Mackie 1400 Hot Light and going quiet

[NBD925]

I also just found the Service Manual.

https://elektrotanya.com/cgi-bin/download2.cgi?dk=bsntp1qhcf41gr0gdea2ttja6v2qnw76cmn4qw4 hpf0ubqji&fid=136763&file=mackie_m-1200_1400_1400i_sm.pdf

[Pixel]

Ideally you start with the correct schematic and the ability to understand some of what is going on in the circuit. I would literally take a magnifying glass and look at every component and connection to see if you notice anything that looks suspect.

It would be helpful to know what your level of experience with repair is and what tools you have available to you.

You are kind of getting in your own way in this thread. So much random information. If you want some help you need to verify that you have the right schematic and then post it along with all the symptoms from YOUR amp. It might be best to post that you are abandoning this thread and starting a new uncluttered one.

[NBD925]

I don’t understand what you mean Pixel. These schematics and manuals are for my Mackie 1400 and I have described what some of my problems are. As I research the solutions and materials to get the answers, I have posted my findings here. I am also posting them here so others following along might benefit from the links to those materials. Another individual asked that I post some pictures of the small board and any schematics.

Just doing my best here to help others more talented than myself with electronics possibly diagnose what may be going on with this hot light issue. The Service Manual has prompted me to build new ribbon cables for this amp based on serial number range.

Bought the supplies at Digikey.

[x-pro]

What's the point of message. #17?
Your message #1 indicates the position designations of the elements that are given in the schematic in the topic in message #4.
The fact that some elements of the schematic do not correspond to the location on the circuit boards is not a problem. If the schematic generally matches, that's enough to fix the problem.
You may have a different version of the PCB layout of that part of the circuit.
There is a possibility that the amplifier model is different as well. You did not accurately specify the model of the product here.
I searched the internet for Mackie models for the 1400 model from the title of your thread.
The Internet only gives the model - M1400, M1400i.
Please specify the exact model of your amplifier.
The manual in post #16 you refer to repeats #4.
The schematic in the link in message #15 does not fit at all. There are no elements with the positions in message #1.
Troubleshooting on third-party resources is commendable. I do not exclude that what is described there is the same author on different forums. But, earlier it was correctly pointed out that these are not necessarily the same defective parts. Especially without analysis and measurements.
I in post. #3 pointed out some questions to move forward in the search for the fault. But, no answers from you.
And, we are waiting....

[NBD925]

Mackie Series FR
Model M-1400
Serial Number: AH15857

Issues: Both of these issues are common to the Mackie M-1400 FR series.

The Hot light randomly comes on even though the amp is not hot. It will remain lit. It seems to effect channel 1. The amp seems to go quiet or reduce output and then randomly come back to full output.

Solutions:
The ribbon cables are a known source of problem with these Mackie Amps. I have looked up my serial number and this falls into the serial number range with a recall or updated part. I have ordered new parts from Digikey to replace the two ribbon cables (4.25 inch and 18 inch referenced in the Service Manual) The IDC headers will need to be replaced so I purchased them as well. See part numbers below.

3365/20 300SF MC20G-5-ND CBL RIBN 20COND 0.05 GRAY 5' Available Quantity Backorder Quantity Unit Price Extended Price 1 0 7.86000 $7.86

M50-3301042 952-2562-ND CONN RCPT 20POS IDC 30AWG GOLD Available Quantity Backorder Quantity Unit Price Extended Price 4 0 3.67000 $14.68

3220-20-0100-00 1175-1636-ND CONN HEADER VERT 20POS 1.27MM Available Quantity Backorder Quantity Unit Price Extended Price 6 0 1.08000 $6.48

I hope, I got the right stuff. I did my best to get the correct pin spacing and type. Hope the headers work.

As for fixing the Hot Light being on:
I gathered as much info as I could about past known problems with this amp and it pointed to these potential components.
LM35 Temp Sensor
Q91 Q89 (Legs should be 1.Base 2.Collector 3.Emitter)
Resistors R205 and R137

I tested each of these components but only tested them while they were soldered into the board. (Not removed) just looking for major value discrepancies or opens. Noted resistor R-205 Showed a value of 21.8k and the color band on the resistor showed it should be 36,000 ohm +/- 5%

Like it or not, this is where I am at. I apologize for not getting a complete model number right off the bat. As for experience, I am not an electronic industry professional and have just some basic knowledge from Aircraft Maintenance A&P and diy projects at home.

I clicked the link for the Service manual and it seemed to be broken. I tried to attach a pdf of the service manual below hope that works.

[g1]

Both of these issues are common to the Mackie M-1400 FR series.

The Hot light randomly comes on even though the amp is not hot. It will remain lit. It seems to effect channel 1. The amp seems to go quiet or reduce output and then randomly come back to full output.

These must be 2 separate issues. The hot light circuit can not create any channel specific problems. If the hot circuit is activated, it will mute both channels.
So either you just have a 'nuisance' fault with just the light itself, or the circuit has been bypassed by someone.

The intermittent low output of channel 1 is independent of whether the light is on or off, correct?

[x-pro]

... the hot light stays on.

Okay.
What are the voltages on pins 6, 7, 1 of U5A with this indication?
Is the +16V and -16V supply stable?
And does it reach the pins U1?
Measurements should be made relative to the housing.

[NBD925]

Update on where Im at.

As I understand it, the ribbon cable should fix a few issues. The amp is disassembled for that ribbon cable and header fix right now so hot testing can not be done yet. Once I get and install those parts, I will complete the testing you guys have suggested.

The hot light being on did mute both channels, I believe. Then the amp would magically come back to full volume and work fine. It was random.

Im really stretching my memory here on the original problems but would it be possible for that hot light to be lit even with power off to the amp for some time. Maybe while a CAP drained or something. Ill try to ask my buddy more about some of the problems because he used this amp more toward the end.

Im sorry, I cant get those numbers to you guys right now. I dissembled the amp to get at the headers and solder joints. I hope its not more that a week or so.

One thing I would like to know is about safety. I have really been treading lightly working around the CAPS. What are my concerns with safety while working on this amp unplugged and on the bench? What are some precautions professionals use to work safely?

How does that safety change while testing components when plugged in for the above mentioned tests and getting the numbers you guys need?? Or are you testing these components in some other way like back feed with a probe?

[NBD925]

Anyone have any info on the safety questions above??

[The Dude]

Make sure caps are discharged before working on the unit- not only for your safety, but also so not to damage anything else in the circuit. You can measure the voltage across the caps to see if they are discharged. Voltage measurements must obviously be made with the unit powered up. The best advice is to make sure your probe doesn't slip and short anything. I haven't worked on one of these for quite some time, but used to work at a service center that was Mackie authorized. I can tell you that most of the problems with these amps were repaired by installing new ribbon cables. It's highly likely you won't need further repairs after replacing them.

[g1]

When checking voltages with the unit powered up, it is best to clip the meter's black probe to ground or chassis, then use only one hand to probe with the red. Usually they say to keep your free hand behind your back. That isn't absolutely necessary but you don't want to be touching the chassis or other things with it.

[NBD925]

Thanks for the safety tips. I will make sure to take precautions and discharge the CAPS and keep one hand behind my back. It sounds dumb but makes sense for a noob like myself for safety, especially when powered up.

I have been shocked before in a big CD player and it was enough to make me remember.

My Digikey order showed up and the headers and IDC connectors were wrong. The 3M ribbon cable was correct and looks good. The headers were of the wrong spacing. I needed .05 and I got 1.27mm. The parts were about half the size I needed. Im not sure how I messed that up but when your learning it happens. I contacted Digikey and they helped me locate the correct parts. Those numbers are listed below:

Header: 732-2096-ND
Cable Rectangular Receptacle Connector : 732-2104-ND

I purchased a YIHUA 929D-V Electric Desoldering Soldering Iron Solder Sucker

I also purchased: Some Cemtronics 80-3-5 Solder Braid to suck the leftover solder out of the holes. Thats just to make a clean work surface for the new headers.

I used the Yihua Solder Sucker to desolder the 4 headers on each board. It worked amazing! I am now ready for the new headers to arrive. Will be looking up a few videos on soldering technique just to get back in the swing of things.

In anticipation, I ordered some Kester 186 solder flux and some denatured Alcohol for Flux clean-up.

What would the best solder be for this application and the use of my new flux??? Is there a certain tip size anyone can recommend for these types of jobs??? I have a Weller WP-35 soldering Iron.