by the way, the Filament supply: Measured 6.2V (presumably for parallel wiring) / 12.6V (series)
Again , No voltage fluctuations during audio dropouts
Again , No voltage fluctuations during audio dropouts
There seems to be a lot of dust in the player. If you have access to an air compressor try to remove the dust. Check solder joints of these resistors. Which designation do they have ?
Plate voltage at regulator output is nominal 150V.
"Muting transistors are T6 and T8, they receive a common signal at their bases via R79 and R93 which are common to the mute line. You may want to check the voltage at this point when the signal drops out". This way we can see it is the muting function or some other form of drop out.
Plate voltage at regulator output is nominal 150V.
"Muting transistors are T6 and T8, they receive a common signal at their bases via R79 and R93 which are common to the mute line. You may want to check the voltage at this point when the signal drops out". This way we can see it is the muting function or some other form of drop out.
Hi as_audio,
Thank you for your continued guidance. Here's just a quick update:
1. Identified Overheating Components:
Resistors R6, R7, R8, R69, R73, R75, and R87 are operating at 127-134°C(designation photo attached. )
2. Next Steps (as suggested):
- Investigation of Low Plate Voltage:
- Identify 150V plate regulator components ?
- Determine the cause of low plate voltage ?
Your expertise has been invaluable in narrowing down the potential issues. I'll proceed with the measurements and share my findings once completed.
Best regards,
James
Thank you for your continued guidance. Here's just a quick update:
1. Identified Overheating Components:
Resistors R6, R7, R8, R69, R73, R75, and R87 are operating at 127-134°C(designation photo attached. )
2. Next Steps (as suggested):
- Remove dust
- Inspect solder joints on those resistors
- Measure muting circuit (T6/T8 bases via R79/R93) during dropout events
- Investigation of Low Plate Voltage:
- Identify 150V plate regulator components ?
- Determine the cause of low plate voltage ?
Your expertise has been invaluable in narrowing down the potential issues. I'll proceed with the measurements and share my findings once completed.
Best regards,
James
Attachments
R6, R7, R8 are 120 Ohm 1W resistors feeding 5V DAC from the filament supply (12,6V, not 6,3V as suggested in post 138).
You can expect some heat here. Check 12,6V on one side and 5V on the other.
R73 and R87 4k7 3W are voltage droppers in the hv supply line. Check 150V plate supply on one side.
R69 and R75 4k7 3W are load resistors for output emitter followers. Some heat is to be expected on all four.
...
Re the muting circuit it would be good to know these voltages are correlated to the drop out or not.
You can expect some heat here. Check 12,6V on one side and 5V on the other.
R73 and R87 4k7 3W are voltage droppers in the hv supply line. Check 150V plate supply on one side.
R69 and R75 4k7 3W are load resistors for output emitter followers. Some heat is to be expected on all four.
...
Re the muting circuit it would be good to know these voltages are correlated to the drop out or not.
Hi as_audio,
I truly appreciate your invaluable support. Here’s a summary of the key findings based on your guidance:
1. Muting Circuit Behavior During Dropouts:
- R79/R93 input junction remains low
- T6/T8 bases stable at 0.42V
2. HV Supply Status (R73/R87):
- Input: ~159V
- Output: ~88V
3. Output Emitter Follower Load Resistors (R75/R69 - 4k7 3W):
- Follower side: 71.1V / 70.4V
- Assumed ground side: 0V
4. **Critical Discovery:
- R8 (120Ω 1W) was found with an entirely unsoldered pin—only touching the pad somehow !
- Could this be the cause of intermittent dropouts?
Next Steps:
Additionally, I may take preventive measures as some HiFi enthusiasts do:
- Upgrade aging capacitors (likely over 20 years old already) with low-ESR brands (e.g., Rubycon 105°C-rated or similar), particularly in areas near overheated resistors.
Your expertise has been instrumental in pinpointing this issue efficiently.
Many thanks again!
Best regards,
James
I truly appreciate your invaluable support. Here’s a summary of the key findings based on your guidance:
1. Muting Circuit Behavior During Dropouts:
- R79/R93 input junction remains low
- T6/T8 bases stable at 0.42V
2. HV Supply Status (R73/R87):
- Input: ~159V
- Output: ~88V
3. Output Emitter Follower Load Resistors (R75/R69 - 4k7 3W):
- Follower side: 71.1V / 70.4V
- Assumed ground side: 0V
4. **Critical Discovery:
- R8 (120Ω 1W) was found with an entirely unsoldered pin—only touching the pad somehow !
- Could this be the cause of intermittent dropouts?
Next Steps:
- Reflow solder joints on the those resistors, replacing R8 if compromised.
- Upgrade overheated resistors (127–134°C) to higher-power-rated equivalents.
Additionally, I may take preventive measures as some HiFi enthusiasts do:
- Upgrade aging capacitors (likely over 20 years old already) with low-ESR brands (e.g., Rubycon 105°C-rated or similar), particularly in areas near overheated resistors.
Your expertise has been instrumental in pinpointing this issue efficiently.
Many thanks again!
Best regards,
James
These are useful measurements. Voltages seem to be fine. Check R6, R7, R8 in parallel are 40 Ohm.
If you are sure muting voltage remains low all the time (except during warm up I suppose) the reason for drop out must be a different one.
Using a scope check all regulator outputs for oscillation, avoiding shorts.
I do not advise to change caps at random, also to avoid the risk of damaging through hole connections.
If you are sure muting voltage remains low all the time (except during warm up I suppose) the reason for drop out must be a different one.
Using a scope check all regulator outputs for oscillation, avoiding shorts.
I do not advise to change caps at random, also to avoid the risk of damaging through hole connections.
Hi as_audio,
Good day to you, and thank you for your prompt and insightful feedback. Here’s a quick update for discussion:
1) R6, R7, and R8 are measuring between 40R and 60R intermittently, depending on whether R8 maintains proper contact with the pad.
2) The current capacitors are rated at 85°C and have been in use for **over 20 years.
- Given those are close proximity to overheating resistors (127°C–134°C), thermal stress may be impacting their function and accelerating degradation, which I suspect over time could lead to intermittent failures .
I appreciate your caution regarding unnecessary capacitor changes. I’ll take extra care to avoid damaging through-holes during the upgrade.
I’ll also perform scoping on regulator outputs to check for oscillation when time allows, though intermittent issues may take time to be observed.
Thanks again for your expert advice again.
Best regards,
James
Good day to you, and thank you for your prompt and insightful feedback. Here’s a quick update for discussion:
1) R6, R7, and R8 are measuring between 40R and 60R intermittently, depending on whether R8 maintains proper contact with the pad.
- At 134°C, I suspect thermal expansion may be causing R8 to intermittently disconnect from the pad.
- As you mentioned, under normal conditions, 12.6V feeds through R6, R7, and R8 to supply the 5V DAC.
- However, if R8 intermittently loses contact due to overheating, the voltage drop could fluctuate unpredictably, potentially resulting in a lower-than-expected voltage.
2) The current capacitors are rated at 85°C and have been in use for **over 20 years.
- Given those are close proximity to overheating resistors (127°C–134°C), thermal stress may be impacting their function and accelerating degradation, which I suspect over time could lead to intermittent failures .
I appreciate your caution regarding unnecessary capacitor changes. I’ll take extra care to avoid damaging through-holes during the upgrade.
I’ll also perform scoping on regulator outputs to check for oscillation when time allows, though intermittent issues may take time to be observed.
Thanks again for your expert advice again.
Best regards,
James