Troubleshooting 414 mkii playback issue

[Nolan]

I just got a 414 and I am trying to diagnose an issue. I have found that all the functions work as expected, but when I attempt to play a tape back with the volume cranked, I can just hear a very faint crackle as if the audio is attempting to play back both through the headphone jack and RCA outputs. The record function works as I was able to record and play the tape on another device. All the lights and VU meters indicate that there is audio on the tape attempting to playback. Also the microphone is audible through the monitor, just nothing playing back from the tape. I read that there may need to be some capacitors replaced. Any idea which ones I should replace Or maybe something else going on? I opened everything up and it looks to be in pretty good condition. Any insight will be helpful, thanks!

 

[SkywaveTDR]

Looking around in a unit does little good. In fact it is a waste of time to open one up unless you have the means to fix something like this. If a tape play problem is there I put a 1KHz 0 Vu sine wave tape I made and let it play. If more than one channel is out at one time this would indicate a power supply issue or mute system is on. Mute system are transistors that short a signal to ground when the deck is to have no output. You did clean the head right? There is no common type problem that everyone is looking for to solve their problems- Electronics is not that way.
The crackling of audio may mean there is no DC power to a head amplifier section.
To say exactly what the problem is I would have to see the machine and I don't need anymore here.

 

[Nolan]

Thanks for the response @SkywaveTDR! I think you may be correct that there is something off about the power supply. I have a power supply lying around that I used that is the same output, but I am thinking that I need to order a new one since I read that these devices have a reverse polarity in the power adapter. I also noticed that the largest capacitor (not sure if that is the correct term, i'm a bit of a novice) nearest to the power jack inside the device looks a bit leaky. I did clean the heads to the best of my ability and the transport mechanics all seem to be in good working order. I think a good start may be to order a new power supply and replace that capacitor. What do you think? I will be sure to post updates as I address them. Thanks again!

 

[SkywaveTDR]

If you plug in a reverse power supply int these I don't know if there is any protection and if reverse you could be blowing out all kinds of stuff. Op amps do not like reverse voltage at all and they will all be ruined. When you say a like voltage did you look at the polarity as well?

 

[Nolan]

Hello again @SkywaveTDR, thanks for following up. After reading your message, I am worried that I fried the thing. Here's a picture of the power supply I used. I just. ordered a replacement for the 414 power supply and I am hoping that the voltage / amperage is low enough on the power supply I've been using to have not caused too much damage. All the lights and other functions still work, so I'm crossing my fingers. If that doesn't do the trick, then I'll get the soldering iron out and try to replace that capacitor and check all the other connections while I'm in there. Thanks again!

https://drive.google.com/file/d/1qj9rLeyQNN45wJhwGd3OXUcuf3nqIM0u/view

 

[Nolan]

Hey again @SkywaveTDR ,

I finally got around to opening the thing up and here's what I found. One of the corners has broken off which looks like contains several electrical paths and the largest capacitor near the power supply appears to be a bit leaky. I assume these are likely the source of the issue. From your experience, does it sound like I'm on the right track? I am not sure how I would go about repairing that broken corner to ensure that all the connections are working properly, but I may try to glue it with some solder and hope for the best. Any further insight would be greatly appreciated. Thanks!

 

[SkywaveTDR]

The caps do not leak it is most likely glue you will find in every one of those. Bad caps either show as shorted or open by meters and this is too new a product to have that at this point.
The broken corner? Of course that is the problem. Put it back to the corner and use epoxy to glue it from the top as well as broken edge to secure it. You are just putting it back for peace of mind or board stability. Then take a razor blade and at each end of the board get about 1/4" of the green enamel off- not on the broken piece but the parts that it came from and is going to. Then I would use magnifiers that I wear and solder a telco wire from source and then bend it over the glued board to the destination solder position. When getting off the green enamel when soldering to it use a little heat as possible so as not to damage the trace. I use a 40 watt Weller but the tip I use transfers much less heat at that point- it is the very pointed tip. Anyway use of some solder flux might help in bonding the wires. Make sure none of then are touching each other. When all traces are patched you can do continuity tests with a DVM meter and make sure the are all conducting and also not touching each other. You don't have to but some guys put a strip of hot glue across the wires to hold them. The way I do it they are bent to conform to the traces on the broken off piece and will look neat that way. If you do not feel you can do this then hand it over to a technical type that can but the unit can be fixed. This would be considered an easy repair except for the work involved as this is most likely the problem- there can be other cracks if this was cracked as well.
If you are in my area and have the board out I can do the job.

 

[Nolan]

Thank you so much @SkywaveTDR! I was able to solder some new wire over the broken traces to repair the issue! I epoxied the corner back on and then soldered some wire past the cracked corner and got it up and running again! there are still some crackle issues that I am hearing a bit, but at least I can hear the recorded audio now. I am stoked to have the thing up and running. Thanks again for all your insight!!