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Repurposing vintage hifi cases

folzag

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#1
Greetings folks,

I bought a Pioneer CT-F700 on eBay from a local seller. It is not completely working, so only cost me $20. But hey... 3 VU meters!!

As a first iteration, I'm thinking it would be pretty cool to house a Khadas DAC & JDS Atom. A future improvement would be to add a Hypex amp -- it's huge inside there.

I can tell someone has been in there before trying to fix it, but they appear to have been a hack:
* stripped one of the screws holding the faceplate
* re-attached faceplate off-center
* output adjustment pot is slightly loose
* right VU is slightly loose

There are a couple things I want to determine before making a decision on how to proceed.

1. Adjusting the input pot will sometimes pop and crackle and peg the VU meters. Internal oxidation? Is there a typical way for dealing with that?

2. The outer knob on the input/output pots comes off, but the inner knob does not. Also, instead of the inner and outer being separately adjustable for L & R channels, they are fixed together somehow. Has anyone seen something like this? Seems like whomever hacked on it previously did something here for some reason. I haven't tried prying on the inner knob yet as I don't want to break anything. It is weird and the two things together have me wondering if there's something going on. You don't suppose someone glued it up do you?

3. The left channel output VU works fine, but right channel VU never moves. The right channel is passing sound properly to the headphone, so need to track down where the failure is. (That the right VU happens to be the loose one makes me suspicious someone tried working on it already.)

Any advice, including web sites for this kind of thing, graciously appreciated. Thank you.
 
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Doodski

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#2
1) Get some control cleaner lubricant and spray it inside the pot.(don't use NuTrol, it dries up after a year or two and makes the pot stiff)
2)Somebody might have glued it or used some paper to make it fit tight. Are you sure there is no set-screw?
3)The inoperative VU meter might have a capacitor in the signal path or some other cause for cutting off the signal. Do you have a oscilloscope?
 

folzag

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#3
1) Thx. Preferred brand or URL?
2) Not that I saw, but that was partly my concern... given the inner & outer aren't moving independently is there some sort of hidden set screw all the old-hands know about, but I missed. If that's "not a thing," I will try (gently) prying next, but wanted to check the wisdom of the internet first.
3) I do have a scope, which is nice. :)
 

Doodski

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#4
1)Just a good control cleaner that your local electronics supply offers.
2)Be very careful ;)
3)Using the oscilloscope probe about the connectors and capacitors on the VU meter PCB region to see if you can find a signal. Best is if you have a sine wave but a musical signal will work. In the past I have found old little electrolytic capacitors in the VU circuitry that have shorted and caused the VU meter signal to be shorted. That's a good start. If you can't find a signal then go back in the main input circuitry till you do find it and then start dividing and conquering. meaning you'll need to unsolder along the signal path to find where it goes dead and then continue doing that till you find the cause.
 

Doodski

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#6
Oh there's one at your link.. I'm just waking up here from a late night of furnace belt being broken in the night.
 

Doodski

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#7
VU meters signal comes from the REC/PLAY switch. Before getting all fancy and stuff that should be cleaned and lub'd. Clean and lub all controls and then we'll see how things go. There's a good chance the REC/PLAY switch is the cause of the VU meter showing no signal.
 

folzag

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#8
Yeah, manual said they just slide off. Krazy glue occurred to me as I was typing this up and making the list of hacks. o_O

Yes, I got the REC/PLAY part figured out. The left VU meter worked fine, which makes me think it's something in the signal path to the right one... though I suppose if it has 1 switch per channel, maybe one switch is good and one is bad. Though, again, left ch. on the headphone is fine. It's just the VU meter.
 

folzag

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#12
Don't know yet. But, yeah, I need to answer that question first. I reckon start there and work backwards... or forwards if it is getting a signal, but is dead. I'm thinking if the VU itself is dead it's a replace-only item?
 

Doodski

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Don't know yet. But, yeah, I need to answer that question first. I reckon start there and work backwards... or forwards if it is getting a signal, but is dead. I'm thinking if the VU itself is dead it's a replace-only item?
Yes, usually a replace only item. But some might venture forth, disassemble it and poke about inside looking for a fault. You have nothing to lose if it is the VU meter by checking it for something wrong internally.
 

folzag

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#14
Check for signal at VR304.
OK, good news: no glue, just took some extra carefulling to get knobs off.
As for VU meter... good signal on wire-wrapped pins 17 & 18 & 19 -- headph L / R & VU L, no signal on pin 20 -- VU R

Unwrapped wire on pin 20.
No signal on it w/o the meter connected. Strange, does it need a load?
Holding the wire to pin 19, as soon as the wire touches the left VU drops to 0. Can't drive two loads?

I guess I'll unwrap pin 19 and swap them. I don't have the tool to re-wrap them though.
 
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Doodski

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#15
Let's see what happens after you swap the pins 19 & 20 going to the rec level meters. You can re-wrap them manually and then solder them if you like.
 

folzag

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#16
Let's see what happens after you swap the pins 19 & 20 going to the rec level meters. You can re-wrap them manually and then solder them if you like.
Looks like it's the VU meter. :( Left VU works fine on either pin. Right VU does nothing on either pin.
 

folzag

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#20
I reckon nothing left to loose. Sounds like the coil has shorted, maybe from the scratchy input pot on the part of a former user.
 
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