Au D11ii Transformer Question

[ecommers]

Hey Guys
I'm working on a unit I picked up on e-bay awhile back. All transformer leads are with-in specs except for orange(79), Grey (80), and orange (81). Schematic shows 20 0 20 volts at those pins. The measurements are AC Orange-79 10volts, Grey-80 4.5 volts and orange-81 20 volts ( 10 4.5 20). Measurements were made with the plug connected and disconnected. I tried both spare transformers I have on hand and they also measured about the same voltages.
I then serviced the F4292 board I replaced one bad resistor (R22) and get the same results. Could it be some where else ? F- 4287 perhaps. I can't believe all three transformers are fried the same way.

 

[ConradH]

I assume grey is ground? Lacking connection to ground? I'd measure directly on the leads (or in connectors?) from orange to grey and other orange to grey, then from orange to orange. With the secondary disconnected, measure the resistance from each orange to grey. That should clear things up quickly.

 

[ecommers]

I am measuring the plug straight off the transformer

 

[Hyperion]

I am measuring the plug straight off the transformer

The readings you are getting are so strange, and with 2 transformers! - I have to question just how you are measuring these voltages. Your meter is set to read AC Volts? But where are your meter probes when you are making these measurements? - seems like you have one probe on 79, 80 or 81 - but where are you putting the other probe?

If I was doing this I would be putting one probe on 80, and the other probe on 79 or 81, or one probe on 79 and the other on 81.

 

[ecommers]

I am probing into the socket it self and black is grounded to chassis the meter is set to AC. When I do as your suggestion black on 80 I get 18.7 volts on either side. That's on the transformer that came with the unit, one spare, and one from a working AU D11ii. So three different transformers. It seem to be sending voltage back through the units ground some how, I can not adjust any of the trimmers as they all have about 6 mV read out There is no adjustment when you turn the trimmers either way. (that would be the EQ and tone control board trimmers only).
I'm thinking something on F-4287 is feeding this voltage back. Diode ? Transistor ?
I was hoping some else had encountered this in the past and had a little knowledge to pass on.
I just trying to same my self from all the fun of tearing down the amp on that side for now.

 

[Hyperion]

But where are your meter probes when you are making these measurements? - seems like you have one probe on 79, 80 or 81 - but where are you putting the other probe?

If I was doing this I would be putting one probe on 80, and the other probe on 79 or 81, or one probe on 79 and the other on 81.

I repeat - this is important - please answer these questions.

OR alternatively what DC Voltage are you seeing as output from F-4292 pins 82 and 83 (should be ~ -21V) And also from F-4292 pins 83 and 84 ? (should be ~21V)

You seem to have worked your way back from a perceived fault with the amplifier, but may have got yourself confused about the AC readings from the transformer (as I can't believe 3 transformers are faulty - or any in fact)

 

[ecommers]

I repeat - this is important - please answer these questions.

OR alternatively what DC Voltage are you seeing as output from F-4292 pins 82 and 83 (should be ~21V) And also from F-4292 pins 83 and 84 ? (should be ~21V)

You seem to have worked your way back from a perceived fault with the amplifier, but may have got yourself confused about the AC readings from the transformer (as I can't believe 3 transformers are faulty - or any in fact)

82 reads 0.62 vDC and 83 reads 0.00vDc Meter set to DC I get
0.267 pin 79 and 0.644 on pin 81.

 

[Hyperion]

Well, that regulator is clearly not working, which brings us back to those AC voltage measurements as a first step in finding out what is wrong there.

Can you set your meter to 'AC Volts' place one probe on F-4292, pin 80 and use the other probe to measure the voltage at pins 79 and 81 - please note the voltages and report back.

These measurements can be with the transformer connected to the F-4292 board, but if you get anything other than the correct readings, unplug the connector from the board and measure directly out of the transformer - both probes measuring on the connector at pin 80, and pin 79 & 80.

 

[ecommers]

I believe I found part of the problem the fluke 87 I was using was giving me the readings I posted in the beginning of the thread. with my other meter this is what I'm getting Orange Grey Orange Plug disconnected from F-4292 measuring at the plug socket directly coming from the transformer. Meter set on AC, Black lead to 80. Ac voltage at 79 is 18.75 and 81 is18.74.
Measurements off the plug from control board F-4273 that goes to selector board 4271 reads, 82 @ + 327mV DC, 83 @ 0.00, and 84 @ - 223mV DC.

 

[Hyperion]

Oh well that's a relief - the transformer is OK - But... the regulator seems to be 'zorched'

What happens when you put one probe in 83 and the other probe in 82 or 84 ? - in other words do not use (another) ground as a reference - as is suggested by the 0.00 reading at 83.

 

[ecommers]

Any modern replacement ?



I get 82 @ + 356mV DC and 84 @ - 176mV Dc.

 

[Hyperion]

Any modern replacement ?

You'll need to check mR21 & mR22 (resistors) and the voltage coming from the bridge rectifier. If all OK the problem could be mQ21 & mQ22 transistors - but really needs to be carefully checked as any of the semiconductors in that circuit could have faults that will prevent proper regulated output - and could damage new components if this is not diagnosed accurately. I am assuming nobody has changed any components already, especially mC31 & mC32 - and put them in back to front, as this will have the effect you are seeing.

There are modern equivalents - but we need to know what component(s) are at fault.

 

[ecommers]

I did this work prior, recapped board replaced diodes 21 & 22 with a pair of 22 V 1/2 watt zener's ( TZX22C-TR), check all the resistors Replaced R21 & 22. *(R22 was bad). Check C21 & 22 ok.
All transistors & rectifiers checked OK with an Atlas DCA75

 

[ecommers]

I found the problem. All three pins 79, 80, and 81 had been pushed so hard that they gave way from the foil on the back and were not making contact with the board.
Now I'm getting the correct readings. This amp has been fighting me all the way. I will win the battle.
Thanks Hyperion for all your help.

 

[ecommers]

With that mystery solved I found both ub-152's were bad. Lucky I had two from a parts unit. Control board voltages are now all correct.
Q1 on the EQ board is getting 17 volts at the collector so I've got some work to do there.

 

[SoundOfSound]

I believe I found part of the problem the fluke 87 I was using was giving me the readings I posted in the beginning of the thread. with my other meter this is what I'm getting Orange Grey Orange Plug disconnected from F-4292 measuring at the plug socket directly coming from the transformer. Meter set on AC, Black lead to 80. Ac voltage at 79 is 18.75 and 81 is18.74.
Measurements off the plug from control board F-4273 that goes to selector board 4271 reads, 82 @ + 327mV DC, 83 @ 0.00, and 84 @ - 223mV DC.

The Fluke 87 is a great volt meter. I noticed that they start acting a little funny when the battery goes down too low. Just replace the battery with an approved one and it should start acting normal again.

https://www.manualslib.com/manual/451847/Fluke-87v-Ex.html?page=47#manual

It's a total PIA to replace it but if you remove the three screws on the back and wiggle the plastic cover just right you can get into it.

 

[ecommers]

You are correct about the battery. The reason I didn't think of that was I just replaced it a month ago. Must of been a week from the start.