Welcome, Guest. Please login or register.

May 28, 2020, 06:43:09 PM

Login with username, password and session length

Recent Posts

 

Author Topic: HH IC100 overheating BD711 transistor...help !  (Read 10872 times)

vintagekiki

  • Regular
  • **
  • Posts: 14
  • Chip Points: 1
    • View Profile
Re: HH IC100 overheating BD711 transistor...help !
« Reply #60 on: October 22, 2018, 11:57:25 AM »
The collector current that flows through TIP29/30C creates a voltage drop on resistors R29 / R33 = 33 Ohm connected between the base and the emitter of the output transistors 2N3773, and in this way provides the necessary bias for their operation.

Transistors for their work should have a voltage between the base and the emitter about 0.55 - 0.7V.

At low power transistors on PCB, ebc connections are near, so you need to be careful when performing measurements directly on transistors

Tip
For future reference when the power amp repair, replace the defective output transistor(s), the emitter resistor(s) of the defective output transistor(s), the both resistors of the base/emitter of the output transistors, the drivers if the defects are changed in pairs (TIP29/30C), check and adjust the idle current (25-30 mA per pair of output transistors).
Check the DC offset (≤ 100mV) of the speaker jack connector and that's it.

bobster

  • Regular
  • **
  • Posts: 35
  • Chip Points: 1
    • View Profile
Re: HH IC100 overheating BD711 transistor...help !
« Reply #61 on: October 22, 2018, 03:36:13 PM »
thanks Kiki , will keep all this info in my files for the future ;)

g1

  • Legendary
  • ******
  • Posts: 647
  • Chip Points: 77
    • View Profile
Re: HH IC100 overheating BD711 transistor...help !
« Reply #62 on: October 22, 2018, 06:10:13 PM »
The one voltage reading that stands out as odd to me in the faulty amp is the lower 2n3773 emitter which is reading approx - 47v on the faulty amp but reads 0v on the working one.
I may have mixed up the emitter and base readings but i don't think so as the wires are colour coded and connected to the same terminals on each power board which are apparently interchangeable.

Either way , on the working VS amp i am only reading approx - 47v on ONE terminal of the 2N3773 but on the faulty amp i am reading approx - 47 v on two of the 2N3773 terminals.....
...
am still mystified as to why the 2N3773 is showing two readings of approx  - 47 v when on my other working amp its corresponding transistor is only showing one..
You may have to dig in the probes more to get the reading on the Musician. 
The amp that is giving readings around -47V on 2 terminals is correct.  (should be roughly .6V difference between E & B terminals). 
If the VS Musician really measures -47V at emitter and 0V at base (of lower 2n3773), there is something wrong with it.

bobster

  • Regular
  • **
  • Posts: 35
  • Chip Points: 1
    • View Profile
Re: HH IC100 overheating BD711 transistor...help !
« Reply #63 on: October 22, 2018, 06:53:38 PM »
Hi G1 , yes you were right when you thought i had read the terminals wrong in the VS.
It does in fact have the two terminals reading approx -47v

On the IC100 i worked on earlier i am getting the slight voltage ~ 0.6v difference that you state between the two terminals B and E....

thanks again for all the tips i've enjoyed getting a little bit of insight into the SS world
rob


phatt

  • Legendary
  • ******
  • Posts: 2112
  • Chip Points: 254
    • View Profile
Re: HH IC100 overheating BD711 transistor...help !
« Reply #64 on: October 23, 2018, 08:39:41 AM »
Great to hear you got it working. :dbtu: :dbtu:

If you want to learn more about SS gear a good place to start is here;
http://sound.whsites.net/index2.html

I find the site map more useful for finding a particular subject;
http://sound.whsites.net/site-map.htm

You will need a long weekend and a month of sundays to get through all the pages.  :)
Phil.

sj-castle

  • Chipper
  • *
  • Posts: 2
  • Chip Points: 0
    • View Profile
Out of rehab into recovery
« Reply #65 on: October 24, 2018, 02:37:23 PM »
Out of rehab into recovery.
So the amp is working better than it ever has for us. It was gifted to my son 4 years ago but it had not seen much love in its life for quite some time before that, as it had been relegated to the garage, shed and who knows where else before we gave it a decent home.

Any how, this is what I did.
I could not measure any sensible continuity between the fuse posts so decided to replace them with some scrap I had kicking around. Not an ideal match but they work. As can be seen the corrosion was quite bad and I wonder how the thing actually work in the past months. With the fuses out I measured the no load idle current at 1.8A so something was up. I removed the cabling from the main TRs which all had ~0.4V forward drop across each junction which I guess is ok. The terminal post bolts were also replace due to corrosion while they were out.

On to replacing parts, I pulled all the electrolytics and tested them (get yourself one of the shown cheap testers if you don’t have such a thing). Both the 10v 47uF caps were dead and the 6.8 didn’t look too good, so I replaced them. The local electronics shop only had one 6.8. For the time being, the best of the two is back in for now (C6). I also pulled the 150pF which looked good showing 144pF on the tester so that’s back in. The only real problem is that possibly due to its hard life in some cold dark damp place the tracks/pads easily lift from the PCB when soldering.

The amp is now playing very well and loud, with no heating while idle.

My question is how hot does the back panel get when playing at volume, I know this is a bit subjective with out a proper reading, but it was quite warm after being played hard on stage setting for 10 mins or so. I pulled it from the cabinet and the two TIP drivers where more than warm but not burning to the touch (not uncomfortable and no smell)
would this be acceptable ?

... Simon

« Last Edit: October 24, 2018, 04:42:15 PM by sj-castle »

vintagekiki

  • Regular
  • **
  • Posts: 14
  • Chip Points: 1
    • View Profile
Re: Out of rehab into recovery
« Reply #66 on: October 24, 2018, 03:54:58 PM »
My question is how hot does the back panel get when playing at volume, I know this is a bit subjective with out a proper reading, but it was quite warm after being played hard on stage setting for 10 mins or so. I pulled it from the cabinet and the two TIP drivers where more than warm but not burning to the touch (not uncomfortable and no smell)
would this be acceptable ?

The best test of whether the amplifier overheats or not, is to follow the rear panel (heat sink) heating for 30 minutes without the signal (guitar is not connected).

The operating temperature of the rear panel (heat sink) without the signal should be slightly warm up to 30-40 degrees.
When the signal (guitar) is connected to the amplifier  and when playing a loud, normal operating temperature the rear panel (heat sink) is very hot to 70-80 degrees.

Tip
When examining passive components, be careful not to make a mistake in interpreting the measured nominal value and tolerance ratings.
The usual tolerance rating of most components is +/- 10-20% except aluminum electrolytic's which can range from -20% to as high as + 80%


https://www.google.com/search?q=resistor+and+capacitor+tolerance+rating
« Last Edit: October 24, 2018, 03:56:54 PM by vintagekiki »

bobster

  • Regular
  • **
  • Posts: 35
  • Chip Points: 1
    • View Profile
Re: HH IC100 overheating BD711 transistor...help !
« Reply #67 on: October 25, 2018, 10:10:50 AM »
thanks Kiki , that's good to know.....

Fwiw , i often put a small desk fan behind my amps at gigs , most of the places i play are low on space and the amps can end up pushed back against a wall and have little to no ventilation.

The fan is mainly for extra insurance to keep them cool as most of my amps are 40 years old plus lol

I also use lots of boost pedals etc and this can also cause amps to draw more power and put pressure on older components so by keeping them cool like this i have rarely had any failures over the years..
cheers
rob