Help repairing Fisher 1265x

[Koala]

U303 there's a dead short between pin 5 and 6


Can't see on the schematics. Am I missing something ?


Dam they are suppose to be connected.

All transistors and diodes look okay. I will keep looking

[Koala]

Pin 13 of U401 I get 411Hz and 7 Vpp almost square wave. So guess the audio oscillator is functioning okay. Although I never get a proper been in any mode

[Koala]

Pin 9 of U401 look badly wrong. It's got supply volts on it ???

[Koala]

Feel like an idiot.

Testing the ribbon cable to the front panel everything was measuring wrong.

I had put the cable on 180 degrees out. I don't remember the twist in the cable at all. It was a few weeks before my parts arrived.

Lucky to get away with it. It is working as it was.

[Koala]

Setting

There is still annoying problem that has always been there

Disc on full. Swing large iron close to the coil it discs out correctly but as you move it away it starts to give a faint signal.

[Nandor]

It looks like Dave Johnson is not online, have you contacted him?

[Koala]

Still not working at its full potential

Static mode isn't. Target signals fades after about 2 seconds POT R305 does nothing. +8 and GND are correct. Depth is very poor.

Switching from disc 1 to disc 2. Cause something like a battery beep which fades after about 2 seconds and then starts working normally. Depth is very good 15" on a pre decimal penny

.

[Koala]

Some progress.

Changed C303.

Measures spot on with a component tester. But changed it any way.

Static mode is now static for the first time since I got the machine. Depth in static mode had increased and I can now get a threshold tone.

[Koala]

Weather was bad for ages here in the UK but now its picked up i have put about 40 hours on this machine since it was repaired

Everything is great. Depth and discrimination.

However it has failed twice.

First time was part of the original problem. Continuous beep in disc 1 but okay in disc 2 this lasted for about 5 minutes. I was over a target when it failed. Even though it was beeping if would go louder when sweeping over the target. It would appear to be working in static mode as when sweeping slowly the tone rises for longer than expected


The second time it failed it was towards the end of 8 hours detecting. For about 15 minutes the tone sounded terrible crackly static type beep. Which cleared up and worked correct again.


This is the schematics that match my machine.

[Koala]

Should be able to work this out without randomly changing capacitors.

I guess the extra load of R331 is why disc 2 continues to work while disc 1 fails.



U303 and switch have been changed.

Thanks in advance

[Koala]

still not sorted this out

did another 8 hours with the detector

first 5 hours or so and it was working fine

then started to sound strange. longer broken tones.

last couple of hours was unusable.

might be a hint here in the setup

Set Static Threshold fully anticlockwise.
Set Disc Bias fully anticlockwise.
No audio should be heard at this point.

mine makes a beep unless I turn either the static or disc away from there end points

and maybe another hint the disk 2 has always been more reliable than disk 1

[waltr]

Battery Voltage dropping TOO LOW???

[Koala]

Battery Voltage dropping TOO LOW???

Mmmmm I will check.

I do press the battery check from time to time and that's still loud even after its failing.

Just tested volts and they are 10.77 but that's after a bit of bounce back. left the speaker buzzing a way on the battery check for a bit and now its on 10.74

I will leave it on for a bit and check the power rails.

[waltr]

What type and number of cells in the battery?

10.77V/8 = 1.34V a bit low for alkaline

10.77/10 = 1.07 too low for NiCad or NiMH.

10.77/3 = 3.59 way too low for LiPo or LiIon

[Koala]

What type and number of cells in the battery?

10.77V/8 = 1.34V a bit low for alkaline

10.77/10 = 1.07 too low for NiCad or NiMH.

10.77/3 = 3.59 way too low for LiPo or LiIon

Yep been in awhile. However is still pumping out a heathy 8 volts on the power rail.