Most probably it is not RFI only. The amplitude is too high, voltage swing about 70mVp-p, ripples with approx. 5MHz repetitive frequency. What happens if you turn off the mains power for the power supply? Do the oscillations disappear?
If the signal is also visible on GND then there is something in the environment that induces this signal in the connection leads of the scope.
You need to check the scope connections and the mains connections.
If there is an HF oscillation, the ground may become easily contaminated as well. He has too switch of the power with everything else connected same. He also should seek for equipment with switched mode power supplies connected to the same AC line. Anyway, the plot he posted is to regular to be a product of SMPS, these products usually measure as bursts of high frequency damped impulses with some lower repetition frequency. And he complains for hot transistors.
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Thank you for your answer, so this high voltage will come down after a while.
I will check again after some time.
The 2,2 V across the ext. RIAA is no problem also? Both boards.
My 0,0000 V at the input looks strange, as I said the trimmer has no function to the input. Both boards.
Should I change the trimmers?
Regards,
Christoph
Can you give me the voltages at TP101,102,103 and 104 and also TP201,202,203 and 204.
Running the shunts from 37V is a bit much, try to run them from 30V or slightly less.
Remove C105 and C205 and see if the oscillations/noise are/is gone.
Thank you for your help so far...
37V into shunt, amp not connected.
TP201 -18.07
TP202 -19.45
TP203 -22.06
TP204 -0.533
TP101 18.06
TP102 19.66
TP103 22.16
TP104 0.552
I don't have a Traffo 18V handy. The next one down I have is only 15v, which isn't enough. I did try the 15V one but half the LEDs under the heatsink didn't illuminate correctly.
At 37V in the heatsink does get a little toasty
I've only run the board for periods of about 15mins so far.
Okay, not tried this yet.
37V into shunt, amp not connected.
TP201 -18.07
TP202 -19.45
TP203 -22.06
TP204 -0.533
TP101 18.06
TP102 19.66
TP103 22.16
TP104 0.552
I don't have a Traffo 18V handy. The next one down I have is only 15v, which isn't enough. I did try the 15V one but half the LEDs under the heatsink didn't illuminate correctly.
At 37V in the heatsink does get a little toasty
I've only run the board for periods of about 15mins so far.Okay, not tried this yet.
I let some magic smoke out today.
The two bottom LED's on the left hand edge of the board burnt out along with the 337 that you can see with its die exposed.
Was this likely caused by a failure in one of these 3 components or is it more likely a failure or a short on one of the components on the heatsink?
An externally hosted image should be here but it was not working when we last tested it.
The two bottom LED's on the left hand edge of the board burnt out along with the 337 that you can see with its die exposed.
Was this likely caused by a failure in one of these 3 components or is it more likely a failure or a short on one of the components on the heatsink?
Under normal operating conditions the 337 will carry 2mA's of current, that will be 2mA * 24V (if the supply is 42V) = 48mW (about/max). The only reason for this failure is a broken power transistor (the output voltage is 18V so the shunt was operating as expected). You should replace Q101, Q102, Q103 and Q104 (I'm almost sure that Q101 or Q103 is broken). Check for shorts between Q101, Q103 and the heatsink (that could be the source of the damaged transistors).
Thanks Guys, Joachim, it wasn't that, it popped within a second of switch on.
FDW, I shall have to draw out parts numbered overlay for the board. I can't follow the schematic in my head like that. I did think it was likely to be a short between the heatsink and the first D45H11 on the very left hand side, there's the faintest indication of arcing on its back.
I'll replace the parts and switch on without the heatsink fitted to check and then go from there replacing the power transistors from left to right if required.
FDW, I shall have to draw out parts numbered overlay for the board. I can't follow the schematic in my head like that. I did think it was likely to be a short between the heatsink and the first D45H11 on the very left hand side, there's the faintest indication of arcing on its back.
I'll replace the parts and switch on without the heatsink fitted to check and then go from there replacing the power transistors from left to right if required.
Listen carefully "DO NOT SWITCH ON WITH NO HEATSINK"
it will destroy the shunt almost instantly! I shall say this only once - YouTube
Yep, I did...
TP201 -19.45
TP202 -18.07
TP203 -22.06
TP204 -0.533
TP101 19.66
TP102 18.06
TP103 22.16
TP104 0.552
That's more like it
O.k. these seem fine. Now try to lower the input voltage (add some series resistance to the transformer output (22ohm will drop (about) 8V (both channels running, else use 50ohm)). Do the scope measurement with and without the capacitors (as earlier mentioned).
FDW, i removed the two D45H11 the one on the left was bust, the one closer to the centre was fine (though trashed for re-use). I replaced both of them with new and also the 337 that had popped.
Now all the LED's around the back of the heatsink light up but the bank on the left hand side don't. I'm guessing the 2nd 337 under the heatsink was fine, as its LED didn't pop- and the 2nd D45H11 was also ok- is that a safe assumption?
If so what next, replace the PMOS?
Now all the LED's around the back of the heatsink light up but the bank on the left hand side don't. I'm guessing the 2nd 337 under the heatsink was fine, as its LED didn't pop- and the 2nd D45H11 was also ok- is that a safe assumption?
If so what next, replace the PMOS?
First give me the test-point voltages and the input voltages (as measured on the board). It also is (may be) smart to replace bort 337's.
Its done , the paradise runs , every light shines , the input offset is adjusted by 0V .
The output offset fluctuated at 30mV , frequenz of fluctuation is around 2Hz so my DMM says ( its a Uni-T 61E ) , whit a dummyload of 220 Ohm ( because my Colibri wants to see this load ).
I will let it burn in for a few days and look at the offset again .
After that i´ll listen and report.
One question , why a opa 134( use for audio) and not a special regulator opa ?
The output offset fluctuated at 30mV , frequenz of fluctuation is around 2Hz so my DMM says ( its a Uni-T 61E ) , whit a dummyload of 220 Ohm ( because my Colibri wants to see this load ).
I will let it burn in for a few days and look at the offset again .
After that i´ll listen and report.
One question , why a opa 134( use for audio) and not a special regulator opa ?
You guys make me crazy with this need to wait several days for the DC to settle. Whatever it is, a capacitor or anything else that is just at the edge of functionality - it is WRONG.
Regarding OPA134 - it is not bad for servo, for the reason of very low input bias currents and acceptable noise.