SONY DHR-1000VC - Sound problem

[jonnybravo]

Hello everyone!
I have a SONY DHR-1000VC. When I bought it, it had the following problem: the sound on the RCA or SCART output had a hiss. On the other hand, on the FIREWIRE output, the sound was OK.
I started by checking the electrolytic capacitors.
I found at least 20 out of parameters and decided to replace them.
I replaced all the capacitors, on all the boards, over 140 pieces. The surprise was that almost all the capacitors had started to leak and a large part of them were defective.
After replacing the capacitors, the device works ok but the problem with the sound still exists, that is, there is a hiss on the RCA and SCART output, but on the FIREWIRE output the sound is perfect.
What do you think I should investigate next?
Thanks in advance for your suggestions.

[timtape]

Th RCA and Scart audio outputs are analog. Analog outputs will always have some hiss when operating although it's usually quiet compared to the program and not a problem. But dont expect "digital silence" from analog outputs. It's only a problem if that hiss is audible when playing a tape. Is the hiss the same sound and level on left and right outputs?
Can you upload an audio or video file of the problem?

[jonnybravo]

Th RCA and Scart audio outputs are analog. Analog outputs will always have some hiss when operating although it's usually quiet compared to the program and not a problem. But dont expect "digital silence" from analog outputs. It's only a problem if that hiss is audible when playing a tape. Is the hiss the same sound and level on left and right outputs?
Can you upload an audio or video file of the problem?

Is very audible.
Maybe hiss isn't the right word.
It's really noisy.
I will upload a file.

[videoAI]

Causes of Audio Hiss

1. **Signal Path Components**
- Investigate the analog signal path components between the internal circuit and the RCA/SCART outputs
- Check op-amps and audio amplification stages specific to these outputs
- Compare the circuit design differences between these outputs and the FIREWIRE output

2. **Grounding Issues**
- Examine ground plane connections
- Look for potential ground loop problems
- Verify proper shielding of analog audio circuits

3. **Analog Stage Components**
- Inspect resistors in the audio signal path
- Check for any degraded or out-of-tolerance resistors
- Verify the condition of audio coupling capacitors (even though you've replaced electrolytic caps)

4. **Noise Coupling**
- Investigate potential electromagnetic interference (EMI) sources
- Check cable routing and proximity to power circuits
- Examine the physical layout of audio circuit boards

Recommended Next Steps

1. **Detailed Circuit Tracing**
- Use a multimeter to trace the analog audio signal path
- Compare the circuit design between RCA/SCART and FIREWIRE outputs
- Look for any differences in amplification or signal conditioning stages

2. **Component-Level Inspection**
- Check op-amps (operational amplifiers) in the analog audio path
- Measure resistance and capacitance of components in the signal path
- Look for any signs of thermal stress or previous repairs

3. **Signal Integrity Test**
- Use an oscilloscope to examine the audio signal at different stages
- Compare signal quality between FIREWIRE and analog outputs
- Check for any noise injection points

A key point to consider is that the FIREWIRE output works perfectly, which
suggests the issue is specific to the analog (RCA/SCART) signal path. This
narrows down our investigation to:

1. Analog signal conditioning circuits
2. Output stage amplifiers
3. Potential impedance mismatches

[johnmeyer]

Here's a really dumb idea: check to see if the deck is set to output the linear or the Hi-Fi audio track. If it is set to linear, you will get a LOT of hiss.

Of course, if the only audio on the tape is on the linear track, then this will not help.

[jonnybravo]

This is a clip with the sound problem.
https://files.videohelp.com/u/298536/sound.mp4

[jonnybravo]

This is a clip with the sound problem.

[jonnybravo]

Here's a really dumb idea: check to see if the deck is set to output the linear or the Hi-Fi audio track. If it is set to linear, you will get a LOT of hiss.

Of course, if the only audio on the tape is on the linear track, then this will not help.

I couldn't find a setting related to linear or HiFi audio.