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GReg/Electrical Tech Journal

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

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Re: GReg/Electrical Tech Journal

Postby greg on Wed Jul 01, 2020 2:44 pm

-Home-

Sony MXP3036-

Wein Eq causing a phase shift and roll off of low frequencies when switched off.

Bad Elna 220uF bipolar cap in the bypass path. The Elna caps seem to be failing faster than the Nichicon ones in that board.

Neve 3114 modules-

Taking apart and cleaning two 3 deck, 24 position gain switches. What a pain.

Cleaning EMI Painton switches.

Searching for a replacement photocell for a Scully 8 track "click silencer" board. Original part number is Clairex CL704L.
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Re: GReg/Electrical Tech Journal

Postby greg on Thu Jul 02, 2020 5:50 pm

Replaced 2 Elite channels (15 and 17) with spares. They had intermittent signal path switches. Will clean later.

Tested out a homemade wiring harness for the ATR 2-track to be used as a 4 track (without the four I/Os). This is basically bypassing the Meter-i/o modules. Worked.
We are able to do 4-track transfers now!
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Re: GReg/Electrical Tech Journal

Postby greg on Sun Jul 05, 2020 8:15 pm

ATR (number 3) in Studio A-

Right meter pinned at normal levels after turning machine on.

R21 (meter calibration trimpot) extremely intermittent. On the bench, I replaced most of the active parts, and checked everything passive in the path of the meter circuit, but it ended up being this thing, which is puzzling.

Did a complete I/O calibration for both channels when everything was done.
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Re: GReg/Electrical Tech Journal

Postby greg on Fri Jul 10, 2020 3:50 pm

Bryston 3b amp -

No action on one side
.

One of the 6(!) mains fuses blew (unconventional power supply design). I replaced the fuse, and the trouble channel worked intermittently.
It ended up being the power switch. Why would one channel work if the power switch wasn't working? Well, the amp basically has two completely discrete power supplies, one for each channel. The mains switch is a DPST that switches on both separately. One half of the switch was bust. Why do they do this? not totally sure. Anywho, replaced the switch with a 15 amp guy, not changing anything in the circuit.

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Re: GReg/Electrical Tech Journal

Postby greg on Thu Jul 16, 2020 5:20 pm

UREI LA-22 and LA-12-

Switches causing intermittent action and distortion. Dried root beer everywhere.

Cleaned the syrup off, and replaced switches in both compressors.

LA-22 left channel Auto function flickering on and off, when It should be off.

One of the solder joints looked broken, or cold on the switch deck of the pot/switch gang. Re-flowed the joint, all good...
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Re: GReg/Electrical Tech Journal

Postby greg on Fri Jul 24, 2020 5:15 pm

Neotek Elite-

Switch intermittencies with Channels 15, 17, and 21.

Replaced problem channels with spares.

Channel 17 test - pulled all the switch plungers and cleaned contacts thoroughly with 90+% alcohol. Sprayed switch insides with MS-738 contact lube, immediately reassembled and exercised the switches. I used this channel to replace channel 21 on the board. Everything switches smooth and quiet now, but let's see what it's like in a few months. The Stabilant treatment didn't seem to work perfectly, so I'm going to try some other products.
On the next channel, I'll try EML. I'm disqualifying any contacts that show signs of missing plating, which is not an obvious thing to see on the insides of a 4PDT cavity.


Ampex ATR custom 1/4" 4-track head-

Static pops on track 4.

I recognized this sound as the repro static noise that happens with poorly grounded head cores. Measuring the face of the head (CAREFULLY), I saw that they were grounded ok, but the headstack itself was poorly grounded to the mounting block, where the ground is coming from. I temporarily taped some copper braid across both pieces to get through the transfers we're doing. Need a more permanent solution...
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Re: GReg/Electrical Tech Journal

Postby greg on Mon Jul 27, 2020 4:43 pm

Steve's birthday mixing session was plagued by ATR mishaps.

Ampex ATR #1 -

Low Frequency rumble on the output of the Main Audio PWA, only in Repro mode.

I traced it to the makeup/buffer amplifier section post PADNET PWA eq and level adjustments. Replaced A1 (318H) and all is quiet again.

Spare ATR Audio board #3-

Nothing recording, Bias and Erase led's light in record mode.

Things were actually recording, but the Repro Gain pot was intermittent working. Putting pressure on it snapped the signal back and forth from nothing. Replaced with a new one.

Spare ATR Audio board #1-

Bias Norm pot erratic while adjusting.

Same deal. The pot was bunk. I checked for a broken leg or solder joint, but no signs. Replaced.

All ATR Audio Spares confirmed working.

Machine stopped being able to play at 30 IPS while trouble shooting the spare audio boards. Motor would speed forward like in wind mode when you hit play. Worked perfectly at 15 IPS.

Chased things down with the Reel Servo board unplugged, allowing you to test the capstan motor without needing to thread any tape.

- Cleaned and checked speed selectors switch...
- Swapped Capstan Servo board...
- Pulled both audio boards (including spare under test), and 30 IPS worked perfectly.
- Installed only the spare under test (spare #3) and the problem came back.
Seeing where the speed logic lines (SSA SSB) meet the channel, I replaced A1 and A2 (4011) on the Audio PWA daughter board. I did try to reseat the two before replacing them since they were socketed, but replacing them was the thing that worked. I was curious which one was the culprit, but this was a problem I need to get over with to get on with the other problems...
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Re: GReg/Electrical Tech Journal

Postby greg on Tue Jul 28, 2020 9:30 pm

-Elsewhere-

Ongoing Neve 5300 series console 3114/5 module recap and restoration...

Replaced an Elma gain switch in one module that was destroyed. The plating was scratched off the contacts on 2 of the 3 decks. The whole switch and wiring loom to it was caked in green slime. The heat shrink and insulation around the wires crumbled off like dried rubber. A total mess. The new switch in it's golden, gleaming newness was such a blessing to install. I also rewired everything from the transformers, and pcb.

Another 3114 module-
Broadband gain in the 8.2kHz position of the presence eq band (not the expected bell curve peaking at 8.2k). Channel oscillates when that band, in that freq is at max gain position.

C41 (5.6nF styrene cap) was measuring in the 10s of uFs. Replaced it, but the oscillation was still happening. Trying to troubleshoot, I swapped the amp associated with that band (A5) with the Bass band amp (A6). The sockets were a bit grimey due to some sweaty looking heat shrink on cables in contact with the opamp inputs. Yeah, sweaty. Anywho, the oscillation went away when after I cleaned up and moved the wires. I triple-checked the eq to make sure things are working right.

Cleaned another intermittent 1081 gain switch with
alcohol first to clean out the old cleaning product, then
deoxit to clear off some of the blackened parts,
confirmed the plating was still in tact, then
alcohol to clean off the deoxit, then finally
Electrolube EML to coat the parts.
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