Traynor Beta 800 testing

[JP-Stereo]

Q1 base was pulsing fast at 3.98vdc before R8 & R9 beging to overheat.
The positive rail was fine but the negative look to have a hard time to raise and was around 35v when i shot it off.
So the shotdown ballancer appear to work by trying to load the positive side via R8 & R9.

Before testing the whole thing with a variac, i wanna try something;
Why not remove the voltage multiplier and the shotdown voltage ballancer to leave only the linear component for the +/- 65 volts rails.
This should make simple basic operational test.


I removed all the components in the red boxes.
Then i end up with a +75vdc / -78 vdc...

Only the transformer give me 48.3vac / ct / 48.3vac and 96vac end to end.
If i add the bridge i have +70vdc / CT / -70vdc and 140vdc +to- with 0.02vac.

So +75vdc / -78vdc from the basic bridge/filter circuit, what can cause this imballance and is it of any significance ?
If so, it should be corrected at this level, before implementing the ballance of the circuits ?

[x-pro]

In your device, the low voltage is the main power supply for the output amplifier. And the supply through the capacitors is for other parts. And it is not stable relative to the common. It mainly depends on the main supply and synchronously with it changes by the value of stabilizer ZD1(ZD2). This source must necessarily be loaded.
When repairing amplifiers, I am not in favor of using a variac on the transformer input, so as not to disturb the real voltage values. If you need to limit the secondary circuit currents, it is better to use tubes at the break of the secondary supply rails. Yes, this will require several lamps, but their wattage can be lower. In addition, such a connection better conveys the current information in the circuit nodes.
As for the parts in the red rectangles. Instead of unsoldering C 1, C2, C3, C4, you can unsolder R1 and R3. The same with the elements to the right of Q1 Q2. It is enough to remove R10, R11.

(Part of the post was deleted due to incorrect translation of the meaning.)

[x-pro]

Q1 base was pulsing fast at 3.98vdc before R8 & R9 beging to overheat.

Check 1N750A (4.7V) in the base of this transistor. Capacitors C1, C2, C3,C4 are the main capacitors for the auxiliary power supply. Their quality should be good.

[x-pro]

So +75vdc / -78vdc from the basic bridge/filter circuit, what can cause this imballance and is it of any significance ?

If the load is disconnected from the source, we can try to explain the imbalance by the presence of a load on the positive bus - the Clip signal display circuit. There is no load on the negative bus. In later versions, a 5 W 2.7 k resistor is used for this purpose.

[JP-Stereo]

No 1N750A diode in this old version.
Same thing for the 2.7k resistor.
I may be logic to add these improvements.

4 components instead of 15 to remove, once more i did not take the shortest path...

The CLIP circuit is currently disconnected so the imballance come from elsewhere...
In order to load the +/-65vcd rail is a standard 60w bulb each side will do or i need DC bulbs
And for the +/-80vdc rail how to evaluate a suitable small load

[x-pro]

oups

What? It's all blown up? Did the device give up its spirit?

[JP-Stereo]

When i received this unit it was toasted.
The power supply had vaporized traces and both amps had defective transistors, diodes and caps.

I removed and tested all the component, replacing what's defective.
I am trying to get the power supply steady first, then i will proceed with one amp at a time.

Any idea for the loads to simulate the amp board running low ?

The 65v rails are the main power, but the voltage doublers are capped by a zenner.
This zenner seem to convert exess voltage in current for the 65v rails.
Otherwise it will produce 130v...

I think we have to load both 65v and 80v rails, but how ?

[x-pro]

The 65v rails are the main power, but the voltage doublers are capped by a zenner.
This zenner seem to convert exess voltage in current for the 65v rails.
Otherwise it will produce 130v..

Zener does not convert redundancy for 65V buses. The 65V supply is several times more powerful than the supply line from C1, C2. The latter will not add anything significant.
Zener ZD1 and resistor R1 is a parametric stabilizer. It is included between the 65V and 80V buses.

[x-pro]

I think we have to load both 65v and 80v rails, but how ?

If all parts of the output stage are intact, the entire amplifier can be connected. Be sure to connect the entire amplifier with no load. Turn on one 60W incandescent bulb at “+65V” and a second bulb at “-65V”. In the event of a short circuit, this bulb at 65V will limit the current in the circuit to 0.92A and will shine brightly. Incandescent lamps have no polarity.

[x-pro]

And for the +/-80vdc rail how to evaluate a suitable small load

For this bus, when connecting the amplifier itself, lamp are not necessary. The current is low. The power supply on R1 and ZD1 can deliver a maximum current of 56 mA.

[x-pro]

So +75vdc / -78vdc from the basic bridge/filter circuit, what can cause this imballance and is it of any significance ?

This difference is determined by capacitors C5-C10 after the bridge. They're not all perfect. Some of them filter better and the voltage is higher there.
For an output stage at 65V supply voltage, this is of little importance.

[JP-Stereo]

I've connected a small load to the +/-65vdc rail to drain the capacitors; 2.2 k ohms 7 watts.
If i leave it there when the PS is power on, nothing seem to overheat and i have +77/-80 vdc.

Without the amp board the CLIP leds are on.

Now i will try with 1 amp board at a time...

[JP-Stereo]

Forget to tell that i also change the ZD3 for a real BZX79.

So in order to safely power up the amp board, at least for the initial test, we insert a 60w bulb in serie with each 65v rail ?

Do i got it right ?

[x-pro]

Do i got it right ?

Yes

[JP-Stereo]

I finally done it !
First, only one amp board in and it is working on the positive side but not on the negative as per the board two leds.
I desolder the predriver transistors for bench testing and also double check each resistors and diodes in the predriver circuit.
Found a leaky transistor on the negative side Q9 and a suspect diode ZD11 then i've replaced them.
Now positive and negative side leds are working and all the test points voltages are right on specs.
But i cannot adjust the bias with VR42, TP1 and TP2 stay steady at 0.190mv, it should reach 0.004v.

The original Q11 was testing defective from the begining and was replaced, but i don't have the test data of the replacement device.
I think i will have to remove this new Q11 in order to confirm it's state as about everything around just have been double checked...

No smoke yet !