Author Topic: Audio mod fault - very loud!  (Read 1524 times)

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Offline richcheckmate

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Audio mod fault - very loud!
« on: 18:51, 04 January 21 »
Hi all,
    I found a stereo 1m long lead, so I thought I would use one end to plug in to a PC and the other end i snipped off to solder into the 464. I soldered to the points you are supposed to (not  the heads) and all worked great from my PC provided I soldered the left and right together - so the end and the mid section of the plug are linked together and the base ot it is ground.   But when I plugged in my phone or tablet as the audio source neither would output to the 464. I then unsoldered and totally replaced this lead with a 2 wire lead that had a proper mono plug on. when i plugged into my phone it started a high pitch noise and didnt stop! I unsoldered everything to put back to how it should be and the noise is still there.


Next morning the sound had gone and I loaded my harrier attack cassette and all was ok until it finished loading and now the noise is back. what have I done?


I did notice that when harrier attack was loading, it was VERY loud, so much so that I tried to turn it down to silent and you could still hear it.......as if the volume wheel wouldnt turn far enough

It seems that the noise stops when the cassette is loading but when loaded, the noise comes back.  I have noticed that if I leave the 464 for an hour or so, the pitch of this noise gets lower......like it discharging?

What could I have done?


thanks
« Last Edit: 18:57, 04 January 21 by richcheckmate »

Offline Bryce

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Re: Audio mod fault - very loud!
« Reply #1 on: 20:43, 04 January 21 »
It sounds like you've destroyed one of the feedback capacitors. Maybe C316 has shorted, but without having the PCB and a scope it's very difficult to say for sure.

Bryce.

Offline richcheckmate

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Re: Audio mod fault - very loud!
« Reply #2 on: 21:21, 04 January 21 »
Hi,
  thanks for quick reply, not sure how I could have done that then. Anyway, if I buy the whole cassette assemble from ebay, will that fix it.?


thanks

Offline richcheckmate

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Re: Audio mod fault - very loud!
« Reply #3 on: 00:32, 05 January 21 »
Hi, I have just checked and on my board I have linked the two points that are in the attached image.......should these be seperate?


thanks
« Last Edit: 00:35, 05 January 21 by richcheckmate »

Offline tjohnson

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Re: Audio mod fault - very loud!
« Reply #4 on: 10:20, 05 January 21 »
It looks like they are part of the same trace, do you have any solder flux wick or a solder sucker you can use to remove the solder to check?

Offline richcheckmate

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Re: Audio mod fault - very loud!
« Reply #5 on: 10:43, 05 January 21 »
Hi,
    I dont, not yet, but I ill buy some if I need to.   But if they are part of the same track, then it doesnt need to be seperate .....or am I missing something here?


thanks

Offline Bryce

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Re: Audio mod fault - very loud!
« Reply #6 on: 11:14, 05 January 21 »
It's hard to tell from the picture, but it looks like that solder bridge would short the red and black wire, which would definitely be wrong.

Bryce.

Offline richcheckmate

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Re: Audio mod fault - very loud!
« Reply #7 on: 11:34, 05 January 21 »
Hi,
     I just found this and it looks to me that I havent done anything wrong as the track is indeed connected to the 2 point (I have highlighed it).    Bryce, do you mean the black and red that go to the red LED.....they are not shorted, will put another pic on for you


thanks

Offline Bryce

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Re: Audio mod fault - very loud!
« Reply #8 on: 11:51, 05 January 21 »
Ok, the red line you drew was hiding the break in the trace. Why did you remove the bridge that connected those two holes though?

Bryce.

Offline richcheckmate

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Re: Audio mod fault - very loud!
« Reply #9 on: 12:03, 05 January 21 »
Hi,
   I was wondering that when I saw the bridge on the diagram.....the 2 holes are there but no bridge. I havent removed anything.  shal I put a bridge in? 


thanks
« Last Edit: 12:12, 05 January 21 by richcheckmate »

Offline Bryce

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Re: Audio mod fault - very loud!
« Reply #10 on: 12:23, 05 January 21 »
It looks like it was never there. You'd need to compare it with a working cassette PCB.

Bryce.

Offline Chinnery

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Re: Audio mod fault - very loud!
« Reply #11 on: 14:37, 05 January 21 »
I've just checked the tape deck I have here and there is no bridge on this one either, nor is there any continuity between the two points.
(Ignore the yellow wire, that's another project...)

Offline richcheckmate

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Re: Audio mod fault - very loud!
« Reply #12 on: 15:06, 05 January 21 »
Hi,
   thats great then....nothing missing on mine, tanks for checking. I dont suppose you could check on yours to see if there is continuity between the two points I have highlighted in red?  Just to to make sure ?


many thanks

Offline Bryce

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Re: Audio mod fault - very loud!
« Reply #13 on: 15:29, 05 January 21 »
Do you have any test equipment to measure the outputs and DC bias of the op-amps?

Bryce.

Offline richcheckmate

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Re: Audio mod fault - very loud!
« Reply #14 on: 15:45, 05 January 21 »
Hi,
   I have only a multi-meter I am afraid.


thanks

Offline Chinnery

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Re: Audio mod fault - very loud!
« Reply #15 on: 16:08, 05 January 21 »
Hi,
   thats great then....nothing missing on mine, tanks for checking. I dont suppose you could check on yours to see if there is continuity between the two points I have highlighted in red?  Just to to make sure ?


many thanks
The two points you mentioned earlier do have continuity, so I don't think you've accidentally bridged something there.

Offline richcheckmate

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Re: Audio mod fault - very loud!
« Reply #16 on: 16:21, 05 January 21 »
Hi,
     thats great, at least I know the fault doesnt lie there then, thanks for checking for me.......no idea why this is happening


Rich

Offline richcheckmate

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Re: Audio mod fault - very loud!
« Reply #17 on: 10:37, 06 January 21 »
Hi all,
    am i buggered then here......can I buy a working tapedeck from ebay .....will that fix it?


thanks

Offline richcheckmate

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Re: Audio mod fault - very loud!
« Reply #18 on: 19:03, 09 January 21 »
HI all
         I have swapped the tape deck over with another one, and my 464 is running perfect, so the fault is only on my original tape deck.  Pity I cant keep this tape deck in it......but that would mean buggering up this 464.     


Also the sound is still loud and constant...but at a lower pitch now, is this a doomed tape deck?


thanks

Offline Bryce

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Re: Audio mod fault - very loud!
« Reply #19 on: 19:28, 09 January 21 »
No, it's probably just a failed/shorted op-amp. Send it over to me if you like and I'll sort it out for you.

Bryce.

Offline richcheckmate

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Re: Audio mod fault - very loud!
« Reply #20 on: 11:28, 13 January 21 »
HI,
  This bonkers but, I resoldered the joints around the op amp, and also the the wires that go to the main board. Put back together and it worked perfectly. Loaded harrier attack on both sides! Tested sound from "DEL" key.     All fixed!    I left it alone for an hour or so and fired it up with another game and I started getting read error "a". So I went back to the harrier attack that loaded earlier and that too started getting read errors. After a few mins of trying to load the other side, nothing was loading. Now, no sound is coming from the tape drive at all. "Del" sound still works,


I ordered the chip "Bryce" recommended and am waiting for delivery of it.......but this all worked for while, anyone one know whats going on?


thanks