Good evening.
I planned on getting out of this hobby, mostly due to lack of time for building and learning.
So, I thought "why not make a pre amp and a simple power amp and leave it at that?".
I decade or two ago I build Greg Balls GB150 and for some reason I sold it.
I managed to find old kits for 4x channels and thought that this will take no time at all.
The PSU is ok but fuses are blowing when I connect the power amp PCBs.
I thought that there must be a short somewhere and measured resistance between the positive and negative rail on the PCBs (PSU disconnected) and found it to be just above 1R.
So, does anyone remember these old amps?
I have attached the schematic which should be mostly correct anyway.
Hopefully someone can assist me with some troubleshooting, I kind of realized that I should do something I actually can learn instead but I want to finish this 🙂
I planned on getting out of this hobby, mostly due to lack of time for building and learning.
So, I thought "why not make a pre amp and a simple power amp and leave it at that?".
I decade or two ago I build Greg Balls GB150 and for some reason I sold it.
I managed to find old kits for 4x channels and thought that this will take no time at all.
The PSU is ok but fuses are blowing when I connect the power amp PCBs.
I thought that there must be a short somewhere and measured resistance between the positive and negative rail on the PCBs (PSU disconnected) and found it to be just above 1R.
So, does anyone remember these old amps?
I have attached the schematic which should be mostly correct anyway.
Hopefully someone can assist me with some troubleshooting, I kind of realized that I should do something I actually can learn instead but I want to finish this 🙂
Check resistance between each rail and the output terminal to isolate the short to one half.
Check D1 and D2 separately. Check Q 11-14 each separately.
The metal backs of Q11-14 could be shorting to the heat sink.
Check D1 and D2 separately. Check Q 11-14 each separately.
The metal backs of Q11-14 could be shorting to the heat sink.
Resistance between either rail and positive speaker output is 6R5
Between either rail and negative output (ground) is 1R8.
They have no metal back, they are all plastic.
How do I check them, do I need to desolder them?
One thing.
Resistance between the middle leg of Q12 and either positive rail, negative rail or ground all gives around 2R.
Resistance between the middle leg of Q12 and either positive rail, negative rail or ground all gives around 2R.
First check the diodes in circuit with the red meter lead on the anode, using the diode function.
You should get a beep, or a few hundred ohms, depending on your meter.
Make sure they were installed with the correct orientation, banded end towards the more positive voltage (up).
If any doubt, remove them and check again. While they are out, recheck the Q11-14 in circuit again.
You should get a beep, or a few hundred ohms, depending on your meter.
Make sure they were installed with the correct orientation, banded end towards the more positive voltage (up).
If any doubt, remove them and check again. While they are out, recheck the Q11-14 in circuit again.
Ok then check the Q11-14 out of circuit.
They must be the problem.
Also check the D3 and D4 Zeners.
They must be the problem.
Also check the D3 and D4 Zeners.
Crap, I might know what it is. I need an hour or so to put the kids to bed.
But, say that I put a 5W 0R15 (0.15R) instead of D1 and D2.
What would the consequences of that be?
Yes, they would be essentially bypassed by the resistors.
Of course, the transistors could already be bad.
Of course, the transistors could already be bad.
Ok, this is what the moron (me) did.
I got these kits without manual so I looked around and finally found two different versions along with some descriptions of mods later implemented online and not in these manuals.
One mod present was to add a resistor in series with each rail to reduce ripple, I managed either to read wrong or mix up different versions on the boards.
Anyhow, I managed to put these resistors instead of D1 and D2.
I just removed them and tried to start it up.
Now to the next thing, I only have 2A fuses and of course they blow. The transformer is rated somewhere around 300VA, possibly a bit higher, possibly lower.
So I can't tell if it is to small for a toroid but I will get 3A slow blow asap.
A variac is an even more effective friend. 🙂
No, that wasn't it.
I put a 3.15A slow-blow in and after a few second something cracked and the fuse blew.
I think I'll just order an icepower module and leave it at that and put the stuff for this amp in a box for a rainy day
I put a 3.15A slow-blow in and after a few second something cracked and the fuse blew.
I think I'll just order an icepower module and leave it at that and put the stuff for this amp in a box for a rainy day
Did you hit it with full power? If so, I would expect something like that.
If you didn't soft start it, you may have extended the damage. You can use a variable bipolar DC power supply and run it at lower voltage to troubleshoot. You'll find the variac or DC power supply far more effective in helping you fix it without losing more parts.
If you didn't soft start it, you may have extended the damage. You can use a variable bipolar DC power supply and run it at lower voltage to troubleshoot. You'll find the variac or DC power supply far more effective in helping you fix it without losing more parts.