Traynor Beta 800 testing

[JP-Stereo]

Hi, i just complete a component check on a Traynor Beta 800 that had burned traces on the power supply board.
I found defective outputs, drivers and predrivers as well as a protection Triac and so, a few diodes too.
Once the overall done, suspect or defective components replaced, i also check the electrolytics and changed a few.

This is a pretty heavy and big amp with 8 big metal case outputs on each channel.

I want to power it up just the power supply first.
What should i expect as a power draw without both power amp boards ?

What is the safest procedure for testing a badly injured amp once repaired ?

I currently have a 200w bulb in serie and it glow dim but steady in a 10 second test, the +65v/-65v look to stabilise.
But i don't wait more for now...

[JP-Stereo]

The power supply is functionnal but the voltages are not in specs.

Before the bridge i have 135vac and 141vac.
After the bridge i have a +67v steady and -95v slowly ramping up...

On the +/-80v bus, i have +80v and -95v clean enough.
and on the +/-65v bus, i have +67v and -92v after about 1 minute after Power On.

Something is weird...

[dmeek]

I have repaired many Beta 800s over the years. Very often I found Q12 or Q13 (MJE340 MJE350) had arced over to the heatsink, burning traces on the pcb. I would replace the steel screws with plastic and make sure the
insulator hole is no bigger than needed. No other damage was caused by this. Don't know if this is related to your problem but it's something to check.

[JP-Stereo]

Nice to know that, i will check.

What do you think of the power supply voltage not being symetrical ?

And that the positive is steady but the negative is slowly ramping up...

I include the best schematic i have for the amp circuit page 1.

[dmeek]

Are you using an oscilloscope? Check for ripple on the main filter caps.

Here is a better schematic

[JP-Stereo]

I also change the four 1N4004 after the bridge, the BZX79 were replaced earlier.

Now the 80v rails are +79, -95 and the 65v rails are at +65.5, -71.5...
No ripple in AC 5v/div.

Only caps and resistors left, unless the transformer is out of specs...

[g1]

This is still with amp boards disconnected?

[JP-Stereo]

Yes, power supply unloaded.
Measurments taken at the empty Power Supply ribon cable connectors to amp.

Maybe disconnecting the TX to Bridge in order to confirm if this unballancing is starting at the TX ?

[JP-Stereo]

Direct on the unplugged secondary of the transformer.
I have from sides to CT ; 48.43vac and 48.44vac, from side to side = 96vac on an RMS multimeter.
Pretty symetrical at this point.

I've found that one wire was sqweezed under the bridge, doesn't look like it was short yet, but it was not ok. (WC10 to WC6) a secondary AC supply.

I will try it with this corrected...

[g1]

It's a bit of an uncommon type power supply. If it is still unbalanced with loads disconnected, you will need to check all the diodes and electrolytic caps in this area:

[JP-Stereo]

Hi, i've removed and tested all the big caps 6800uf, they are pretty much on their specs.
Since the problem is on the negative rail, next i will remove all the diodes there and test them on a loaded test circuit.

All the other caps, the diodes and the regulators have been changed once, except for the bridge...

Looking at D1-D3 and ZD1-ZD2, they are not symetrical...

I have 3 schematics that specified a 1N4004 for D1 and a BZ79 for ZD1, that way i should be symetrical ?

And i can not find anything on BZ78 or 1N5801...

[Helmholtz]

I think "BZX78" is a typo.
There's no reason to use 2 different 16V zeners for ZD1/ZD2.
You should measure 16V across each.

[g1]

I think "BZX78" is a typo.
There's no reason to use 2 different 16V zeners for ZD1/ZD2.

Agree. And I think you will find D1 to be 1N4004. Or else there will be more 1N5801 than just D1 (it is fast recovery).
Look at the schematic from your first post, the parts you noted are all symmetrical, and ZD1 is BZX79.

[JP-Stereo]

Ok you're right, it's symetrical up to Q1 (BD649) and Q2 (BD650).

Q1 is driven by a sampling of the negative rail via ZD5.
Q2 is driven by a sampling of the positive rail via ZD4.
And ZD3 is limiting the difference i think.
Wich one of them is affecting the negative rail ?

I have a new but leaky Q1 (BD649 at C-E 0.5ua)... Q2 is ok.

All the big caps are testing OK.
I've swap C1-C2 for C3-C4, no difference.
All the diode test OK and similar in drop.

I've replace R11 wich show sign of heating.

Still have a stable +65vdc and a moving -80vdc...

[x-pro]

What about the 5W 2.7k resistor in parallel and to the right of C10?
ZD3 maintains symmetry between the plus and minus of the power supply.
In general, it is not recommended to connect a power supply with a parallel stabilizer without a load. This is probably why you have unstable values.