home studios equipment staff/friends booking/rates for sale forum contact

GReg/Electrical Tech Journal

All your geeky questions about electronics, microphones, tape machines, etc.

Moderators: kerble, Electrical-Staff

Postby greg on Wed Mar 02, 2005 5:45 pm

3/1/5
Problem-
Neotek Elite talkback button not working well.

Solution-
Last straw.
I removed the faceplate of the monitor/master section, and handed it off to a machinist friend of ours. He is cutting a larger hole in the place of the old talkback hole to fit an EAO switch. This switch will last longer.

3/4/5 Done. Thanks Andy
Problem-
The band Mono have a busted 4x12" cabinet. It sounds as if the speakers are blown.

Solution-
It is one of those newer marshalls with the stereo switch on the speaker jack panel. The 1/4" jack panel was busted and the switch was making a bad, intermittent connection. This made it sound like the speakers were blown. We had one of those jack panels w/ circuit board sitting on the shelf here so I used it. I performed a few frequency sweeps (low freq.) to check the speakers. They were fine.
Last edited by greg on Fri Mar 04, 2005 9:18 pm, edited 2 times in total.
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby greg on Wed Mar 02, 2005 5:49 pm

3/2/5
Problem-
RCA 74 had dramatic volume swings.

Solution-
Ribbon was stretched. It was flapping back and forth. I sent it off to Enak for repair.


Back, and beautiful job Clarence.
Last edited by greg on Wed Apr 06, 2005 8:17 pm, edited 2 times in total.
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby greg on Fri Mar 04, 2005 9:17 pm

3/4/5
Problem-
Neotek Elite buss 26 oscillating occasionally.

Solution-
Still finding that out.
I replaced the channel strip (with "spare 3") so I could look at the original upstairs. The replacement wasn't working right. It wouldn't cal to the right o/p level and had a high freq oscillation on it. After probing around, It seems as if there might be something wrong with the ribbon cable connector.
More later.


The umbilical coming off the bus ribbon to the input of the bus amp (located on the channel strip) was loose in the connector. It was a punch connection that had come loose. The poor contact caused the bus amp to feed back. I re-punched the wire, then wiggled it a bunch to see if it would fail again. It didn't, so, so long motherfucker (oscillation).

Spare #3 channel- There was a cap soldered in parallel to the feed back resistor in the bus amp that had a loose leg touching another resistor. This was either missed at the factory or bumped in transport. I resoldered the M-Fer and it works as it should now.
Last edited by greg on Fri Apr 01, 2005 4:16 am, edited 3 times in total.
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby greg on Wed Mar 09, 2005 1:29 pm

3/8/5
Problem-
Ampex ATR #1 buzzes acoustically from the transport, wont unthread when you press the edit button, .... more later
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby greg on Thu Mar 24, 2005 3:10 pm

Problem-
The Flying Faders on the Elite are showing random errors. The record, select, and solo functions would randomly fire on different faders. It started happening once or twice a day. After a while, It was once every few hours.

Solution-
I tried to calibrate the gain on the fiber optic transmitters as per the manual's instructions. I couldn't get the desired setting. This would either be because the cable was bent too much (was not), or the transmitter/receivers have started to burn out. I ordered a replacement kit from Martinsound, which included newer versions of the old trans/receivers.
A week after installing the new parts, there have been no glitches.


- Also cleaned intermittent "group" button on master module.
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby greg on Tue Mar 29, 2005 8:59 pm

Brief
Problem-
ATR #2 has speed irregularities.

Solution-
Speed select switch dirty. I figured that out when I was correcting the tension on the machine and switched the speed. After switching it there were creaking sounds coming from the capstan motor. These are the same creaking sounds it makes when the motor goes in and out of phase lock.

The capstan is driven by a phase lock loop (PLL) circuit which is how most capstans are in modern tape transports. It drives the capstan faster or slower to match the motor tachometer to a reference frequency. When the tach pulse frequency maches the reference frequency it has achieved "lock"

This noise happens also when there is a poor signal derived from the capstan tach optics.
The poor switch contact caused a glitch in the 2 bit signal that determines speed throughout the machine.
I cleaned it very carefully.

Problem-
Garnet BTO Special: tremolo too fast.

Solution-
Changed pot . . . Russ. . .
We're going to field test it for a while.

Problem-
Garnet BTO Special: Stinger function always on.

Solution-
Short on footpedal jack. Fixed


Problem-
GLM100 not working

Solution-
1 of the 2 wires going to the capsule ripped out of the solder pad on the tiny circuit board. Repaired damaged traces, and re-trimmed the cable.
Last edited by greg on Wed Apr 06, 2005 8:04 pm, edited 2 times in total.
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby greg on Tue Apr 05, 2005 6:32 pm

RCA BK-5 has a blown ribbon and it is off to Enak.

Ampex ATR -102 #2
Calibrated the I/O modules, and adjusted the tensions.
Problem-
Neotek Elite
Channel 17 was sending signal to Aux B while the level was set to 0.
Channel 20 was never sending signal to Aux 3 at any level setting.
Channel 22 was sending a little signal to Aux 1 while the level was set to 0.


Build a sentence out of the letters from words that aren't common in all 3 sentences above (keep #s).

Solution-
I reworked the wiper disks for those pots so they made better contact with the resistive elements.
Last edited by greg on Wed Apr 06, 2005 8:18 pm, edited 2 times in total.
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby greg on Wed Apr 06, 2005 7:43 pm

4/6/5
Problem-
Noisy Altec 150 microphones (mostly wind and waterfall type noise).

Solution-
Step 1: Opened them up and cleaned all the contacts and pins. The noise was still there.
Step 2: Replaced the tubes.
Replacing the tubes did the trick. They are now going to be left on over night for an endurance test.


Searched for some good, quiet pots for the MS Decoder prototypes. Noble self-cleaning carbon pots look good but are bought on a custom order basis. They are unique in that they are long lasting, quiet carbon pots. Carbon pots have better contact and less distortion in most audio circuits. Unfortunately they usually get scratchy over time.
I am trying a couple different ones.

One of the Coles 4038 has a blown ribbon.
These are pictures of the ribbon. If you look carefully you can see the tinfoil like ribbon resting at the mouth of the "c" shaped magnet. The ribbon should be corrugated and taught. This one is stretched flat and saggy.
Image

Image

Image
Last edited by greg on Thu May 08, 2008 1:49 am, edited 8 times in total.
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby MTAR on Thu Apr 07, 2005 9:24 am

greg wrote:4/6/5
One of the Coles 4038 has a blown ribbon.
These are pictures of the ribbon. If you look carefully you can see the tinfoil like ribbon resting at the mouth of the "c" shaped magnet. The ribbon should be perforated and taught. This one is stretched flat and saggy.
[/img]


Greg,
the picture, she is not there. I fear what she may look like though, for it may make me so sick like those pictures of tar-ridden lungs or herpes infested genitals from health class.

mtar
Michael Gregory Bridavsky

Russian Recording
Memory Map
Push-Pull
User avatar
MTAR
Supreme Commander at the Forefront
Supreme Commander at the Forefront
 
Posts: 1965
Joined: Wed Jun 04, 2003 10:04 am
Location: bloomington, IN

Postby steve on Thu Apr 07, 2005 11:58 am

greg wrote:The ribbon should be perforated and taught. This one is stretched flat and saggy.


You mean corrugated and taut. Perforated and taught is what the students at a Rwanda grade school were. And hacked to pieces with a machete.
steve albini
Electrical Audio
sa at electricalaudio dot com
Quicumque quattuor feles possidet insanus est.
User avatar
steve
Present-day God
Present-day God
 
Posts: 9356
Joined: Wed Jun 04, 2003 3:25 pm
Location: chicago

Postby greg on Thu Apr 07, 2005 12:27 pm

oops!
Thanks
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby greg on Mon Jul 11, 2005 6:07 pm

7/11/5
Problem-
AKG C-24 top capsule pattern permanently cardioid. The pattern select switch has no effect.


Solution-
There was a problem with the power supply. The rear capsule bias resistor connecting the pattern select switch to the top capsule broke off. Curious. It may have been dropped. Either way, I replaced the resistor and checked the PSU over. Things are good now.


Here are the guts. This is the first mic PSU I built. Notice the fancy shielding between the transformer side and regulator/audio side. Make fun if you like.
Image
Image
Last edited by greg on Thu May 08, 2008 1:52 am, edited 2 times in total.
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby chachi on Thu Jul 28, 2005 11:04 am

ha! ha!

Image
chachi
scout
scout
 
Posts: 20
Joined: Wed Jul 14, 2004 7:32 pm

Postby greg on Fri Aug 12, 2005 8:30 pm

8.2005
Problem-
Schoeps 221b not working.


Solution-
Mic cable had a frayed shield that would short out pins on the connector. I rewired the connector putting heat shrink isolation on each pin's solder post.
I performed my grounding mod on the mic as well (allen screw and star washer in place of one of the three set screws holding the body to the connector)
.

Cleaned up and shortened Sony C-37 cable that was damaged.
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby greg on Thu Aug 18, 2005 5:55 pm

8/14/05
Problem-
Cat 5 panel connectors punched through panel in Alcatraz.


Solution-
Replaced connector.


I know, boring.
Something else happened.
I got the first set of custom made boxes for the MS decoder, and set up a work station for making those.
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby greg on Mon Aug 29, 2005 7:18 pm

8/29/5
Problem-
ATR (new) Rumbling noise on Right Channel when machine was in stop, and monitoring "Repro." The problem follows the Main Audio PWA and not the PADNET PWA. This does not effect the recorded signal. Replacement board is temporarily installed.


Solution-
On the Main Audio PWA:
Replaced A3 (1st op amp after the repro head and usually where that type of noise comes from). The noise takes a bit of time to develope, so we'll check her out later.

8/31 Noise was still there. I replaced the transistor on the front-end of that repro preamp. Again, noise.
Replaced A2 (audio card output amp going to the I/O module).

10/3/5
Discovered that input signals bleed to the output when the channel is set to Repro. Only low frequencies pass <60Hz. This clues me into the possibility that one of the switching FETs failing. I replaced Q2, Q3, and Q20. These are FETs that switch the output audio between tape and input signals located immediately before the PWAs output amp. When I replaced Q20 (sends input signal to ground, muting it before card o/p amp) the bleeding stopped. I am hoping this is also the source of the rumbling noise. I will check for that tomorrow.

10/5/5
Replaced A1 (op amp following dual transistor Q1). The only active component left in this signal chain is Q1. This is the front end of an amp section (including A1) that supports the signal coming from the PADNET PWA. The part # is 2N3536, and is no longer available from my 1st choice suppliers. When the ATR Service folks return from AES I'll get a replacement part from them. This problem has taken too long.
Last edited by greg on Thu Oct 06, 2005 1:42 pm, edited 3 times in total.
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby greg on Mon Sep 19, 2005 6:08 pm

9/19/5

Problem-
Royer 122 S/N 1112 has a violent crackling noise which occurs randomly.


Solution-
After confirming that it was the mic (swapping cables, and console channels). We sent the thing back to Japan for repair.


Problem-
AKG C-24 top capsule positioning puck pops loose when you try to change it (you use this to rotate and change the angle of the top capsule in relation to the bottom capsule). It is also the top of the microphone.


Solution-
Removed top screen and re-tightened the mounts. I also added a little grease to the rubbing parts so that it operated a little smoother.


-Blown M-88 is sent off to Beyerdynamic for repair. It was defeated by a kick drum in a session.
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby Rodabod on Mon Sep 19, 2005 8:21 pm

greg wrote:Problem-
Royer 122 S/N 1112 has a violent crackling noise which occurs randomly.


Solution-
After confirming that it was the mic (swapping cables, and console channels). We sent the thing back to Japan for repair.



Are Royer mics made in Japan? I thought they would have been made in the US.
User avatar
Rodabod
Heaven-Sent Hero
Heaven-Sent Hero
 
Posts: 6130
Joined: Sat Apr 10, 2004 2:14 pm
Location: London

Postby greg on Tue Sep 20, 2005 3:57 pm

Oh No!
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

Postby greg on Fri Sep 23, 2005 7:54 pm

Yes they are proudly made in the U.S. I was making a funny.

9/23/5
Lexicon pcm 70 not working. It's input meter is constantly max'ed out, and there is no effected output. The digital bypass works, and the digital "mix" function does seem to work except that there is no effect to mix with it. The programs and display act as though nothing is wrong.


Solution-
Normally I would pass this off to Jim Fabiano in NJ but he's not available.
I need a schematic!
Lexicon all but denies their affiliation with their former flagship product. They want nothing to do with helping people on this (thanks Harman Pro). You'd think they could make a killing off repairs seeing how popular this thing was back in the day. This reminds me of another popular digital room simulator I have problems with . . .


1/24/6
Jim's back,
Sent it in, Jim fixed/replaced a proprietary part in the "digital circuit."
Whatever.
It's fixed now.
Last edited by greg on Thu Jan 26, 2006 11:21 pm, edited 2 times in total.
User avatar
greg
Man with Encyclopedic Knowledge
Man with Encyclopedic Knowledge
 
Posts: 5130
Joined: Wed May 14, 2003 7:26 pm
Location: Chicago

PreviousNext

Return to Tech Room

Who is online

Users browsing this forum: No registered users and 12 guests