6k Programme bus L/R imbalance

[MartyAckerman]

Hi all, I'm back again with my slightly problematic board.

I've finished re-capping the entire 651v center section. I've also re-capped the 82E162 master audio card from the 688v section, which is specific to 6000 series baords. In addition, I replaced all of the 5534's on the 162 card except the two or three that are specific to the mono and slate signals.

I'm getting a consistent 11db difference between left and right from the program bus.  The A, B, and C buses all seem to be fine and equal on the left and right; it's only when the signal passes through the bus comp, monitor volume pot, and programme bus that there is an issue.

I made some measurements using pro tools with Izotope's Insight.  I know it's not lab equipment, but it demonstrates the issue at least. I'll put those below. I was sure the 162 card would have the issue, but apparently not. Can anyone give a suggestion as to where I should check next?

Measurements

-18dbfs 1khz sine wave from pro tools
patched into A, B or C buss insert inputs -  all the same.
programme out patched to multitrack send 3-4 (pro tools) in order to measure via Izotope Insight 2.

L: -27.2
R:-16.7

Same setup, but Mon Insert out patched to pro tools instead of programme out

L: -17.6
R: -17.5

8 track record A, B or C bus out patched to pro tools instead of programme out all within 1/10 db

L: -17.3
R: -17.4

ST Rec out while signal fed to A, B, or C bus insert in

L: -27.7
R: -16.7

[Chris Simon]

How about Oscillator to Program? If that's not balanced, suspect a fault on the '195 card. If it is balanced, work backwards to the L and R '026 cards. Try swapping those cards to see if the problem follows one of them.

[radardoug2]

I dont like to be rude but if you own a 6000, then you need basic faultfinding skills, and apply them.
Study the circuits carefully. Maybe make or use the block diagram. Insert tone at the front, and using a scope or millivoltmeter, follow the signal through the various cards until the level drops. Then you have found your problem. You need a full set of extender cards. Otherwise you will waste lots of time.
In my opinion, nothing beats having the right test gear, and these days some very good peices can be had off Ebay for not much money.

[MartyAckerman]

Thanks for the reply! I was actually typing this as you posted.  I've swapped the 26 cards and the problem did not follow them. Unfortunately the oscillator has never worked on my board.

I'm diving a little further into this and have some more info.  If it gives anyone an idea for what to try next, I'd be grateful to hear it.

Also, I'm fairly sure I found a small error in the service manual. The pinout on page 246 of the 6k service manual seems to have pins 3 and 4 reversed. My measurements and the schematic on page 251 seem to agree with me.

Manual here for convenience: https://www.dropbox.com/sh/nl9hb5276u1ha6m/AAAGGIokguPt1qS_Crg6Nj9-a/SL6000?dl=0&preview=SSL+6000V+edit.pdf&subfolder_nav_tracking=1

I'm able to see the issue on some of the card pinouts. I fed a -18dbfs sine into the programme bus inputs. Measured the pins to the 0v large trace on the main 651 motherboard.

After making and reviewing the measurements below, my suspicion is that the error must be within the 195 card. Does that make sense? It seems to get equal LR level in, but squirts out uneven levels. I don't have my head around the routing between cards and sections, so I may be wrong about that.

CF82E154 card:
Pin 1 Programme Meter input L - 0.22 Vrms
Pin 2 Programme Meter input R -  0.77 Vrms
Pin 3 (output to?)Control room level pot L: 0.22 Vrms
Pin 4 (output to?)Control room level pot R: 0.75
Pin 13 L Programme input - 0.22 Vrms
Pin 24 R Programme input - 0.68 Vrms

Next, I measured between two pairs of pins:
Pins 25 and 26 Left Monitor Input + and -: 0.68 Vrms
Pins 27 and 28 Right monitor Input + and -: 0.7 Vrms


Next was the 195 card.
CF82E195 card:
Pins 34 - 35 Monitor out L +/-: 1.25v
Pins 36 - 37 Monitor out R +/-:1.25v
Pins 40 - 41 Prog. Out R +/-:1.21v
Pins 32 - 33 Prog. Out L +/-:0.36v
Pin 53 Prog. L in:0.79v
Pin 50 Prog. R in:  0.79v
Pin 7 Prog. L Monitor Out: 0.34v
Pin 23 Prog. R Monitor Out: 0.81v
Pin 1 Prog. L Meter Out: 0.36v
Pin 2 Prog. R Meter Out:0.81v

[radardoug2]

The best way to do this is with extender cards and a scope. Then you can probe easily the output pins of the opamps. Follow the schematic through and check each opamp output. But it does look like the 195 card is faulty.

[Chris Simon]

 Doug's right; the best way to troubleshoot cards in the master section is with extender cards. In absence of those, your task is much more painful. Double check that capacitors C7-C10 are replaced properly. Throw some new 5534's in the T4, T5, and T6 positions. Now it gets ugly. Consider the schematic: the Programme L Input signal splits at J112 64L. The path to Monitor Out proceeds to it's balancing circuitry, and you know that's good, so therefore the signal at the split point is good. The Programme Out path proceeds through 64L to its balancing circuitry. Is 64L bad? Or is it good, and not being sent the right switching logic from the T22-Tr2 circuit? Notice J112 65L; it's function is to apply the Slate signal to Programme Out, which is why I suggested Oscillator to Programme as a test of the Programme Out.

 You see, there's a lot of potential faults. Extending the card so you can read voltages is critical. You've already established that right Programme Out is good, so it would be a trivial task to compare those voltages to the faulty Left side. Without the extender, you're stuck changing one component at a time, which is painful, but possible. Good luck.

[The-Greenhouse-NH]

In case you don't have any card extenders (like I didn't): the best method I found to get at the desired test points was to take some thin insulated wire, and temporarily solder it where I wanted to probe. Possibly even more handy for troubleshooting the 688 - though mine is on indefinite vacation now!

It's a little more annoying to diagnose JFET 64L since your oscillator doesn't work, but you should be able to patch into the return side of the Oscillator output with any old sound, which hooks you into the Slate and allows you to send signal directly into the 195. That would be the easiest way to diagnose if 64L is the reason for low level.

[MartyAckerman]

Oh wow, that's two great tips, thank you!

I do not have the extender for that card.  I've already replaced t1 - t6 and rechecked the caps. I've been recording for a couple days using "monitor from 8 track" to get the balanced LR, so I'll get back into it in a day or two.  In the meantime I've emailed Desk Doctor, hopefully they'll have a 195 card or extender available. If anyone knows where to find one, let me know.

[MartyAckerman]

I've replaced T4, 5, and 6, temporarily replaced T1 with an lm324 and also replaced FE1 and FE10, which I believe is labelled as 64L, the first J112. All to no effect.  I then soldered wire leads to pin 6 (output) of T4, 5, 6, 7, 8, and 9.

Am I correct in assuming the AC voltage between the programme out positive and negatives (pins 32 -33 and 40 - 41) should be equal if they are properly balanced? There are discrepancies between T5 and t8 as well as between T6 and t9. I'll double check C7 and C8, as well as the resistor off the output of T5. Running out of ideas after that.

Measuring pin 6 of  T4, 5, 6, 7, 8, 9:

T4: 0.73
T5: 0.428
T6: 0.741

T7: 0.68
T8: 1.0
T9:0.10

Pin 32 Prog L Out+: 0.41
Pin 33 Prog L Out-: 0.10

Pin 40 Prog R Out+: 1.06
Pin 41 Prog R Out-: 0.05

[Chris Simon]

It would appear the channels are roughly balanced at T4 and T7, and the problem on the Left side occurs after that. Out of curiosity, what happens to your readings if you deadpatch the Programme Insert returns? You'll want to measure between pins 32 and 33 for Left, and 40 and 41 for Right.

[MartyAckerman]

I've done that measurement as well and found no difference, though I wonder if I did this correctly.

I'm afraid I'm about to say something stupid, but here goes: When I deadpatch the insert returns of the Programme bus, I should be cutting off sound to the monitors, correct? I have "Programme from A+B+C" and "Monitor from programme" selected.  I'm injecting tone by sending a line out from pro tools and patching into the A bus. The signal responds to the main VCA fader and the bus compressor. When I deadpatch the programme bus insert return (patch cables with one end unplugged) into the bottom row of the programme insert, I still have the tone in the monitors.

not deadpatched
pins 32 - 33: 0.464v
pins 40-41: 1.18v

deadpatched Programme insert return
pins 32 - 33: 0.469v
pins 40-41: 1.18v


Since my last post I've done some additional measurements on T4, 5, 6, 7, 8, and 9.

Pin 2 Inverting input

a T4: .002 and lowers
b T5: 0.8
c T6: 0.8

a T7: .002 and lowers
b T8: .299
c T9: .299

Pin 3 Non-inverting input

a T4: .002 and lowers
b T5: 0.100
c T6: 0.074

a T7: .002 and lowers
b T8: .252
c T9: . 253

Also checked v+ on the above op amps and got 17.5 VDC on all.

[Chris Simon]

Deadpatching the Programme Out returns cuts the signal to the stereo distribution (Stereo 1-5 Rec outs). The Monitor Outs are picked off before this.

[MartyAckerman]

–SOLVED!–

Thank you all so much for your help with this. I learned a lot about putting theory into practice in troubleshooting these kind of issues. The fix is slightly uncertain.  I ended up replacing a few additional J112's, then resoldering/reflowing many of the resistors and sockets around T4,5, and 6. I then beeped out all of the connections and replaced C8 and C9 . My best guess is that one of the capacitors was making good contact on the bottom of the pcb, but not on the top trace. I may have damaged it in my initial recap.  I was very careful and particular in replacing them. It also could have been a cold joint somewhere - I was lifting resistors to measure them accurately, so there were a lot of solder touch-ups.

In doing this detailed look at the board, I noticed some corroded leads on the bc212lb's. Although they're working now, it looks like they'd be nearly impossible to replace. Can anyone recommend a source or replacement for these?

[horizonsound]

Hi Marty,

BC212B will be the closest, but you need to rotate it 120° to get the correct pinout to line up with the board.

Anthony.