Problem (freelance)-
Altec 525 power supply (for 165 and 175 mics) not functioning after being dripped on.
Solution-
Some how the power transformer fried. More to it, the high voltage winding fried. All the passive components in the PSU were working fine. The high voltage winding, unloaded, looked ok. Whenever it was connected to any load, it had nothing. I replaced the transformer, cleaned the insides, replaced B+ rectifier, and it is all ready for action.

Related to this,
Problem-
Old ebay Altec 175 sounding like ass (bought on ebay a few years ago, was in a small pile of projects to do when the time comes (since there are 5 working ones in the studio already)).
Solution-
Some retard wired a the fancy mogami tube mic cable all retarded on it.
Long story short, the filament return conductor was shorted to ground because of sloppy soldering. This can't happen since the filament sits on the B+ voltage. See schematic.
He or she (I'm guessing it's a he since dudes do this stupid shit) opted not to use the larger gage conductors intended for the filament, but rather used the light gage audio wires. http://www.mogamicable.com/Bulk/micr_ca ... emicc.html
The mic was dark and shitty sounding. I snipped off the ends and re-soldered them all nice and clean. Mic sounded decent, but made horrible thundering noises when I moved it. I took apart the capsule housing, and discovered the back plate was loose (heard a rattle before). That was secured. I thought the capsule might have been torn, but it looked almost perfect (after 40 so years!).
Wha-bam! It sounds great now. It worked in a session this weekend with great results.

greg wrote: It worked in a session this weekend with great results.[/color]

What did you use it on?

otisroom wrote:

greg wrote: It worked in a session this weekend with great results.[/color]

What did you use it on?

Snare/Drums

1/15/8
Problem-
Schoeps 221b stereo power supply (retrofitted with our standby delay tube power supply board) is blowing fuses.

Solution-
Checking circuit board, everything looked perfect, no overheating, shorts, or any other signs of damage.
The original IEC power connector made a really loose connection to typical power cables. The power connection would flicker and arc depending on the position of the cable. Wiggling the power cable, with the power on, I could cause the fuse to blow.
I replaced the IEC connector with a new one. Very secure contact now.
I'm glad it wasn't my board.

Problem-
Digidesign 192 i/o
• Input 7 has a higher than acceptable level of thermal/wind noise (A and B, no difference)
• Input 8 passes no signal (A, B, +4, and -10 input). I could trace signal past the differential input op amps to the transistor farm (where the Q150s, and 4 t0-92 diodes live). At that part of the board problems occur.

Solution-
Not having a schematic, I just replaced what transistors I had in stock, and hoped for the best. No luck.
Off to Ground Control for repair.
This was kind of a lesson in discipline. I promised myself I would only spend 2 hours working on it before giving up, and sending it off. I ended up wasting most of the day, leaving me no time to finish anything else on my list of things to do. I kept thinking I was so close. The previous experience of fixing one of those things egged me on.
Oh well.
1/31/8 - Replacement board installed/tested well.
Ordered some unrelated parts for the Furman upgrade.

Problem-
Wasp keyboard not working, and falling apart.[/color]

Solution-
Loose battery leads may have bumped up against something? Removed them (installed a permanent wall wart a while ago).
There was a bit of a hum on the out put so I replaced the very small value electrolytic caps in the power supply section with larger ones (battery powered things don't need much in the way of filter caps). There was a total of 6uF on the supply. Now there is about 470uF. This deals with the wall wart's ripple well, without killing it on power up.
I also mounted the keyboard and main pc board to the case with real screws and stand-offs. This thing wasn't meant to last more than a year of child's play. [/color]

Problem-
Neotek Elite's rear deck speaker send intermittently fails on one channel.[/color]

[color=blue]Solution-
Exercised connections to monitor board, and relay control lines. Will re-punch sends on the punch block if this doesn't work. [/color]

I saw Note By Note, the Steinway piano manufacturing documentary yesterday. I totally recommend it for any of you crafty folks.

Retrofitted two Neumann/Geffel N61 mic power supplies with nice xlr connectors and IEC power outlet. I have to order replacement power transformers for the American standard.

Finally finished the faceplate for my two channel Normaphone preamp (living in a Sytek box right now).

Problem-
Mellotron keys inconsistent action and level.

Solution-
Went through the entire thing with the key setup guide I found on this site. The keys seem stiffer now, maybe that is how it should be. Notes are consistent now.

Ordered some cable samples for the furman project.

Problem-
Channel 12 on the Elite always sends to Aux A.

Solution-
Channel replaced with spare.
Opened dual pot (AB level) remounted A's wiper disc so that it made better contact with the resistive track.

Channel 5 of the Elite has high input level relative to the pot position.

Same solution. Wiper was not making good contact with the track. Both pots must have been whacked sideways to jar this loose.

Traynor Mono Block - B distorted all the time.


High wattage .27 Ohm resistor (in series with the emitter of one of the 4 output transistors and output) broke its leg. These resistors are heavy so it could have happened during a fall. With one of the push pull transistors out of the circuit, this caused power weakness in one of the polarities and distortion at low levels. An overheated 470 ohm feedback resistor, and crazy high signal level at that same emitter (relative to the other transistors) lead me to this resistor (which looked fine). I saw the resistor was busted off the board when I started poking and pushing.


Replaced missing retaining ring on a AKG 451. This is what keeps the guts from being pulled out when removing the mic cable.

2/19/8

Blown RCA 74 sent off to Enak.
Back 4/9/8

Edge connectors cleaned on Neotek SeriesII Cue/Echo master module.

Search for more cable for furman upgrade. Right now, the best candidate is Mogami's W2871