oooops.. what have I done to my 388?!

[mr.blisset]

So I was mixing the other night and I blew the F5 fuse while the machine was rewinding. I was working on a song at the very start of the reel. I've noticed it struggles to get up to speed recently when at the start of a reel and so I was helping it out by pulling down on the left control arm. I've been mixing a bunch recently and had no problems when not at the very start of a reel.

When I blew the fuse it was rewinding at the time and I assumed it happened as I was running an oil heater off the same power board. I figured the heater must have switched on and spiked the power to cause the 388 to blow the fuse. The little green lights came on when I press the various transport functions but the solenoids didn't engage and the tape wouldn't move. No sound...no function at all when pressing different transport functions.

So today I put a new F5 (3A slowblow) in the 388. Everything is running great again. I put a new reel on and when to track a metronome and keyboard outline of a new song.
I started off at the very start of the reel (thinking this was a mistake now?) Pressed record and did my take. When I finished I walked over to the machine and noticed it had stopped at 2.35mins in. The play button light was still on but nothing was moving and there were no mechanical sounds.
I noticed the all to familiar smell of something being cooked inside the machine. oh no.

Opened it up and noticed the fuse was still intact, slightly darkened where the white part usually is on a slowblow fuse... but still intact.
The bias PCB cards were quite warm and when I stuck my nose in there the power supply and fuse section to the left didn't give off a smell but just to the right where the bias PCB cards are there was an obvious smell of cooked something.
I pulled both cards. The bias PCB closest to the power supper has noticeable blackening around the solder joints of W124 and W123. There are no components here, just a bridging wire.
All the pods are scorched with the exception of the W123 pod that goes to W104 on the PCB.
The other three look slightly toasted but the pod on W124 that goes to W103 looks particularly scorched compared to the other three.

The other bias PCB looks okay in comparison but the same pods do look like the got a bit warm. No darkened burnt looking stuff though.

I hoping someone here might know what has happened? I guessing I've made the machine work too hard due to the tension arms coming slightly out of alignment over time. I wish I could replace a component at W123 and W124 but there's nothing there, its just a bridging wire. So if I've toasted something it's further up right? If anyone has any idea of what other PCBs to scan for damage that would be a big help too.

I'm going to go buy another fuse tomorrow and am really hoping it comes back to life again. The fuse does seem to be intact so I'm not sure this will help.

Thanks

 

[sweetbeats]

Was the original fuse at F5 a slow-blow fuse?

Regarding W123 and W124 on the BIAS PCB, unfortunately the schematics don't show the jumper wires, and the PCB layouts are too hard to read in my copy of the 388 service manual, so you'll need to put up some high quality pics of the trace and component sides of the card so I can identify what power rail is being over-drawn. Something downstream of those jumpers is drawing too much current, and those jumpers are a point of resistance and are heating up. But I can't tell what is upstream or downstream of those jumpers.

This is one of the reasons the 388 can be a PITA to troubleshoot, because circuits meander a bit on that machine. There's a lot of stuff happening in a 388.

 

[mr.blisset]

Hi sweetbeats! thanks for the response. Hopefully my issue is as easy as the last one you helped out with . I do have some good news however.

firstly, to answer your question, yes the original was a 3A slowblow.

luckily, I have a put another fuse in and I have all the transport functions going again. phew. the last fuse that did in fact blow looked fine, so you can imagine how relieved I am. Still a little concerned about how hot things got in there though.

Would you say that the left tension controller arm needs further adjustment (I have to pull it down ever so slightly to help it rewind when working on the first few mins of a reel) so that everything is running smoothly and not straining things in terms of the power-rails? I've been mixing a 6 track e.p recently and everything was going better than fine, up until I was mixing a take that began at the VERY start of a reel. Then I started running into these problems. This is surely no coincidence?

I wont touch anything until you give the go ahead on this in case there is something else going on (ill put through those BIAS PCB pics in the next msg from my smartphone). If it's the tension that needs adjusting, then according to the manual I have to adjust the R112 control. Given how I only need to place the tiniest bit of pressure downwards on the left arm to help it out, I am very wary of making things worse. I am wondering how much of a turn will make a difference here? Should I turn a 1/4 at a time clockwise to lower the arm? Is it visually obvious with what is happening in regards to the tension arms when adjusting? I don't have the recommended tool to measure the tension so im not sure how sensitive the adjustments need to be.

Also I'm thinking about doing some preventative measures in terms of recapping etc. Do you think it could be of benefit for 388 owner on this forum to start a new thread discussing options for replacing power supply caps etc.
Also would love to hear your thoughts on the 388's weak points. Assuming everything is running well, what might break first from general wear and tear kind of thing. I have already put a new capstan belt on my machine and also have a spare. I think I'd like to start building up my spares stock so if this machine goes down I can repair it quickly so i can get back to using it! Is doing something like this possible?

EDIT: so I can't upload the PCB pictures from my phone. Also my computer is conveniently not letting me put them onto my computer. Would you still like PCB pics or is this a tension issue? Thanks

 

[sweetbeats]

Would you say that the left tension controller arm needs further adjustment (I have to pull it down ever so slightly to help it rewind when working on the first few mins of a reel) so that everything is running smoothly and not straining things in terms of the power-rails? I've been mixing a 6 track e.p recently and everything was going better than fine, up until I was mixing a take that began at the VERY start of a reel. Then I started running into these problems. This is surely no coincidence?

So...Neither you nor I have any idea if it is or is not a coincidence, and I'm not going to waste your time or mine conjecturing.

What kind of tape are you using?

Do you have the service manual? If so it tells you how to assess if the tension arm positions are correct and how to adjust the tension arm positions if they are incorrect.

I can't say if yours need adjusting or not because I can't see what the machine is doing. But you can, and if you have the manual the instructions are in there.

But before any of that, what kind of tape are you using?

If it's the tension that needs adjusting, then according to the manual I have to adjust the R112 control. Given how I only need to place the tiniest bit of pressure downwards on the left arm to help it out, I am very wary of making things worse. I am wondering how much of a turn will make a difference here? Should I turn a 1/4 at a time clockwise to lower the arm? Is it visually obvious with what is happening in regards to the tension arms when adjusting? I don't have the recommended tool to measure the tension so im not sure how sensitive the adjustments need to be.

Again, do you have the manual? You don't need a Tentelometer to do the tension arm position adjustment you are talking about adjusting R112 on the Reel Servo PCB. It's a visual adjustment. All the instructions are in the service manual.

so I can't upload the PCB pictures from my phone. Also my computer is conveniently not letting me put them onto my computer. Would you still like PCB pics or is this a tension issue? Thanks

There is no way to know if your fuse/overheated circuitry issue and your tension arm positioning issue are at all related. Assume they are unrelated until you can prove otherwise. I don't need to see the pics unless you want me to see them. But I can't assist any further with any determination of which power rail is being overdrawn without additional info.

 

[mr.blisset]

Yeah okay I hear you. I'll managed to get these pics into my computer via drop box.

I'm using Maxell 35-90

My mistake on thinking I couldn't do it visually. I see the tentelo meter is for measuring back tension.

I've tried to get them to where they need to be according to the manual. I'm finding that the transport has a really hard time when they are at the right spot. It would seem everything runs smoothly and the ff and rr are more responsive when the left arm is slightly higher than the right whilst in play mode?

I had everything going very nice and responsive, and then the same f5 fuse popped. This time while at the very end of the reel while checking the ff transport functions responsiveness. So maybe the aren't related. But yes, conjecture until we can prove otherwise.

 

[sweetbeats]

I'm not seeing anything discolored or abnormal/heat damaged in the pics of the bias card you posted. They do get quite warm when in record mode. I don't think you have any problem there.

As far as the other issue, maybe you need capture some video so we can see what is happening.

 

[mr.blisset]

okay so i've got the tension arms adjusted to a place that seems alright. The left arm sits slightly higher than the right arm when playing back in the middle of the reel. Given that it seems to respond well going into ff and rw at both ends of the reel I think it's balanced better than ever. I did spend quite a bit of time trying different ways of balancing them and I'm pretty sure I've hit the sweet spot.

However, even in the middle of reel, after a couple mins in PLAY mode I can actually watch the F5 fuse go darker and darker until it glows orange in the middle, it arks and then the fuse pops. It only does this when the tape is moving however.

Given that BIAS pcb looks normal to you, is there anything else I could be looking at? I'm guessing we need to determine which power rail is drawing an abnormal amount of current?

 

[mr.blisset]

okay so I've worked it out. I think maybe it was the heater causing a power spike and blowing the fuses all along. I replaced all the fuses, even the ones that looked fine, and now everything working again. I hope someone in the future will find this thread in google and find it helpful. If a fuse blows, there's a chance another has gone bad also it would seem.