rob aylestone
Moderator
Yup! Dry joints!
Troubleshooting Hudson CS604 DO 70's analog mixer
- Thread starter bleachboy
- Start date
sweetbeats
Reel deep thoughts...
Yeah as soon as I saw the pics…I’d be reflowing all those solder joints with the buss wires that span across the cards. That’s a bad design. Bad for reliability because any time the console moves, depending on how rigid the chassis is, it will put strain on all of those joints. They are bound to crack eventually. And additionally, as you have discovered, it’s a ginormous PITA if ever you need to service something. Wow. If I loved the console and was going to keep it I’d be modifying it so at the very least they weren’t strapped with solid core wire, and replace with stranded wire, or ideally come up with some connectorized solution, even if it was mounting solder pins to the boards and making individual wires that can plug in to each point. So that may be at least part of the problems you’re having. I would seriously reflow every single one of those solder joints so you can stop chasing your tail on that. And then see what you are left with. I’m still suspicious of maybe something else going on because none of the mix busses or your post-fade AUX busses are getting signal. But I’d start by reflowing those solder joints and see what you have.
sweetbeats
Reel deep thoughts...
Also, when you said you could get signal at the ECHO out but not the FOLDBACK out, can you clarify how you had the source switched? It looks like both pairs of those busses are switchable pre or post fader yes? The ECHO busses source either the LINE input jack, like, right after the input coupling cap C4, or post channel fader, and the FOLDBACK busses source either post EQ pre channel fader, or post channel fader. Clarify this because it is important to the troubleshooting.
Notice IC3 has the big task of driving all 4 mix busses, the direct out, and all 4 AUX busses when switched to post fade mode. That’s a lot for a humble u709. If none of that is working (when the AUX busses are switched to post fade mode), then I would check and make sure IC3 has power…and you said you swapped opamps. Tell us about that. Did you put in sockets? Trying to desolder/solder opamps would be hard with those cards installed. So how well do you trust your solder job with that?
Notice IC3 has the big task of driving all 4 mix busses, the direct out, and all 4 AUX busses when switched to post fade mode. That’s a lot for a humble u709. If none of that is working (when the AUX busses are switched to post fade mode), then I would check and make sure IC3 has power…and you said you swapped opamps. Tell us about that. Did you put in sockets? Trying to desolder/solder opamps would be hard with those cards installed. So how well do you trust your solder job with that?
Last edited:
This was actually the first thought that went into my mind as I woke up this morning. For all of my testing, the console has to be set up in the normal way so that I can access the jacks on the back of it to send and recieve signal to and from it, but in order to actually work on the channels, I’ve had to tilt the console 90 degrees on the backside (where the jacks normally are). I’ve had to do that multiple times so I’m sure this must have put too much strain on those buss wires. I will definitely reflow all of these joints and see what I’m getting. I doubt it’ll solve channel 13 but the monitor section of the console is giving me trouble also, I‘m pretty sure it could be those hard wired busses again.
I’m getting a heatlhy signal out of the ECHO & FOLDBACK busses, on the DIRECT OUT also, now that I’ve wiggled the channel card as per the video link I’ve sent in my previous post.
The PRE-POST fader switch is called MONITOR (pre) / MIX (post). However the fader themselves don’t seem to have any effect on the FOLDBACK jack no matter the setting on the switch, I guess the FOLDBACKS are pre-fader by default, and the switch only seems to be sending the FOLDBACK pre or post EQ. When the EQ is engaged, the MONITOR setting bypasses the EQ, so I’m guessing the MIX setting must be post EQ, pre fader. However the pre-post switch does seem to function normally with the ECHO SEND. When MIX is engaged, both the EQ and the fader have an effect on the signal. It’s a bit quirky innit ? But the console seems to be wired this way, I’m having the same results on all the channels.
As far as the OP AMPS go, the channel cards all have sockets to put them in or out (Thank god), so I have done absolutely no soldering on those, just dropped the new ones in place of the old ones.
I’m getting a heatlhy signal out of the ECHO & FOLDBACK busses, on the DIRECT OUT also, now that I’ve wiggled the channel card as per the video link I’ve sent in my previous post.
The PRE-POST fader switch is called MONITOR (pre) / MIX (post). However the fader themselves don’t seem to have any effect on the FOLDBACK jack no matter the setting on the switch, I guess the FOLDBACKS are pre-fader by default, and the switch only seems to be sending the FOLDBACK pre or post EQ. When the EQ is engaged, the MONITOR setting bypasses the EQ, so I’m guessing the MIX setting must be post EQ, pre fader. However the pre-post switch does seem to function normally with the ECHO SEND. When MIX is engaged, both the EQ and the fader have an effect on the signal. It’s a bit quirky innit ? But the console seems to be wired this way, I’m having the same results on all the channels.
As far as the OP AMPS go, the channel cards all have sockets to put them in or out (Thank god), so I have done absolutely no soldering on those, just dropped the new ones in place of the old ones.
sweetbeats
Reel deep thoughts...
I looked at the schematic too quickly. Here is what it says about how the FOLDBACK and ECHO busses should work in their various source settings:
FOLDBACK - MONITOR: sources LINE input pre EQ pre channel fader
FOLDBACK - MIX: sources channel input post EQ pre channel fader
ECHO - MONITOR: sources LINE input pre EQ pre channel fader
ECHO - MIX: sources channel input post EQ post fader
Can you confirm the above, each detail, is how your console channels’ auxiliary busses function? AND confirm they work in all modes on channel 7
Okay on sockets…are you sure you didn’t bend a pin putting IC3 in on channel 7? Also, there are good quality sockets and not as good quality sockets. You said you swapped the stock u709 back in and it still didn’t work. Maybe you do have a bad solder joint or bad contacts on the socket. But I also want to know what opamps are you swapping in?
FOLDBACK - MONITOR: sources LINE input pre EQ pre channel fader
FOLDBACK - MIX: sources channel input post EQ pre channel fader
ECHO - MONITOR: sources LINE input pre EQ pre channel fader
ECHO - MIX: sources channel input post EQ post fader
Can you confirm the above, each detail, is how your console channels’ auxiliary busses function? AND confirm they work in all modes on channel 7
Okay on sockets…are you sure you didn’t bend a pin putting IC3 in on channel 7? Also, there are good quality sockets and not as good quality sockets. You said you swapped the stock u709 back in and it still didn’t work. Maybe you do have a bad solder joint or bad contacts on the socket. But I also want to know what opamps are you swapping in?
Yep, all of the above settings work as they should on channel 7, that is only after gently moving the card back and forth until I’m getting output, as per my video. Basically the channel itself seems to be working fine, but there must be a shorting of the connection or dry joint somewhere that I just can’t locate. Between the channel card and the way it’s wired to the outputs, I guess. I don’t think it’s coming from any part on the channel. The IC pins have not been bent. I’ve swapped the u709 on channel 7 with the u709 on channel 8, I’ve also tried putting a new T.I 741 in place of the 709, which did not make any difference whatsoever.
sweetbeats
Reel deep thoughts...
So at this point if you’ve re-flowed solder joints with the buss wires (the ones that go channel to channel), and every other channel is passing signal to the mix busses fine, it’s most likely something on the channel 7 PCB.
I’m going to say again you should stop swapping/shotgunning/stabbing in the dark. You’ll save yourself time and minimize the potential for additional complicating damage. For example you can swap opamps all day long, but if you look at the schematic you’ll see that if you can get signal at the direct out, echo and foldback outputs from channel 7 (the latter two when sourced to the MIX), what opamp is driving those outputs? IC3. That tells you what? It’s working. Do what you can from the console’s own feature set to narrow down the issue first. Even if you can’t read a block diagram you can test all the functions and features and document what doesn’t work right and THEN begin to investigate further/take action.
The next thing I would do is inject 1K tone and if I didn’t have a scope, which as rob mentioned really is invaluable once you are at this point, I’d take my DMM with frequency counter mode or a dedicated frequency counter if my DMM didn’t have that function, and start tracing from the buss assign switches upstream. I’m assuming it is upstream of the assign switches because you are getting nothing to any of the mix busses. Look for 1K tone and where you pick it up, you are just upstream of the fault.
[EDIT]
Also, yes u741 is pin-compatible with u709, but there are external tuning components that can be utilized with these opamps, and you’ll see IC3 has some parts installed for this purpose (C18, C19, R45), and it is possible those components or component values would change with a u741 installed at IC3. The u741 doesn’t have all the same facets for this as the u709. So the u741 likely works at IC3, but may not perform optimally or correctly.
[EDIT AGAIN] Also, it is possible a u741 doesn’t have the same drive as the u709 which is why they used the u709 at IC3 with the potential to drive 9 outputs. I can’t tell from the datasheets because neither the u709 or u741 are specifically designed for audio, so the specs don’t include certain data like output drive potential. But the 741 is a higher spec part, so the only reason I can think of why they would use a 709 instead is because it has better drive than the 741.
I’m going to say again you should stop swapping/shotgunning/stabbing in the dark. You’ll save yourself time and minimize the potential for additional complicating damage. For example you can swap opamps all day long, but if you look at the schematic you’ll see that if you can get signal at the direct out, echo and foldback outputs from channel 7 (the latter two when sourced to the MIX), what opamp is driving those outputs? IC3. That tells you what? It’s working. Do what you can from the console’s own feature set to narrow down the issue first. Even if you can’t read a block diagram you can test all the functions and features and document what doesn’t work right and THEN begin to investigate further/take action.
The next thing I would do is inject 1K tone and if I didn’t have a scope, which as rob mentioned really is invaluable once you are at this point, I’d take my DMM with frequency counter mode or a dedicated frequency counter if my DMM didn’t have that function, and start tracing from the buss assign switches upstream. I’m assuming it is upstream of the assign switches because you are getting nothing to any of the mix busses. Look for 1K tone and where you pick it up, you are just upstream of the fault.
[EDIT]
Also, yes u741 is pin-compatible with u709, but there are external tuning components that can be utilized with these opamps, and you’ll see IC3 has some parts installed for this purpose (C18, C19, R45), and it is possible those components or component values would change with a u741 installed at IC3. The u741 doesn’t have all the same facets for this as the u709. So the u741 likely works at IC3, but may not perform optimally or correctly.
[EDIT AGAIN] Also, it is possible a u741 doesn’t have the same drive as the u709 which is why they used the u709 at IC3 with the potential to drive 9 outputs. I can’t tell from the datasheets because neither the u709 or u741 are specifically designed for audio, so the specs don’t include certain data like output drive potential. But the 741 is a higher spec part, so the only reason I can think of why they would use a 709 instead is because it has better drive than the 741.
Last edited:
sweetbeats
Reel deep thoughts...
Can you post some pics of the console overall? Control surface and backplane?
What this console does have going for it is some usable inline monitoring functionality and the PCBs are high quality glass fiber…vintage large traces…much more durable and serviceable…and the jacks are actually mounted to a backplane, not PCB-mounted. And the audio power rails are +/-17V for higher than average headroom potential.
What is not so good is the aforementioned buss wiring with the solid core rods strapped across the boards…super bad idea IMO, but that can be rectified. The other thing that’s cool is the single opamp packaging onboard with the 741 and 709 opamps. If you’re happy with the sound then stay with it, but, and I am *really* not one to berate opamps, the 741 and 709, though they served their purpose well at the time, and do have the capability as mentioned earlier to be externally “tuned”, are really, really not desirable opamps for some decades now. Like…not. But the circuit design is ripe for using the 5534 (or other opamps) in place of the 741s and 709s but I mention the 5533 because it is still respected, cheap, readily available, I think a great sounding audio opamp, and would “drop in” but would require tech time to tune the chip to the circuits and therefore possible replacement and/or removal of some of those surrounding components (C18, C19, R45). The 5534 would be a vast improvement while remaining “vintage.” And the 4558, same thing…oddly revered still in some circles, but even the very cheap and readily available TL072 would be an improvement, less noise and distortion, better slew rate, reliable…100% drop-in…lots of other options too but I’m mentioning those that are reliable, cheap, and not outside the nature of the console.
Anyway these were some thoughts bubbling around in my head and they had to get out because I don’t have room for them.
What this console does have going for it is some usable inline monitoring functionality and the PCBs are high quality glass fiber…vintage large traces…much more durable and serviceable…and the jacks are actually mounted to a backplane, not PCB-mounted. And the audio power rails are +/-17V for higher than average headroom potential.
What is not so good is the aforementioned buss wiring with the solid core rods strapped across the boards…super bad idea IMO, but that can be rectified. The other thing that’s cool is the single opamp packaging onboard with the 741 and 709 opamps. If you’re happy with the sound then stay with it, but, and I am *really* not one to berate opamps, the 741 and 709, though they served their purpose well at the time, and do have the capability as mentioned earlier to be externally “tuned”, are really, really not desirable opamps for some decades now. Like…not. But the circuit design is ripe for using the 5534 (or other opamps) in place of the 741s and 709s but I mention the 5533 because it is still respected, cheap, readily available, I think a great sounding audio opamp, and would “drop in” but would require tech time to tune the chip to the circuits and therefore possible replacement and/or removal of some of those surrounding components (C18, C19, R45). The 5534 would be a vast improvement while remaining “vintage.” And the 4558, same thing…oddly revered still in some circles, but even the very cheap and readily available TL072 would be an improvement, less noise and distortion, better slew rate, reliable…100% drop-in…lots of other options too but I’m mentioning those that are reliable, cheap, and not outside the nature of the console.
Anyway these were some thoughts bubbling around in my head and they had to get out because I don’t have room for them.
sweetbeats
Reel deep thoughts...
No, don’t just give the opamp a a try. Love with the stock configuration first and determine if there are limitations you can reasonably deduce would be resolve with a change. That is the only reason to change opamps. You have to be skilled with an oscilloscope to “tune” the 741 and 709 replacements. Do not just throw parts at it. That’s how you get into trouble. If you decide you want to mess with that you find yourself an experienced tech or you learn how to do it yourself and obtain the proper gear to do it.
Last edited:
Yes of course. My main and only goal here is to try and make that console work properly to record and mix/sum with it. I’m in love with the way the preamp and EQ sounds. It’s way less practical than the M512 I’m using now as far as routing/busses/no phantom power/no polarity switch…but still. Sounds great. I have yet to try and make the limiters work though, but I don’t think they’re anything special. Still it would be great to have them work as they should, to compress room mics or whatnot.
So far I need to :
- locate the exact position where the short is on channel 7 occurs and fix it.
- find out why channel 13 has so much more gain/output than all the other channels.
- I have no signal at the monitor section (headphones etc), I can only monitor the solo buss from there, not the multitrack or busses.
- when the limiter is inserted to a channel, all I have is a distorted sound, that is lower in volume than when the limiter is not plugged in the insert jack.
Lots of work to do there…
So far I need to :
- locate the exact position where the short is on channel 7 occurs and fix it.
- find out why channel 13 has so much more gain/output than all the other channels.
- I have no signal at the monitor section (headphones etc), I can only monitor the solo buss from there, not the multitrack or busses.
- when the limiter is inserted to a channel, all I have is a distorted sound, that is lower in volume than when the limiter is not plugged in the insert jack.
Lots of work to do there…
Attachments
sweetbeats
Reel deep thoughts...
Thanks for the pics of sections of the backplane and control surface. If you have a chance can you capture images of the whole thing though, not just sections. And I’m talking about the frame assembly with the PCBs in it…the whole thing from different angles. You don’t have to do this if you don’t have time but the zoomed in partial pics of things is driving me nuts. It’s helpful to have a picture of the whole thing and I can zoom what I need rather than an image out of context and I’m not sure where that section sits, etc. It’s like you asking for a picture of my dog and I send this:
When you reflowed buss wire solder joints did you do all of them or just the ones relative to channel 7? If the latter, you should do every single one but only after the cards are re-mounted to the dress panel. There’s no point doing any of that now since the cards can move around a bit.
When you reflowed buss wire solder joints did you do all of them or just the ones relative to channel 7? If the latter, you should do every single one but only after the cards are re-mounted to the dress panel. There’s no point doing any of that now since the cards can move around a bit.
