Neotek Elite-
Installed the 2nd to last re-switched stereo channel.
Loftech signal generator in studio B buzzing, even when off.
This is one of those things where the power connects directly to the primary of the power transformer, and the "power" switch closes the connection between the secondary and rectifier. I'm going to shot-gun the power supply and replace the electrolytics, since there aren't that many, and it's 40 years old?
Brian recapped the thing, and it's quiet now.
DI and EApreq500 buidin'
Found out it'll be another 4 months before we get another batch of switches for the DI box. This is exceedingly frustrating! Scouring for NOS.
Re: GReg-Electrical Tech Journal Redux
112Stress testing the Neotek Elite PS4 power supply, recently rebuilt by JSP, using 8 ohm resistors across the ±18v rails (1 each, drawing 2.25A).
Neumann U67
No output.
Tube was dead, replaced.
MANLEY Elop Studio B-
Right channel cutting out intermittently (period of weeks). Signal would pop back on after a sharp signal level peak.
Brian sourced it to one of the 1/4" I/O connectors. The signal goes through them, and their "normal" connections on the way to or from transformers when you're using the XLR connectors. This is like the achilles heel in guitar amps, the effects loop connectors failing the same way. I hard wired the audio across the switching contacts, and labeled the back as much.
Neumann U67
No output.
Tube was dead, replaced.
MANLEY Elop Studio B-
Right channel cutting out intermittently (period of weeks). Signal would pop back on after a sharp signal level peak.
Brian sourced it to one of the 1/4" I/O connectors. The signal goes through them, and their "normal" connections on the way to or from transformers when you're using the XLR connectors. This is like the achilles heel in guitar amps, the effects loop connectors failing the same way. I hard wired the audio across the switching contacts, and labeled the back as much.
Re: GReg-Electrical Tech Journal Redux
113-Elsewhere-
Work on MCI JH24 -
Tape won't play without a little push, when the take up reel is packed full.
"Play accel" function not working. This is the initial jolt of torque provided by the take up motor when play is initiated. Cleaned and inspected both power supplies. Discovered a few molex pins who've lost their plating, specifically on the power transistor umbilical pins. This might be a problem later.
Track 3- Playback signal occasionally dropping out in sync mode.
Repaired frayed sync/record head cable at the molex connector on the "strip board".
Track 11 - Wasn't recording properly, and causing crosstalk noise on neighboring channels. Problem didn't follow the audio boards.
Traced to a bad transistor on the strip board (Q1) which relates to the bias/erase ramp circuit.
Track 18 meter toggling between normal and pinned.
Exercised the meter connections in the meter bridge. These are pressed contacts on .100" pitch housings. It's possible one of the wires is working its way loose too, but couldn't find one.
All channels were metering 2dB off with a 1k sine wave coming in at +4dBu.
Calibrated the "input level" and meters for all 24 channels, +4dBu in and out with the VU at "0".
Tape tension erratic during play mode. The tension arm darting around at a rate relative to the supply motor's rotation, and tape tension strain could be heard with those pulses.
Problem was traced to a bad tachometer on the supply motor (not really a tachometer, but more of a tiny motor/generator). Using a full reel as a flywheel, with the brakes disengaged, the problem could be measured directly at the tach terminals, and the buffered signal ("Absolute Value") showing dropouts in voltage throughout its rotation. The tachometer, should be rebuilt, or replaced. For now, I performed a modification noted by tech, Michael Blackmer, to smoothen the signal (on the analog torque board, .47uF film capacitors in parallel with R13 and R37, and a 47uF 35v bipolar capacitors across the tach inputs (J-13) to act as a low pass filter, and bridge the dropout moments). Double checked the tension balance and transport performance.
Fully calibrated the audio (azimuth, repro, record) to 355nWb/m, 15 ips NAB using SM911. Track 24 underperforming a little.
Auto Locator III - Auto locator intermittently working, while counter continues to work. Fully functional when cold.
Removed the auto locator module, checked regulators, cleaned all the connections, reseated all ICs, re-tensioned a few molex sockets. On the processor board, I discovered a few fractured solder joints on the molex headers, so I reflowed all of them, and the smaller pitch ribbon headers. There was no case ground connection which meant static shock could send the transport into play or fast forward. I was able to tie ground to the chassis via one of the TO-3 regulator socket mounts (not TO-3 case). Recommended returning the ALIII for a replacement since it never worked and was sold as "working".
Other MCI notes-
Fixed a bad soldering job on a replaced electrolytic on a strip board. This might be a more widespread issue because of some lazy work when capacitors were replaced.
Loose barrier strip behind the head shield solenoid reattached.
Otari MX55-
Did some preliminary evaluation. Calibrated it to 355nWb/m using ATR tape at 15ips NAB. Noted some extreme wow and flutter. Suggest lubricating the capstan and possibly replacing the pinch roller.
Work on a Trident TSM 40 console and wiring-
Various pro tools outputs not making it to the patchbay properly. The patchbay connections are 96 pin DLs mounted to a difficult-to-reach bottom of the patchbay rack. They are jumpered, via short snakes, to a panel on the rear of the console with EDAC connectors, labeled 24-track in and out. This might have been done to make switching back and forth from different recorders a simpler process than reaching into the underbelly to access the DL connectors. Not sure.
The PT output problems were sourced to a couple broken wires in the EDAC connectors (weak strain relief), and several DL pins (including channel 7) which were not seating in the male housing due to their retaining tabs being worn down. I reattached the broken wires, and zip-tied the loose DL wiring to neighboring wiring get more support. I recommended replacing the short EDAC to DL umbilicals under the console and just directly wire what's needed to new DL connectors.
Checked power supply. The bipolar rails were a little low at around ±17v, if the desired level is ±18v. The plan is to get an upgraded supply, and use this as a backup.
Noted a few channels with noisy switches (polarity, eq on, filter, line/mic, and insert).
Channel 13 - cleaned by removing the switch plungers, and cleaning with a q-tip on the removed wiper contacts, then exercised.
EMT 162 plate crackling noises.
Couldn't get it to crackle. Cleaned connections, exercised switches and pots, took notes on potentially re-capping the amp later.
Work on MCI JH24 -
Tape won't play without a little push, when the take up reel is packed full.
"Play accel" function not working. This is the initial jolt of torque provided by the take up motor when play is initiated. Cleaned and inspected both power supplies. Discovered a few molex pins who've lost their plating, specifically on the power transistor umbilical pins. This might be a problem later.
Track 3- Playback signal occasionally dropping out in sync mode.
Repaired frayed sync/record head cable at the molex connector on the "strip board".
Track 11 - Wasn't recording properly, and causing crosstalk noise on neighboring channels. Problem didn't follow the audio boards.
Traced to a bad transistor on the strip board (Q1) which relates to the bias/erase ramp circuit.
Track 18 meter toggling between normal and pinned.
Exercised the meter connections in the meter bridge. These are pressed contacts on .100" pitch housings. It's possible one of the wires is working its way loose too, but couldn't find one.
All channels were metering 2dB off with a 1k sine wave coming in at +4dBu.
Calibrated the "input level" and meters for all 24 channels, +4dBu in and out with the VU at "0".
Tape tension erratic during play mode. The tension arm darting around at a rate relative to the supply motor's rotation, and tape tension strain could be heard with those pulses.
Problem was traced to a bad tachometer on the supply motor (not really a tachometer, but more of a tiny motor/generator). Using a full reel as a flywheel, with the brakes disengaged, the problem could be measured directly at the tach terminals, and the buffered signal ("Absolute Value") showing dropouts in voltage throughout its rotation. The tachometer, should be rebuilt, or replaced. For now, I performed a modification noted by tech, Michael Blackmer, to smoothen the signal (on the analog torque board, .47uF film capacitors in parallel with R13 and R37, and a 47uF 35v bipolar capacitors across the tach inputs (J-13) to act as a low pass filter, and bridge the dropout moments). Double checked the tension balance and transport performance.
Fully calibrated the audio (azimuth, repro, record) to 355nWb/m, 15 ips NAB using SM911. Track 24 underperforming a little.
Auto Locator III - Auto locator intermittently working, while counter continues to work. Fully functional when cold.
Removed the auto locator module, checked regulators, cleaned all the connections, reseated all ICs, re-tensioned a few molex sockets. On the processor board, I discovered a few fractured solder joints on the molex headers, so I reflowed all of them, and the smaller pitch ribbon headers. There was no case ground connection which meant static shock could send the transport into play or fast forward. I was able to tie ground to the chassis via one of the TO-3 regulator socket mounts (not TO-3 case). Recommended returning the ALIII for a replacement since it never worked and was sold as "working".
Other MCI notes-
Fixed a bad soldering job on a replaced electrolytic on a strip board. This might be a more widespread issue because of some lazy work when capacitors were replaced.
Loose barrier strip behind the head shield solenoid reattached.
Otari MX55-
Did some preliminary evaluation. Calibrated it to 355nWb/m using ATR tape at 15ips NAB. Noted some extreme wow and flutter. Suggest lubricating the capstan and possibly replacing the pinch roller.
Work on a Trident TSM 40 console and wiring-
Various pro tools outputs not making it to the patchbay properly. The patchbay connections are 96 pin DLs mounted to a difficult-to-reach bottom of the patchbay rack. They are jumpered, via short snakes, to a panel on the rear of the console with EDAC connectors, labeled 24-track in and out. This might have been done to make switching back and forth from different recorders a simpler process than reaching into the underbelly to access the DL connectors. Not sure.
The PT output problems were sourced to a couple broken wires in the EDAC connectors (weak strain relief), and several DL pins (including channel 7) which were not seating in the male housing due to their retaining tabs being worn down. I reattached the broken wires, and zip-tied the loose DL wiring to neighboring wiring get more support. I recommended replacing the short EDAC to DL umbilicals under the console and just directly wire what's needed to new DL connectors.
Checked power supply. The bipolar rails were a little low at around ±17v, if the desired level is ±18v. The plan is to get an upgraded supply, and use this as a backup.
Noted a few channels with noisy switches (polarity, eq on, filter, line/mic, and insert).
Channel 13 - cleaned by removing the switch plungers, and cleaning with a q-tip on the removed wiper contacts, then exercised.
EMT 162 plate crackling noises.
Couldn't get it to crackle. Cleaned connections, exercised switches and pots, took notes on potentially re-capping the amp later.
Re: GReg-Electrical Tech Journal Redux
114Trying to get more switches for the direct boxes shipped before 2050.
Ampex ATR #2
Capstan issues. More later,
On the Capstan Servo board, dead R32 causing tachometer amp A20 to go into maximum gain, corrupting the tach signal to the rest of the circuit.
Neotek Elite-
Last stereo modules back in the console after replacing the pushbutton switches!!! All 51 mono and 8 stereo channels DONE!!! Thanks to JSP for all the help!
Ampex ATR #2
Capstan issues. More later,
On the Capstan Servo board, dead R32 causing tachometer amp A20 to go into maximum gain, corrupting the tach signal to the rest of the circuit.
Neotek Elite-
Last stereo modules back in the console after replacing the pushbutton switches!!! All 51 mono and 8 stereo channels DONE!!! Thanks to JSP for all the help!
Re: GReg-Electrical Tech Journal Redux
115Neotek Elite-
Aux 4 output full of DC and shit...
Dead patched what it was normalled to for the rest of my session. Got done late the last night (now), and was curious. Carefully pulled the Aux Master module out, and unplugged the power to it, then swapped the summing amp with another (aux 3). Problem followed that. Replaced the bum note. All good.
But still... Don't hot swap. No joke, kids.
Nighty.
Aux 4 output full of DC and shit...
Dead patched what it was normalled to for the rest of my session. Got done late the last night (now), and was curious. Carefully pulled the Aux Master module out, and unplugged the power to it, then swapped the summing amp with another (aux 3). Problem followed that. Replaced the bum note. All good.
But still... Don't hot swap. No joke, kids.
Nighty.
Re: GReg-Electrical Tech Journal Redux
116Studer A820MCH MkII -
Chan 20 low output at 30Hz on input.
Replaced all the electrolytics on the NRS control board, including a wrong replacement. Found one which measured at 3uF (should be 47uF).
Recapped the Generator Unit board.
Checked that the Repro Preamp boards had been recapped.
Researching a switch mode power supply to provide the bulk 50v DC to the rest of the machine. Needs to be dead quiet, flat as glass and provide 20+ amps, and fit inside the carcass of the old supply.
Chan 20 low output at 30Hz on input.
Replaced all the electrolytics on the NRS control board, including a wrong replacement. Found one which measured at 3uF (should be 47uF).
Recapped the Generator Unit board.
Checked that the Repro Preamp boards had been recapped.
Researching a switch mode power supply to provide the bulk 50v DC to the rest of the machine. Needs to be dead quiet, flat as glass and provide 20+ amps, and fit inside the carcass of the old supply.
Re: GReg-Electrical Tech Journal Redux
117Studer A820MCH Mkii-
Noisy acoustic hum from the main power supply (unregulated DC supply at the base of the machine). Output voltage is stable, and correct.
2 of the 3 power transformers causing this. Tested the transformers individually, and all the voltages measure correct values, unloaded and loaded by the rectifier. The noise was produced whenever they were simply powered up. Double checked the inductances of all the windings against the silent transformer, the two noisy ones measured the same. I'm going to set this aside for a bit. Those transformers are roughly $1400 a piece, and we have a spare complete supply.
-Elsewhere-
Someone sent me a pair of racked up Neotek SII channels to check out. The power supply was a Power One module mounted in a cheap plastic box which shattered under the PSU's weight during shipping. Rehousing it in a more sturdy metal box.
Sony MXP3000 input channel has no bus or direct output.
Hybrid differential output amp dead, along with surrounding components. Replaced it all with spares and new parts.
Noisy acoustic hum from the main power supply (unregulated DC supply at the base of the machine). Output voltage is stable, and correct.
2 of the 3 power transformers causing this. Tested the transformers individually, and all the voltages measure correct values, unloaded and loaded by the rectifier. The noise was produced whenever they were simply powered up. Double checked the inductances of all the windings against the silent transformer, the two noisy ones measured the same. I'm going to set this aside for a bit. Those transformers are roughly $1400 a piece, and we have a spare complete supply.
-Elsewhere-
Someone sent me a pair of racked up Neotek SII channels to check out. The power supply was a Power One module mounted in a cheap plastic box which shattered under the PSU's weight during shipping. Rehousing it in a more sturdy metal box.
Sony MXP3000 input channel has no bus or direct output.
Hybrid differential output amp dead, along with surrounding components. Replaced it all with spares and new parts.
Re: GReg-Electrical Tech Journal Redux
118Recapped, tested and installed a spare Studer A820MCH mki power supply in the mkii machine (they're compatible, though it was a slightly tighter fit than I expected). The new 68,000uF caps were slightly taller than the original which caused some scrambling for adaptive hardware. Being in a big city is handy for getting very specific, odd ball metric standoffs and screws delivered within 12 hours. Thanks McMaster.
Studer A820MCH power supply
After digging into the chassis to release and the old capacitors and secure the new in the clamps, with apparently hard to reach bolts and nuts, I discovered there are slots on the side to let you loosen those in a matter of seconds. :u
Studer A820MCH power supply
The supply is operating nice and silent, in the new machine.
Worked on ATR #1 for use in the transfer studio, "studio C".
Discovered the 120Hz noise on the audio survived the power supply rebuild. Updated original post about that with the solution.
viewtopic.php?p=846907#p846907
Reel motors won't enter servo mode after my power supply fix.
When working on the 120hz issue. I remounted the power supply pcb in a way that pushed wires into the dynamic brake relay (tight space).
I had most of the machine apart chasing red herrings before I discovered this. I was lead to believe the two power transistors or their protection diodes for the supply motor amplifier were faulty. Ended up replacing the perfectly fine MDA power transistors with shiny new ones.
More when I have energy....
Atr power supply
After digging into the chassis to release and the old capacitors and secure the new in the clamps, with apparently hard to reach bolts and nuts, I discovered there are slots on the side to let you loosen those in a matter of seconds. :u
The supply is operating nice and silent, in the new machine.
Worked on ATR #1 for use in the transfer studio, "studio C".
Discovered the 120Hz noise on the audio survived the power supply rebuild. Updated original post about that with the solution.
viewtopic.php?p=846907#p846907
Reel motors won't enter servo mode after my power supply fix.
When working on the 120hz issue. I remounted the power supply pcb in a way that pushed wires into the dynamic brake relay (tight space).
I had most of the machine apart chasing red herrings before I discovered this. I was lead to believe the two power transistors or their protection diodes for the supply motor amplifier were faulty. Ended up replacing the perfectly fine MDA power transistors with shiny new ones.
More when I have energy....
Re: GReg-Electrical Tech Journal Redux
119ATR Reel Servo board-
Replaced the missing transistor I pulled to fix the power supply described above.
-Elsewhere-
Recapped the Studer A820MCH power supply at my place. This took a fraction of the time the other one took now that I know about the capacitor clamp access slots.
Replaced the missing transistor I pulled to fix the power supply described above.
-Elsewhere-
Recapped the Studer A820MCH power supply at my place. This took a fraction of the time the other one took now that I know about the capacitor clamp access slots.
Re: GReg-Electrical Tech Journal Redux
120Someone bought a 17 year old MS Matrix which wasn't working right.
I updated to the later design before testing for problems. All good.
I updated to the later design before testing for problems. All good.