No, we don't want to use 0.47 like I explain in post #155. It's important for you to understand that.
What year in EE are you at in college?
Heatsink question
- Thread starter Betomon
- Start date
What year in EE are you at in college?
Betomon
Active Member
Yeah I see what you mean, I left the originals alone. I just meant test as in, test to see if it smokes
I'm actually a mechanical designer.. Was studying for telematics engineering but dropped out of that and became a broadcast technician...then what I do now. I like electronics as a hobby. I'd like to understand it more though so I'm definitely interested in studying it on my own.
OK so the amp exhibits behavior similar to how it was at first. The bad board comes out of protection immediately, good board takes a few seconds.
Good board takes bias good, up to 50mv and doesn't overheat.. But its up there.
Bad board cannot get the bias above 12mv across R69 no matter how much I turn the VR.
R78 does not show proper voltage.. It goes up to about 2.4 mv max something like that. Something is definitely wrong there.
Same protection mode thing as before, it will trip the relay off if the volume is increased to a little past 25%
Already replaced Q14.. But something occurred to me. If these are npn PNP aren't they supposed to be matched? Meaning, if I replace q14, don't I have to replace q13?
Betomon
Active Member
Actually they are indeed in place. See the picture? The new big power transistors are connected
ghazzer
Senior Member
Betomon: When someone is offering you this much assistance you should work with them, step by step, unless you know more than they do. Taking actions outside "the plan" can do irreparable damage, or at least muck up the works. Alan has not completely shared his plan with you, but I suspect he is working it out on a post-by-post basis. After all, he has other fish to fry as well as helping you.
I'm doing some learnin' as well - - -
Good luck with your project.
I'm doing some learnin' as well - - -
Good luck with your project.
Betomon
Active Member
You're absolutely right. I thought Alan and I were on the same page since he mentioned "I think you're ready to put in the big transistors" or something along those lines yesterday.
But indeed I may have gotten ahead of myself a bit
Thanks I hope I can get it working right!Ha ha, talk about bigger fish to fry, I am stuck with my own amp for a few days on the spike due to the slow rectifier and I only have some luck taming it. I might have to order a fast bridge rectifier that is $25/pcs!!!! I have no room to play with other individual diode.....stuck with one style of casing!!.............
I tried to remember the old posts, but yes, my memory is fading too!!!!
Sorry, I forgot I did say you can put the big transistors in.
Measure B across Q7, adjust R36 and see how much the voltage change. You should get from 2.2V to 2.7V. Check that first, if it does not move then test the R36, could the trim pot be stuck at one value?
Betomon
Active Member
Don't worry I know this has been a lot of posts.. BTW I've been lurking on your thread about the 120 spike.. interesting stuff. My thought was that if it were harmonics, perhaps the trans needs some kind of damping?
Anyway I didn't get B on the good board, only the bad board. Only because this measurement was a bit awkward to do without getting dangerously close to shorting the transistor legs. I'll test both today after work
It would be nice to measure the voltage on both the good and the bad board. I have to have about 2.5 to 2.7V to make the output stage run. B has to have voltage of 4Vbe of Q11, 12, 15 and 16 PLUS the voltage drop across R69 and 79.
Now is to trace out why or where you lost the voltage.
Now is to trace out why or where you lost the voltage.
Betomon
Active Member
Yes just like you calculated,
The good board has 2.55V at B
Bad board has 2.13V with R36 fully CW
R69 and R78 still read low values. Can't get it past 12.8mv
Yet..if I pur the leads of my multimeter to the speaker terminals, I get about 85mV.
Doesn't that look wrong?
Good board gives me whatever I want across the resistors, right now it had 48mV and out of the speaker terminals it had almost zero mv.
Betomon
Active Member
Betomon
Active Member
Betomon
Active Member
Yes it does look strange.
Q7 is original. I haven't changed it but i have a replacement ready.
1ohm r30: 260mV
1ohm r31: 1.5V
162ohm r30 .79V
162ohm r31 .825V
I still cannot tell what's wrong. I don't think it's Q7.
I need you to measure more points. I updated the voltages according to your measurement. Take a look to make sure they are correct. The BLUE numbers is voltages for R34 is 1ohm. GREEN is for R34 is 162ohm.
The reading across R30 and R31 is not right, something seems to be wrong with the circuit before that.
Your amp is not easy to troubleshoot!!!!
I need you to measure more points. I updated the voltages according to your measurement. Take a look to make sure they are correct. The BLUE numbers is voltages for R34 is 1ohm. GREEN is for R34 is 162ohm.
The reading across R30 and R31 is not right, something seems to be wrong with the circuit before that.
Your amp is not easy to troubleshoot!!!!
Betomon
Active Member
I agree!Okay so there was some strange behavior when testing.. read on..
A: -85.6mV
G: .894V
E 1V
J 1V
L -263mV
F .91V
K -1.51V
H 2.15V
So, something interesting is going on around the A path. I tested by going to the leads of R44. If I test on the lead touching C13, it tests ~87mV. If I test it on the other lead, the one going to C22, it causes protection to come on immediately (audible clicking of relay and "standby" light comes on as soon as I touch the lead with my meter). The meter was hooked up to ground on the negative lead as usual.
I repeated that test on the good board, and, it shows 0mV at R44 by C13 side, and 23mV at R44 by C22 side.. and no protection. Something is very wrong in the bad board then?? But what??
For kicks I measured the emmiters of Q14 and Q13.. they both were right around -86mV - I did replace Q14 though. I suppose it's possible I screwed something up?
I just happen to update my own thread and saw new message popped up.
Is this for R34 = 1 ohm or 162. I need to have reading of both.
In normal operating condition, changing R34 should have absolutely no effect on A, E, F, G, H, J, K and L. But obviously the reading changed when R34=1 or 162. This is very wrong. So I need you to list out all the points for both R34=1 ohm and 162ohm to see what's wrong.
Is this for R34 = 1 ohm or 162. I need to have reading of both.
In normal operating condition, changing R34 should have absolutely no effect on A, E, F, G, H, J, K and L. But obviously the reading changed when R34=1 or 162. This is very wrong. So I need you to list out all the points for both R34=1 ohm and 162ohm to see what's wrong.
