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HMV 2638- Another 960

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Focus Diode
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Just got back from a very enjoyable journey down to Steve's with David B. I'm sure they'll fill you in with the highlights of the visit.

I returned with a HMV 2638. Although more complete than the 2633 it's been stored in damp conditions with much internal rusting. Like Jon's Ferguson it's the later version with the dropper resistor and card back cover. Unlike Jon's there's a cover for the line output stage.

However tempting it may be to keep this one for spares for the earlier version with its 3 minute warm up time this has to be resisted. The 2638 has every right to live again.

I'll be starting work on it soon.

Thank goodness it doesn't have a silver CRT surround!

Brian

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Topic starter Posted : 04/11/2018 1:19 am
Focus Diode
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Been able to dismantle the set for further investigation. I see it uses the same unprotected type of CRT as in the earlier set but sensibly it's properly guarded rather than the crude implosion sheet on the 2633 version.

Cutting the mains filter capacitor which is buried under the on-off switch and some cold checks suggested the set was ready for waking up, courtesy of a lamp limiter.

A faint glow could be seen in the EF80, but no other activity. Try again and the PL500 gave a very pretty display!

Fit replacements and try again. No further arcing 

Time to apply full mains.

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Topic starter Posted : 04/11/2018 6:15 pm
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Focus Diode
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And we have first light.

I'd forgotten how intense the 405-line is with the original Lopt.

As can be seen much work is going to be needed!

Brian

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Topic starter Posted : 04/11/2018 6:22 pm
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Nuvistor
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Was the Mazda Goldstar crt Mazda’s factory rebuild?

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Posted : 04/11/2018 6:41 pm
PYE625
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The attractive blue glow inside the PL500 reminds me of a mercury arc rectifier. 

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Posted : 04/11/2018 7:43 pm
Focus Diode
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I think it's the original Frank. The Mazda CME bit is unreadable due to the mounting damaging the label. I think following the problems with the earlier version they adapted the later 16" sets to be properly fitted with a Feinbridge guard wrapped around the faceplate as in 19" and 23" models.

The good news is, it looks to be in excellent condition.

While making quick checks a new PCL805 failed to make any difference to the rolling frame and lack of height, nor did bridging the PCL85 cathode bypass capacitor. The valve found in the set is a '60s Mullard PCL85, the only non original valve I've encountered upto now.

The PCL86 gave up the ghost, no sound with an overheating cathode bypass capacitor. Replacement cured the problem.

Unlike the 2633 there's very little, if any previous service work undertaken with the set, apart from the old style Mullard PCL85. The PL500 certainly looked to be the original one. Rather a shame it turned out to be faulty but pleased I captured it on camera before it had to be disposed of.

 

Cheers

Brian

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Topic starter Posted : 04/11/2018 8:43 pm
PYE625
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Sometimes, a gassy valve may clean up due to the getter action becoming more active as it is warmed in use. This however, is not always the case of course. But I had a new PCL85 that showed quite a healthy blue glow, coupled with a poor output, that cleared after a few minutes of use. That same valve is fine now and fitted in my Decca DR303.

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Posted : 04/11/2018 10:12 pm
Focus Diode
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I've seen that myself Andrew. The French Mazda PL504 fitted in the 2633 gave a lovely shade blue within the usual colour when first fitted.

The valve in the 2638 was arcing badly, giving a blue firework display inside the glass. This was before full mains was applied! I wasn't prepared to test it on full mains with these symptoms without fitting different valves first.

So, what do we have so far? Rapidly rolling frame, cramping, lack of width and hum on sound. Plenty to be getting on with. I'll do the frame and sound stages first.

Cheers

Brian

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Topic starter Posted : 05/11/2018 9:58 am
Focus Diode
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Interesting. The cabinet colours between the 2633 and 2638 are indeed are nearly negative images of each other.

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Topic starter Posted : 05/11/2018 2:04 pm
Focus Diode
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Not much progress tonight apart from sorting out the frame unlock courtesy of R98 (390K). The appalling non-linearity persists. They are of course many more components in need of replacement.

The cause of the distraction was a new fault. Fuse blowing at switch on. I checked and re-checked the work I'd done in case I introduced a major short. 

Eventually found a chassis connection lead shorting to one of the leads of the HT rectifier.

Annoying when this kind of thing happens as you spend the limited time looking for the cause that could've been spent on the frame panel.

Happens to us all at sometime!

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Topic starter Posted : 05/11/2018 6:59 pm
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Focus Diode
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The photos show up two faults. It initially comes on stable, allowing for the cramping then soon becomes this twisted mess.

I've had the latter before due to C43 (0.1uf), the sync separator grid coupling capacitor.

The whole lot of these types on the main board will have to be replaced of course.

There's hope the '60s Mullard PCL85 will be ok.

Photos are reversed IE the wobbly mess appears after a few minutes.

Brian.

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Topic starter Posted : 06/11/2018 11:38 am
malcscott
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Plenty of NOS PCL805 here. PM me if you need any, Malc.

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Posted : 06/11/2018 12:13 pm
Focus Diode
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Very kind of you Malc, many thanks. Think I have a few spares on me but I'll check.

The symptoms were identical when a new PCL805 was tried. I'm confident the set will be displaying fully scanned images shortly. C43 will also have to be changed of course to achieve a stable locked image.

I'll get back to it on Monday when I'm next off.

Cheers

Brian

 

 

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Topic starter Posted : 08/11/2018 11:09 pm
Focus Diode
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Big improvement on replacing all the components on the top of the frame chassis. The frame output transformer had to be removed to gain access to some components.

Without any 0.033uf capacitors, I tried 0.047uf in the C90 position.

Replacing C43 should solve the wobbly image which I'm about to do now.

Brian

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Topic starter Posted : 12/11/2018 2:07 pm
Focus Diode
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Lovely!

Still plenty to do of course. The frame is liable to drift, might be the valve after all!

Brian

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Topic starter Posted : 12/11/2018 2:46 pm
Focus Diode
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It was the PCL85 so the tried and tested HRS PCL805 has now found a permanent home at last. I was beginning to feel sorry for it!

Ignoring the lack of width I was able to achieve improved frame linearity. I'll leave the line output stage well alone until my order for 1KV rated capacitors etc. arrive.

The audio output stage is in a sorry mess. Low audio with loud hum. Best I tackle that next seeing I've already had to replace the PCL86, not wishing to damage the replacement one.

I'm certainly enjoying working on this set more than the 3645 1400 model. Goodness knows why as accessibility is horrible in comparison!

Cheers,

Brian

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Topic starter Posted : 12/11/2018 3:08 pm
Focus Diode
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Replacing components in the sound output stage gave no significant improvement. I then discovered the volume control itself has ceased solid. No amount of lubrication will free it, so will have to be replaced.

Gives an idea of the past storage conditions. The other controls are fine however.

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Topic starter Posted : 12/11/2018 6:38 pm
Focus Diode
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The two sets side by side.

The 2633 looks thinner due to the camera angle.

Will get back to the 2638 next week with a test on 625-lines. A good clean up will be done too.

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Topic starter Posted : 26/11/2018 9:03 pm
Focus Diode
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A run on 625-lines UHF revealed all to be well as far as the system switching and UHF tuner is concerned. Unable to set the contrast at this stage as the retainer prevents a control knob to be fitted which will be attended to in due course.

The 625 scan correction capacitor will also be changed.

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Topic starter Posted : 04/12/2018 5:08 pm
MurphyV310
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Brilliant results.

A couple of questions...... What colour is the LOPTY in the 960 and is it a single diode or multiplier?

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Posted : 04/12/2018 8:28 pm
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