Problem found:
I checked and compared each resistor on the board between channels and found that R35 and R39 (soldered on the board) have about 0.5-0.8Meg instead of 1Meg like in a good channel. I have seen this problem before, unsoldered R35 and R39 have 1Meg, that's why I replaced the OP AMP. Since the board had no suspicious areas, I did not see any problem and looked for leaks in the components.
There is a leakage of about 1-3 Meg on the board between pins 5-6-7-8 of the OP AMP and R35/39, at least.
I removed OP AMP, film capacitor, cleaned the top of the PCB with ethanol, the cotton swab turned dark brown, like after pine resin.
I cleaned and installed all the native parts back, and everything works fine, let's hope.
I noticed that many resistors on the PCB are placed above the board tracks without gaps, so they can short them.
Measurements:
Driver boards with 7 transistors in parallel: 0.64-0.65V at 150 ohms, 4.2mA 67.5Vce 0.28W per transistor - they are quite hot, 2W per board.
MOSFET 0.003V at 0.1R, 30mA per transistor (measured in "Volts" range)
Power consumption at 230VAC:
Start up: 38W (BIAS LEDs on)
Operating mode: 57-58W (BIAS LEDs off, AMP LED on) - in this mode the feedback works and the BIAS control depends on the mains voltage. I use a 150W light bulb for protection, and it flashed very brightly periodically.
If you remove the BIAS boards and the tubes, the driver transistors will generate square pulses at about 1Hz, so you cannot test the amp without the tubes. You need to install BIAS boards, and then you can check without tubes.
Difference in the circuit (Unico SE):
R38a/R80a are shorted instead of 4.7R.
Questions:
1) When amp turned on, a faint "pum" sound is heard from the speakers. Is this normal?
2) 5 seconds after switching on, very quiet music is heard in the speakers. In the operating mode, the sound becomes normal. Does the amplifier really not have 100% mute at startup?
I checked and compared each resistor on the board between channels and found that R35 and R39 (soldered on the board) have about 0.5-0.8Meg instead of 1Meg like in a good channel. I have seen this problem before, unsoldered R35 and R39 have 1Meg, that's why I replaced the OP AMP. Since the board had no suspicious areas, I did not see any problem and looked for leaks in the components.
There is a leakage of about 1-3 Meg on the board between pins 5-6-7-8 of the OP AMP and R35/39, at least.
I removed OP AMP, film capacitor, cleaned the top of the PCB with ethanol, the cotton swab turned dark brown, like after pine resin.
I cleaned and installed all the native parts back, and everything works fine, let's hope.
I noticed that many resistors on the PCB are placed above the board tracks without gaps, so they can short them.
Measurements:
Driver boards with 7 transistors in parallel: 0.64-0.65V at 150 ohms, 4.2mA 67.5Vce 0.28W per transistor - they are quite hot, 2W per board.
MOSFET 0.003V at 0.1R, 30mA per transistor (measured in "Volts" range)
Power consumption at 230VAC:
Start up: 38W (BIAS LEDs on)
Operating mode: 57-58W (BIAS LEDs off, AMP LED on) - in this mode the feedback works and the BIAS control depends on the mains voltage. I use a 150W light bulb for protection, and it flashed very brightly periodically.
If you remove the BIAS boards and the tubes, the driver transistors will generate square pulses at about 1Hz, so you cannot test the amp without the tubes. You need to install BIAS boards, and then you can check without tubes.
Difference in the circuit (Unico SE):
R38a/R80a are shorted instead of 4.7R.
Questions:
1) When amp turned on, a faint "pum" sound is heard from the speakers. Is this normal?
2) 5 seconds after switching on, very quiet music is heard in the speakers. In the operating mode, the sound becomes normal. Does the amplifier really not have 100% mute at startup?
Congratulations to a successful repair.
This amp does not have a speaker relay. Some slight noise at switch on is normal.
Do not worry about the switch on mute, it is ok.
This amp does not have a speaker relay. Some slight noise at switch on is normal.
Do not worry about the switch on mute, it is ok.
Hi all,
I have an unico 90 amplifier where the right channel is 3db quieter than the left channel.
Swapping the tubes crosswise has not been successful. Has somebody a service manual or a schematic for me?
Thanks in advance
Emil
I have an unico 90 amplifier where the right channel is 3db quieter than the left channel.
Swapping the tubes crosswise has not been successful. Has somebody a service manual or a schematic for me?
Thanks in advance
Emil
Thanks for uploading the Unico P service manual, it is really helpful! I’m just starting a repair now and opened it up to find multiple blown fuses, so the hunt for issues begins after checking them. 🙂
I have similar problem with my Unico (2x80w). A local HiFi specialist using oscilloscope found the problem. In my case The 2db difference between Left-Right is caused by the volume potentiometer. Unison Research is using Alps motorized potentiometer made in Japan. It's very easy to find it in Europe and costs 30 Euros. I will also do a full Recap. The technician is trying to find the original Itelcond capacitors. These are Industrial grade capacitors and very hard to find them outside Italy. A great alternative probably is Mundorf. I will also replace the 2xECC82 Tubes. After all these my 15 years old Unico will be new again. I am waiting all the parts to arrive and I will share with you the results.
outlawviper:
I am currently experiencing the following phenomenon. Most of the time both channels are the same, but after a few days the left channel is 3dB louder again. This changes back and forth. The Alps potentiometer could possibly be to blame. I will also change ECC82.
I am currently experiencing the following phenomenon. Most of the time both channels are the same, but after a few days the left channel is 3dB louder again. This changes back and forth. The Alps potentiometer could possibly be to blame. I will also change ECC82.
Hi all!
I bought a UR Secondo in dire conditions, one of it´s output capacitors got literally burned, leaving a huge hole on the main board. Most of the damage has already been fixed but there are 2 small resistors on the pre amp section whose trails got burned as well. Unfortunately, I wasn´t able to track the resistor path down and the diagram provided on this topic doesn´t present enough information for me to do so.
Does anybody here could please help me out providing a high res picture of the board or a in depth schematics so I can try to bring this beauty back to life?
Thanks in advance!
Here are some beofre/after pics:
I bought a UR Secondo in dire conditions, one of it´s output capacitors got literally burned, leaving a huge hole on the main board. Most of the damage has already been fixed but there are 2 small resistors on the pre amp section whose trails got burned as well. Unfortunately, I wasn´t able to track the resistor path down and the diagram provided on this topic doesn´t present enough information for me to do so.
Does anybody here could please help me out providing a high res picture of the board or a in depth schematics so I can try to bring this beauty back to life?
Thanks in advance!
Here are some beofre/after pics:
Hi All ,
Recently my Unico CDP has got problem somehow! In order to troubleshoot the CD player myself, I'm hoping to get a service manual or schematic diagram.
Before posting this request, I searched the forums extensively using terms like "Unico CDP schematic," "Unico CD service manual," and variations of the model name. Unfortunately, I haven't been able to find the specific documentation I need.
Would anyone in the community happen to have access to, or know where I might find, the schematic diagram or service manual for the Unico CDP CD player ?
Any pointers, suggestions, or shared knowledge would be immensely appreciated.
Thanks a lot in advance.
James
Recently my Unico CDP has got problem somehow! In order to troubleshoot the CD player myself, I'm hoping to get a service manual or schematic diagram.
Before posting this request, I searched the forums extensively using terms like "Unico CDP schematic," "Unico CD service manual," and variations of the model name. Unfortunately, I haven't been able to find the specific documentation I need.
Would anyone in the community happen to have access to, or know where I might find, the schematic diagram or service manual for the Unico CDP CD player ?
Any pointers, suggestions, or shared knowledge would be immensely appreciated.
Thanks a lot in advance.
James
Attachments
Hi as_audio, nice to know you, and thanks for your response.
The Unico CDP player powers on, and the display shows the valve countdown as expected.
However, after playing for a short while, it experiences audio dropouts intermittently or sometime completely, even though the transport appears to be functioning. The signal cuts off unpredictably, affecting the analog output in my current setup.
This issue does not resolve on its own—a full power cycle and cooldown period are required for recovery.
I have tried multiple discs and swapped the signal cables and connections, but the issue persists.
The transport remains responsive, and no playback errors or unusual noises occur before the failure.
Let me know if you need any additional information.
Thanks and best regards,
James
The Unico CDP player powers on, and the display shows the valve countdown as expected.
However, after playing for a short while, it experiences audio dropouts intermittently or sometime completely, even though the transport appears to be functioning. The signal cuts off unpredictably, affecting the analog output in my current setup.
This issue does not resolve on its own—a full power cycle and cooldown period are required for recovery.
I have tried multiple discs and swapped the signal cables and connections, but the issue persists.
The transport remains responsive, and no playback errors or unusual noises occur before the failure.
Let me know if you need any additional information.
Thanks and best regards,
James
Yes, that's correct—most of the time, both channels drop out simultaneously. On rare occasions, it may affect only one channel, with the right channel being slightly more prone than the left, though this happens infrequently.
So it doesn’t appear to be channel-specific, which, as you suggested, points to a potential issue in the output stage or its associated power supply.
Thanks again for your valuable insight—I truly appreciate your time and support!
So it doesn’t appear to be channel-specific, which, as you suggested, points to a potential issue in the output stage or its associated power supply.
Thanks again for your valuable insight—I truly appreciate your time and support!
So what kind of tools and instruments do you own and has this item been worked on before ?
In this forum people are expected to provide complete and precise informations.
In this forum people are expected to provide complete and precise informations.
Thank you for your insightful response.
I have several basic tools and instruments, including multimeters, oscilloscopes, a signal generator, as well as a soldering iron and desoldering tools.
The Unico CDP remains in its original condition. My only intervention was a previous attempt to replace the valve with a GE 5654 as a substitution, with no other modifications or servicing performed.
At the moment, I am gathering more relevant information, such as a service manual or schematic etc... Once I get ready, I plan to conduct measurements and troubleshooting, possibly over the weekend.
Your advice is greatly appreciated!
I have several basic tools and instruments, including multimeters, oscilloscopes, a signal generator, as well as a soldering iron and desoldering tools.
The Unico CDP remains in its original condition. My only intervention was a previous attempt to replace the valve with a GE 5654 as a substitution, with no other modifications or servicing performed.
At the moment, I am gathering more relevant information, such as a service manual or schematic etc... Once I get ready, I plan to conduct measurements and troubleshooting, possibly over the weekend.
Your advice is greatly appreciated!
Check the various supplies, 6,3V for filaments, 5V, 12V, and 150V for tube.
All are made with LM317 or the like (not stated which one for 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.
All are made with LM317 or the like (not stated which one for 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.
I sincerely appreciate your valuable suggestions.
I'm still searching for the service documentation or schematic, as having it on hand would be helpful aid in identifying and tracing the test points and measurement parameters.
while continue searching, I'll focus on identifying the relevant test point locations based on your recommendations and will share my findings, likely by the weekend.
Your expertise has given me a strong foundation to move forward.
Many thanks again!
I'm still searching for the service documentation or schematic, as having it on hand would be helpful aid in identifying and tracing the test points and measurement parameters.
while continue searching, I'll focus on identifying the relevant test point locations based on your recommendations and will share my findings, likely by the weekend.
Your expertise has given me a strong foundation to move forward.
Many thanks again!
Hi as_audio,
Following your guidance, I measured the following voltages:
-at Transport power points: Stable +5V and +12V
- at ECC82 plate voltages:
~71V (with valve),
~82V (without valve)
***No voltage changes observed during audio dropout events
However, thermal imaging revealed several blue resistors operating at 127–134°C (see attached photo). Even with the chassis open, these temperatures seem excessive.
Key questions:
1. Are these temperatures exceeding safe operating limits? (If assuming rated 155°C, they're near maximum and may degrade prematurely)
2. Could this overheating be the root cause of the issues?
3. What specific voltage/current measurements should I check next? (Particularly at these hot components)
Your expert advice would be invaluable. Many thanks for your continued help!
Following your guidance, I measured the following voltages:
-at Transport power points: Stable +5V and +12V
- at ECC82 plate voltages:
~71V (with valve),
~82V (without valve)
***No voltage changes observed during audio dropout events
However, thermal imaging revealed several blue resistors operating at 127–134°C (see attached photo). Even with the chassis open, these temperatures seem excessive.
Key questions:
1. Are these temperatures exceeding safe operating limits? (If assuming rated 155°C, they're near maximum and may degrade prematurely)
2. Could this overheating be the root cause of the issues?
3. What specific voltage/current measurements should I check next? (Particularly at these hot components)
Your expert advice would be invaluable. Many thanks for your continued help!
