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Old 16th Feb 2017, 9:12 am   #61
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Default Re: Defiant MP4 with AT6 Turntable refurbish

Graham.

The coupling capacitor C3 will be connected between pins 1 and 9 of the UCL83.
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Old 16th Feb 2017, 9:22 am   #62
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Default Re: Defiant MP4 with AT6 Turntable refurbish

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Originally Posted by Edward Huggins View Post
This is such a basic circuit that I'm sorry to see the OP struggling with it.
Edward.

I think that comment is unfair. Not all record player faults can be fixed by changing the cartridge. The reason the OP "struggled", as did I, is that the circuit diagram he downloaded wasn't correct for his particular model of player. Furthermore the differences were in the power supply area, which as it turned out was the very area where the fault was.

I had to reverse engineer the circuit by looking at pictures of the transformer and asking questions about where various wires went to. The presence of the lamp, whatever its function may be, was unknown to me and is a vital part of the HT supply circuit.

The OP has demonstrated that he can follow advice, identify valve pins and take readings of voltages and resistances. I have no doubt that if the player fails again he will know exactly where to start looking for the fault.
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Old 16th Feb 2017, 10:08 am   #63
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Default Re: Defiant MP4 with AT6 Turntable refurbish

Regarding the "Indicator Lamp".

This will have to carry the full HT current, which for a UCL83 is about 35mA. If the lamp is to light fully it will need to be 6V 0.2W or 12V 0.4W, assuming these or something similar are available. Using a higher voltage lamp would result in an unacceptable drop in HT voltage.
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Old 16th Feb 2017, 10:46 am   #64
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Default Re: Defiant MP4 with AT6 Turntable refurbish

Graham

I do sincerely apologies if I have caused you any 'friction' with other users, this was never my intention.

My previous career was not in electronics and I haven't dabbled for many years with valve equipment. I have however enjoyed our discussions and am feeling more comfortable with the device for which I do thank you for your time and patience.

A new 25uf polarised capacitor (care of RS) turned up this morning and I am looking forward to at last getting my soldering out !!!

I now need to get hold of a replacement lamp and without a correct circuit diagram will start with a 6v 0.2w do you concur? I will also remove c3 and post the resultant voltage.

Kind regards
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Old 16th Feb 2017, 10:51 am   #65
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Default Re: Defiant MP4 with AT6 Turntable refurbish

Noting the comments in Post#62, I'm really sorry if I appeared to be patronising.
Many of us had identified a power power supply issue early on and the OP has needed to really persevere with this, for which all credit is due. Also I must have missed the fact that he did not have the correct circuit diagram. Mia Culpa!
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Old 16th Feb 2017, 11:45 am   #66
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Default Re: Defiant MP4 with AT6 Turntable refurbish

Graham.

I must admit that I can't explain why the lamp lit before, does not light now and yet the player is working. It's possible the lamp is short-circuit, but this would be an unusual failure mode.

You could measure the AC voltage across the lamp by connecting your meter to tags 3 and 6 of the mains transformer, these being wired to the lamp. Also a resistance reading of the lamp's filament (out of circuit) might enable its spec to be determined. You could also check whether it can be lit using 1.5V batteries, progressively connecting them in series.

When you've replaced the 25uF cap, check the resistance of R4 (390R) which is wired in parallel with it. The reading will start low because your meter will be charging the capacitor, but should settle after a few seconds.

When you've applied power check the voltage across R4. Divide this by 390 to give the combined anode and screen currents of the pentode section of the UCL83.
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Old 16th Feb 2017, 11:57 am   #67
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Default Re: Defiant MP4 with AT6 Turntable refurbish

A thought crossed my mind about the transformer in the photo. It looks to be pitch coated which suggests it's possibly of Philips origin. I wonder if it's been used as a replacement at some time and is not original.
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Old 16th Feb 2017, 12:21 pm   #68
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Default Re: Defiant MP4 with AT6 Turntable refurbish

In my experience all the mains trannys of these Defiant (Plessey) made amplifiers of this period used this rather good quality component as original equipment.
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Old 16th Feb 2017, 12:27 pm   #69
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Default Re: Defiant MP4 with AT6 Turntable refurbish

The lamp is wired across tag3 and tag6 and with lamp 'in circuit' I get 4.6vac and with the lamp 'out of holder' I get 7.18vac across the tags. I am assuming that's probably ok?

When I test for resistance across the bulb 'out of bulb holder' I get zero ohms but when I test it with the meters audible beeper on I get beeps. I have been unable to get it to light with batteries - which all sounds a bit contrary to me?

I have fitted the new capacitor and tested the player - all still good (accept the sound is a bit muffled as it always has been) but plenty of volume and no hum.

I am unable to locate any 'parallel' wired resistor?

A thought did occur to me - could it be that somebody else has retro fitted the mains isolating transformer and adjusted the circuit along the way? it doesn't look particularly retro fitted in side though as all the soldered joints seem original?

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Old 16th Feb 2017, 12:30 pm   #70
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Default Re: Defiant MP4 with AT6 Turntable refurbish

Hi vidjoman

Thanks for your response, its beginning to feel that way I must admit we cant seem to find any circuit diagrams that match?
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Old 16th Feb 2017, 12:37 pm   #71
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Default Re: Defiant MP4 with AT6 Turntable refurbish

Graham

Just to add something else - its been on now for 15mins and the transformer is now hot to the point that I scalded the tip of my finger on the body of the windings - everything still working fine though. (I have now turned it off).

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Old 16th Feb 2017, 12:53 pm   #72
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Default Re: Defiant MP4 with AT6 Turntable refurbish

Quote:
Originally Posted by ggg1234 View Post
The lamp is wired across tag3 and tag6 and with lamp 'in circuit' I get 4.6vac and with the lamp 'out of holder' I get 7.18vac across the tags. I am assuming that's probably ok?

When I test for resistance across the bulb 'out of bulb holder' I get zero ohms but when I test it with the meters audible beeper on I get beeps. I have been unable to get it to light with batteries - which all sounds a bit contrary to me?
Once again I'm at a loss to explain this. If the lamp has zero resistance and won't light from batteries, it has probably failed short-circuit, which as I've said would be a most unusual failure mode. Can you actually see the intact filament within the lamp?

If the lamp has zero resistance there won't be a voltage across it. It's possible that 4.6 VAC is being dropped in the yellow wires, but this would require a very high current.

As I say I'm at a loss here. Perhaps Edward can help?

Quote:
Originally Posted by ggg1234 View Post
I am unable to locate any 'parallel' wired resistor?

Graham
I had assumed, perhaps incorrectly, that the 25uF capacitor was the cathode bypass capacitor for the pentode section of the UCL83. That being the case there would certainly be a cathode resistor in parallel with it.

I think you're going to have to post some clear pictures of the underside of the chassis so that we can reverse engineer the circuit and produce a correct circuit diagram.
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Old 16th Feb 2017, 1:19 pm   #73
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Default Re: Defiant MP4 with AT6 Turntable refurbish

Assumed transformer wiring. Constructive criticism welcomed.
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Old 16th Feb 2017, 2:42 pm   #74
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Default Re: Defiant MP4 with AT6 Turntable refurbish

I notice you said earlier it had a "muffled" sound which is unusual, it should sound quite bright needing the tone control to "tame" it. I'm not sure how the tone control is wired on this but the tone control capacitor may have increased in value. If it is wired across the OPTX primary, this might be having an effect on the HT draw?
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Old 16th Feb 2017, 4:01 pm   #75
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Default Re: Defiant MP4 with AT6 Turntable refurbish

Hi Graham

Pic 1. Is of the lamp as close as I can.
Under a jewellers loop it looks attached at both ends to me. My new DMM meter gives it the same reading (00.0 ohms) as touching the probes together. This would mean continuity - yes? but with a PP9 9v battery it wont light.

Pic 2. Whilst under the jewellers loop I noticed some faint writing which looks like 12v?

Pic of base of circuit board to follow. . . .

Graham
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Old 16th Feb 2017, 4:50 pm   #76
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Default Re: Defiant MP4 with AT6 Turntable refurbish

Hi Graham

Here are some circuit board pics. please let me know if you need angles / different views.
Kind regards
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Old 16th Feb 2017, 5:07 pm   #77
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Default Re: Defiant MP4 with AT6 Turntable refurbish

Graham.

Not enough detail I'm afraid. Can you take close up pictures showing the components on each valve holder and the smoothing caps please. Use your camera's "macro" setting, often denoted by a flower symbol if it has one.
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Old 16th Feb 2017, 5:12 pm   #78
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Default Re: Defiant MP4 with AT6 Turntable refurbish

Quote:
Originally Posted by Edward Huggins View Post
I notice you said earlier it had a "muffled" sound which is unusual, it should sound quite bright needing the tone control to "tame" it. I'm not sure how the tone control is wired on this but the tone control capacitor may have increased in value. If it is wired across the OPTX primary, this might be having an effect on the HT draw?
The tone control cap in this set is that nasty looking 0.02uF Hunts. It's wired from the anode of the pentode, through the tone control and then to chassis.
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Old 16th Feb 2017, 5:21 pm   #79
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Default Re: Defiant MP4 with AT6 Turntable refurbish

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Originally Posted by ggg1234 View Post
I am unable to locate any 'parallel' wired resistor?

Graham
I think you'll find the parallel capacitor is wired to pin 7 of the UCL83 as is the 25uF electrolytic. The resistor passes at right angles under the brown 0.02uF Hunts capacitor and presumably the other end goes to chassis?
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Old 16th Feb 2017, 5:53 pm   #80
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Default Re: Defiant MP4 with AT6 Turntable refurbish

Hi Graham

Apologies I only have my phone camera here but I attach about the best quality it can do.

I think also it might be better in daylight tomorrow as I am getting black shadows under these lights. What do you think of the detail of the attached do we need better?

Regards
Graham
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