sweetbeats said:
I pulled my rec/repro amp cards last night and visually inspected them and dribbled deoxit on the multi-pin connectors, seated and re-seated. I then proceeded with the overall record frequency response calibration.
As the manual says to do I started with the repro head (e.g. loaded blank tape, connected +4dBm test signal, recorded 40Hz, 100Hz, 1kHz, 10kHz and 20kHz test tones on each track while monitoring the repro head and watched the level response to ensure that it was between +/-3VU for each track at each frequency). After a little tweaking of the hi and low record eq pots (R208 and R203 respectively) I was within +1 ~ -1.5 through the test range. I had some problems with track 6...at first I was getting *totally* unstable response...the level would start at -1 and slowly drop to -6...I'd stop and try it again and it would creep up and then drop down...I reseated the amp card...same thing...swapped cards for channels 5 and 6 and the problem followed the card. Then I tried gently manipulating the card while recording and was able to get it stable by gently applying pressure to the right at the bottom of the card. It was stable without pressure after that. Hmm...don't like that.
Then I did the sync head (e.g. same procedure but record the tones while monitoring the sync head and then watch the response on playback. This was all A-OK (which it should be after making the adjustments on the repro side), until 20kHz...I'll attach some video files shortly.
Basically, when I put the 20kHz test tone into the 58, as I should expect I'd see the tone on the channel VU (let's say channel 4 in this case) when monitoring the sync head with the transport in stop mode. With the track in rec ready mode, as soon as I put the transport into record status the VU meters of the adjacent channels would show signal as well (channels 3 and 5 in this case), even if the adjacent channels had not signal physically connected!
Then I noticed this issue was present at 10kHz as well, but only with slight meter deflection on the adjacent channels.
What does this mean??
When I'd record the tone, the adjacent channel VU meters would show very unsteady levels, even when signal is already recorded on those adjacent tracks. On playback though, everything is totally fine...stable, isolated, etc. So the VU's are (fortunately) not showing what is being printed to tape, but I'm thinking this is going to need to be resolved before I take this thing into session.
How stable should I expect the meteres to be when monitoring playback? Between the repro and sync heads I've got some tracks that are rock steady at most frequencies, and some that are wavering a bit all the time at certain frequencies, and a few that are varying some (but less than a 0.5VU range) on for certain frequencies. Is this normal, or is it a sign that something is not right (i.e. should I expect all tracks to be rock steady over the test spectrum)?
I finally got a chance to look over your post and the videos (now that they’re all working
).
METER CROSSTALK ISSUE
Some interaction is to be expected while in sync mode at high frequencies and it only affects the adjacent meters, not what goes to tape. The higher the frequency, the greater the deflection at a given level. The phenomenon varies depending on the machine.
The first thing to keep in mind is this won’t cause any problems during real world recording… at least it shouldn’t if there’s nothing wrong with the machine. This is because when recording music the only thing that lives near 20kHz are upper harmonics and they are nowhere near what you’re hitting your meters with in your test.
A couple other tests you should try to confirm this:
1. Perform the same test with track 6, but also set record enable on tracks 5 & 7. Make sure you only have signal going to track-6 just like before. At 20kHz the deflection on the adjacent meters should be much less (maybe none at all).
2. Also do the same test with music from a CD or other source instead of a test tone. With music peaks around 0VU the adjacent meters should not be moving.
3. If you’re still seeing more interaction between the meters than you should, try connecting the outputs from your mixer to the corresponding inputs on the deck (except the input from the oscillator, of course), then perform the tests again. When you have the inputs (or outputs) disconnected (floating) it may allow spurious signals to affect neighboring components such as adjacent meter circuits. Even with all the faders down on your mixer the circuit for each channel is still complete and more resistant to interference.
Also keep in mind that recording a high frequency test tone while playing back another on an adjacent track has no real practical utility. You want to record each track and then play them back together (or one at a time) to get a picture of the machines frequency response. So while the meter interaction may be annoying it’s only a problem if it occurs while overdubbing during multitrack recording of music.
AMP CARD ISSUE
It’s usually the little things with the amp card. The contacts on both sides get oxidation buildup, bad capacitors and/or bad relays.
Sometimes DeoxIT isn’t enough, so try a fine brass wire brush (about the size of a large toothbrush) along with the DeoxIT. You can get them at hardware stores or in sporting goods departments that have gun cleaning supplies.
The relays on your amp card are the non-sealed type, so they will get oxidized. The clear plastic top lifts off so you can clean them with DeoxIT as well. It’s best to replace them with a sealed type, but cleaning them will give them some more life. When cleaning relays, apply DeoxIT and turn card upside-down right away, as these cleaners can damage some plastics.
The two electrolytic capacitors right next to the relay are more likely to fail than others, so you may fix your problem by changing only those.
One final note on the cards – a lot of manufacturers during 80’s and 90’s coated the solder side of circuit boards with a spray that was supposed to protect the traces and solder points from corrosion. Only trouble is this substance ended up breaking down over years and became conductive. It can cause all kinds of buggy ghost-in-the-machine behavior that will have you pulling your hair out.
I remove it with another gun cleaning product called Birchwood-Casey Gun Scrubber. Only try this if all else fails to fix the buggy amp card. You can usually detect this problem if the circuit board feels tacky or sticky to the touch.
You hold the circuit board in one hand so the edge faces the ground (wear rubber gloves) and spray the solvent onto the back (solder side) of the board until all of the sticky brownish residue has run off. Don’t spray it on the component side or get it in any pots or trimmers.
METER PLAYBACK STABILITY QUESTION
It’s normal for the meters to flutter a little, especially on edge tracks with high frequency tones. This is true whether recording tones with a blank tape or using a calibration tape by MRL, TEAC, or STL. You’ll see the needle move up and down… a half dB is typical, but it should be smooth, not jerky. In J. McKnight’s warranty for MRL tapes it states the amplitude must vary up and down by more than 1dB for the tape to be considered defective. It also depends on the condition of the machine.
A really important thing to understand is that tracks won’t necessarily behave exactly the same on the same head… there will be variation within manufacturer specs.
). Or if yer like me you'll find something will work...like a jeweler's screwdriver... 
