it's maximum, then check that the other resistors will be at or below their rating at that Voltage.

As a practical matter, running resistors at their maximum power rating is not a good idea. If they are on a PCB, it will usually make the board turn black. The resistor or it's solder joints will fail. A resistor's power rating is based on temperature. If they are in a warm environment, they must be de-rated. You can run resistors beyond their power rating for short amounts of time as long as the resistor does not get too hot. To be conservative, don't run resistors more than about half their power rating.

Thanks everyone.

.

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