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-   -   Beovision 7102 CRT TV,schematic/advice please (https://www.vintage-radio.net/forum/showthread.php?t=126284)

zens.tv 10th May 2016 10:44 am

Beovision 7102 CRT TV,schematic/advice please
 
TYPE 7423

hi all,

this set not powering,some EHT produced,then shuts down

H.T of 165 volts,measured across C7

anyone recall what this model suffers with ?

my knowledge on CRT sets is very hazy,at best

zens.tv 10th May 2016 11:43 am

Re: Beovision 7102 CRT TV,schematic/advice please
 
1 Attachment(s)
discovered D15 ( BY584 ) to be O/C

found BY203,equivalent @ RS components

Nickthedentist 10th May 2016 7:34 pm

Re: Beovision 7102 CRT TV,schematic/advice please
 
A lot of arcing going on around one leg of C47 too? Or is that the pic?

zens.tv 11th May 2016 9:34 am

Re: Beovision 7102 CRT TV,schematic/advice please
 
hi Nick,yes

a previous repair me thinks,as cap had been replaced,but it's in line with D15,which i suspect had been weakened & now decided to fail

zens.tv 17th May 2016 1:50 pm

Re: Beovision 7102 CRT TV,schematic/advice please
 
red herring i'm afraid

diode is ok.only realized after replacement arrived.doesn't measure on meters diode setting,due to the fact it has a high forward resistance

steve1010uk 17th May 2016 2:08 pm

Re: Beovision 7102 CRT TV,schematic/advice please
 
Not sure if it's connected to your fault or not but i seem to remember those brown electrolytics had a nasty habit of going short circuit.

Steve

zens.tv 17th May 2016 3:44 pm

Re: Beovision 7102 CRT TV,schematic/advice please
 
hi Steve,

checking through the PSU and line output circuitry at the moment,but nothing yet

starting to suspect LOPTX

zens.tv 18th May 2016 9:30 am

Re: Beovision 7102 CRT TV,schematic/advice please
 
at the workshop till 9pm last night.

tested all components on line,power supply,east west & tube base modules

all checked out ok

suspect LOPTX

its a PHILIPS AT2076/70A

HR equivalent = HR6070

Welsh Anorak 18th May 2016 11:55 am

Re: Beovision 7102 CRT TV,schematic/advice please
 
Hi
That's similar to (but not the same as) a G11 LOPT, isn't it? Try running it with the EHT lead removed from the transformer - be careful as the 'pip' on the end of the lead can come off. These LOPTs are pretty reliable but the EHT lead isn't.
Glyn

zens.tv 18th May 2016 2:51 pm

Re: Beovision 7102 CRT TV,schematic/advice please
 
thanks Glyn,will do

have been informed transformer very similar to a TX10

Marconi_MPT4 18th May 2016 10:56 pm

Re: Beovision 7102 CRT TV,schematic/advice please
 
Quote:

Originally Posted by zens.tv (Post 846575)
TYPE 7423
anyone recall what this model suffers with ?

Hi,
Many, many dry joints on the power (6), control (46) and mother (60) boards.

5D15 and 5C47 on the line and field deflection unit, supplies CRT A1 circuitry with 750V from line flyback. Occasionally 5T11 can fail, but design was improved on later production PCB. 5TR3 (BU208) metal case corrodes which then punctures insulating mica washer causing flash over. More often faults are the result of liquid contamination due to spillage from over zealous watering of a potted plant. Also occasionally from a leaky cat.

When shut down occurs, does the power control circuit try to cycle about six times before locking out? You should hear the power transformer tick on each try. There are over/under voltage and over current safety trips on this set. For instance, Pin 6 of 46IC1 deals with over current protection and has to go above 0.7V to invoke trip.

Quote:

Originally Posted by zens.tv (Post 846575)
H.T of 165 volts, measured across C7

Is that capacitor 6C7? If so should have 295V across it measured directly on both tags.

Check carefully when using an apparently similar transformer as a substitute as sometimes the B&O pin out can vary.

Cheers
Rich

G8KBG Tony 18th May 2016 11:40 pm

Re: Beovision 7102 CRT TV,schematic/advice please
 
If the LOPT is faulty, Donberg still sell the HR6070.

Tony

zens.tv 19th May 2016 9:20 am

Re: Beovision 7102 CRT TV,schematic/advice please
 
thanks for the info Rich,will carry out some further tests

cheers Tony,yes spotted it.have ordered from them on a few occasions and very happy with the service

flyingtech55 23rd May 2016 7:10 am

Re: Beovision 7102 CRT TV,schematic/advice please
 
Just a quick comment....

I don't want to be pedantic but the thing on the power supply PCB, although it looks like one, is not the LOPTx. It's the EHT generator. It also produces a number of other supplies including that for the sound output stage. The LOPTx is actually on the small PCB on the bottom of the cabinet under the CRT. As I say, I'm not being pedantic, it just used to cause a lot of confusion back in the day.

You mention that you have only 165V across 6C7. If that is the main smoothing block after the bridge rectifier comprising 6D1, 6D2, 6D3 and 6D4 then that is your fault. There must about be a solid 300V (or there about) across that capacitor. Do not bother doing anything else until you have 300V across that capacitor. It has probably gone O/C or the bridge rectifier is half waving. It wasn't common back in the day but age will take its toll. The set will not run with only 165V on the main HT rail. Get the fundamentals right before you start randomly changing parts. You must have the full 300V main HT rail up or you are just wasting your time.

After that, for tripping, the three most important things to check are dry joints, dry joints and finally, dry joints. These were particularly common on the little edge connectors that the larger boards plug into. If not these, then unplug the EHT cable. These are a common cause of the symptom you describe. The set starts up the then almost immediately shuts down. ISTR that the set shuts down and doesn't 'pump'. When you switch the set off and then back on, the behaviour is repeated. As Glyn says be careful not to pull the 'pip' off the end of the EHT cable. The EHT transformer is very reliable and the only ones I renewed were because of physical damage due to dry joints arcing (did I mention dry joints) or because the 'pip' had fallen down inside the stub and was causing 'brushing'. I never had one break down as such. However, these sets are getting on a bit now so I suppose these things can begin to fail.

HTH

TimR

zens.tv 4th Jun 2016 2:27 pm

Re: Beovision 7102 CRT TV,schematic/advice please
 
1 Attachment(s)
thanks for all the advice guys

good and bad news on this one

another check with fresh eyes

made an error before. C7,did in fact have 330V across it,which is correct

fault was actually due to a dry joint,on link FE4

not sure how i missed it,as i had previously reflowed most of the power supply/line output module

anyway,power was then restored,and set ran ok,for about half an hour,then scan coils began to cook,literally.i could see some smoke.

think i'm going to call it a day on this one

MALC SCOTT 4th Jun 2016 4:36 pm

Re: Beovision 7102 CRT TV,schematic/advice please
 
It could be just the plug/socket on the coils dry jointed.

Clydeuk 5th Jun 2016 1:25 pm

Re: Beovision 7102 CRT TV,schematic/advice please
 
I don't know this set at all or what CRT it uses, but back in the 90's I was regularly seeing sets (mainly smaller screen types) with scan coil failure due to arcing, caused by corrosion where the rubber wedges go. It seems that after a while the wedges start to deteriorate and in doing so release some chemical that then dissolves the coating on the copper, resulting in arcing and eventual shorted windings. The usual failure mode was that the set would come in the the Horizontal output transistor short-circuit. Relplacement would result in arcing and a repeat problem.

I'm not saying this is your problem, but other than this problem I found scan coil failure to be rare. If yours is wedged on it might be worth removing the wedges to see if there is any evidence of decomposition.

Clydeuk 5th Jun 2016 1:36 pm

Re: Beovision 7102 CRT TV,schematic/advice please
 
Just done a google image search, found a Beovision 7100, not sure if that's the same set? Anyway I remember these and as I remember it they use the 30AX Mullard CRT, so the wedge comment above doesn't apply.

Now I never experienced scan coil failure on these CRT's, but I suppose there's always a chance, it's probably 20 years since I last worked on a set using this CRT.

However, if the scan coils have failed you should have little trouble finding replacements. I'm sure the coils were the same on every 30AX I encountered. This particular CRT was fitted to a huge range of models from many manufacturers. You'll find this CRT in most Ferguson TX10/TX100 22 and 26 inch models, Philips used it in their K30 and K40 models, Sanyo and Amstrad also used it in 2 very unreliable models (which were always a great source of a good tube)

Maarten 5th Jun 2016 2:00 pm

Re: Beovision 7102 CRT TV,schematic/advice please
 
You will have to setup the dynamic convergence, though. This was a one-time adjustment through plastic bars that were melted in place, so if necessary you will have to remove those and use rubber wedges.

zens.tv 6th Jun 2016 9:18 am

Re: Beovision 7102 CRT TV,schematic/advice please
 
hi Malc,scan coil connector joints ok

remember trying to set up convergence on sets,back in the day.what a nightmare.could never manage to align it spot on.


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