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Old 18th May 2020, 9:12 pm   #61
staticmind
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Default Re: B&O Capri 606 TV (17") restoration

PCL84 measurements - forget my previous post about the close to 0V measurement at pin 3:
Pin 1: 146.3V
Pin 2: 4.16V
Pin 3: 5.72V
Pin 4: 109V
Pin 7: 5.23V
Pin 8: 0.06V
Pin 9: 0.0V.

The Pin 2 (g1) is approximately the same voltage as on the wiper of the contrast pot.

A good thing is that I have a very dark raster. As in very dark with just the slightest amount of snow visible. Brightness control has been set midway for all measurements. Not sure how it should be set as it isn't mentioned anywhere.

Component 63 measures 1.6 ohm, so it is fine presumeably. The RL41 diode in the RF can 971H97 measures about 0.3V in the correct direction... about 1.1V in the other direction. Not sure if that is correct - the meter is a fluke 73, by the way.
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Old 18th May 2020, 10:38 pm   #62
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Default Re: B&O Capri 606 TV (17") restoration

the paralelled resistor was probably to increase brightness you are right..
if the grid of the tube is at 0v, and 15v is specified at the schematic than i would expect that tube to not conduct due to a lack of bias, that would explain all the symptoms, focus yourself on the dc path from b+ to grid of the tube, i dont see how the tuner can affect that but i will look again at the schematic. only thing possible would be some problem in the agc, IF the AGC acts on the video amp (on some sets it does) i have to look again at the schematic

the cathode of the pcl84 measuring low means either cathode resistor gone high or the tube not conducting enough, most likely second option due to lack of grid bias

explain better to me what you mean by measuring the otput of the tuner, were did you measure and how?

you say this:
The Pin 2 (g1) is approximately the same voltage as on the wiper of the contrast pot.
so the prime suspect is the 1.8m resistor before the pot, check that ASAP


the didoe rl41 that you mention is the video detector, probably a germanium, should read 300mv forward like you said but dont bother with it because from the wiper of the contrast pot to g1 of video amp there is a dc path that doesnt have to go through the diode so BIAS voltage should be there regardless of the diode condition. that dc path is 65 - 66 - 67 and then to the contrast pot

67 should also be checked and the 1n decoulpling cap (68) checked for leakage/short or cutted off temporarily

if all above fails try disconnecting component 69
do all of this and it has to work

Last edited by PortugalTV; 18th May 2020 at 10:58 pm.
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Old 19th May 2020, 8:06 pm   #63
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Default Re: B&O Capri 606 TV (17") restoration

Hi again,
It was a mistake that g1 was 0V, it is as stated in my previous post 4.16V. Didn't get to edit the post, when it was possible. I might have swapped the conventional way of counting pins, so the numbers might be in reverse order. Yes, it is supposed to be 15.5V, so I agree the problem must be lack of bias.

As I see it, the AGC involves the video stage, namely it is taken from the plate of the triode section of PCL84. I'm not sure exactly how it works, as it seems to also connect to the LOPTx after the 0.22uF capacitor. As mentioned the LOPTx section has been somewhat modified to accommodate a different (newer) one.
The AGC is then fed back to the tuner and the image IF stage.

67 measures 2.91 kOhm, and the 68 measures 1n. So they seem fine. I measured 37 and 36 too, they are spot on.

Going along those lines, I will measure 47, 48 and 50 Thursday - and the 150pF in the horizontal deflection going to the AGC. I'll also check the 1MOhm resistors before the 2MOhm AGC pot.

The tuner output I measured on the connection going to the Image IF stage, RF circuit 971H96. Multimeter on resistance mode, one probe on the chassis of the tuner, another probe on the (center) conductor/connection to the Image IF stage. This measures 0 ohms, but I am not sure if it is supposed to be that, but as I see it the 820pF capacitor between the two coils should block any DC path to ground. Do you agree?
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Old 19th May 2020, 10:19 pm   #64
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Default Re: B&O Capri 606 TV (17") restoration

Hi
tube pins are always counted clockwise viewed from the bottom and anti clockwise from the top. counting starts at the place were there is a gap between pins,on some bases there is a notch etc, this is valid for crts also and any pin base you can imagine
i have some tube socket test adapters i made to test tubes from the upper side with the tv turned on,they are very helpfull you could make or buy one, i can post a picture if you want to make one

the agc "comes" from the video amp, simplifying it , it takes black level and the more black the pictue has the more negative it goes, and as you know putting negative voltage on g1 of tubes lowers the gain. they inject that negative voltage on the IF and tuner, sometimes on the video amp. then you have a reservoir cap that provides a "time buffer"so the agc does not jump around fast on different scenes in a movie for example. on your set it does not seem to act on the video amp itself but i might be wrong. you can always disconnect the agc for maximum gain on any set but it often overloads and you loose sync etc

on some sets the reason the agc circuit is tied to the flyback is to obtain some ac, then its chopped to get a negative voltage, that voltage is then regulated by a tube depending on black level and there is your agc
i have a set were they get that negative voltage from the ac on the filament string at a certain point, every maker and model has a different setup


about the tuner, if you have zero ohms from that point to chassis DEFINETELY you have a short there. maybe a coil is shorted against a the tuner chassis or inside 971h96 metal can maybe? maybe
also shielded cables often short on old tv's, had that problem many times but never in the IF/tuner but always on the horizontal stage because the high pulses heat up the wire and it gets brittle, anyway the short has to be checked and cleared

with that short you will definetely loose any signal but you should be able to inject a signal at the video amp and get it dispplayed.i would try removing the detector diode and inject a signal at the grid of the tube via a coupling capacitor. use composite video form a dvd.

maybe the short creates a black picture and the agc blocks the gain of the video amp? have to study better the schematic, i only glanced at it. with that short i would expect a blank raster but that depends how they designed the circuitry. it would be great if other people also gave their insight, they might more skilled than i.

if your tuner uses a rotating drum they dont be afraid its very easy to take apart and service. just dont move any components around or you will mess up the alignment just by changing the component position. the shortshould be easy to find. often there are some ceramic tube insulators and a wire is run on the inside between different sections on the tuner. its not uncommon for the ceramic to break and thewire to short to gnd when wiggling the tubes around too hard

Last edited by PortugalTV; 19th May 2020 at 10:46 pm.
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Old 19th May 2020, 10:50 pm   #65
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Default Re: B&O Capri 606 TV (17") restoration

after clearing the short try disconnecting capacitor 69. its the only way i can see for the agc to act on the contrast/video amp gain

i was writing as i was thinking so ignore any repeated things etc

Last edited by PortugalTV; 19th May 2020 at 10:56 pm.
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Old 20th May 2020, 10:30 pm   #66
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Default Re: B&O Capri 606 TV (17") restoration

As always, thank you very much for the insight on this. The AGC functionality makes sense.

I stumbled upon this site with an unbelievable amount of information Philips tuners:
https://www.maximus-randd.com/tv-tuner-history-pt1.html

My TV has an Philips AT7432 tuner. The schematic of it is also shown on the site as: https://www.maximus-randd.com/upload...uit_1_orig.jpg

Here it shows that there's a coil at the IF output going to ground. But in the TV's schematics I don't see that the coil is connected to ground - it is in series with the output, or am I interpreting this wrong? If there's a coil going to ground, it seems correct that I'm measuring 0 ohms, provided the coil has few turns.

The tuner is a rotating drum type with coils etched on multiple (10) PCBs. It was easy to take apart and reassemble.
The only thing I changed in the tuner was a few resistors that measured more than 15% out of tolerance, and then one crusty 820p cap. I still have the old components, in case it messes with the alignment. There are a couple of screws on the tuner chassis with loctite or paint. I know they are for alignment, so didn't touch anything here at all. The replacement resistors follow the same path, completely.

You're also right about the wire going between tuner sections. Thinnest layer of enameled wire I've ever seen, will investigate if there are any shorts here as well. I'll also get to check the shielded cable and 971H96.
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Old 20th May 2020, 11:04 pm   #67
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Default Re: B&O Capri 606 TV (17") restoration

Correction: I have an AT7632 tuner.
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Old 21st May 2020, 12:33 am   #68
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Default Re: B&O Capri 606 TV (17") restoration

i am printing that website about tuners as bedside reading

definetely keep the old cap! a tv with tuner or IF out of alignment is useless. on your schematic there is no dc path to ground,could be a different revision of the tuner or a misprint, investigate that and let us know.

good luck
Hugo
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Old 21st May 2020, 9:15 pm   #69
staticmind
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Default Re: B&O Capri 606 TV (17") restoration

Thanks Hugo. If you have trouble falling asleep, I'm sure that it will help reading

My tuner matches that of the website, not the B&O schematic.
There is no damage or shorts to be identified inside the tuner. I did not change back the few resistors I replaced yet, but will remember to do that, for now that is not the main issue.

Trying my (borrowed) Fluke 175 instead, I measure 0.5 ohms to ground at the IF output of the tuner.

I measured the components that I mentioned in my previous post and found no problems - my Fluke 175 does not measure caps below 1n, so for the 150p and similar small caps I just measured it wasn't shorted.
Everything is fine inside the 971H96 tin as well.

Before experimenting with disconnecting the AGC impact on the video section as you suggested, my mind is still bugged by the fact that the b+ voltage is as low as it is. So I'm thinking I have damaged the selenium recitifier by for a split second having overloaded/shorted the output by tampering with the tubes as I did. So my next plan is to use a high current rating diode and a 20W dropper/power resistor (15 ohm should do), and ensure that b+ is as it should be. I will be quick to turn off the set if the cathode voltage becomes excessive.
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Old 22nd May 2020, 10:20 pm   #70
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Default Re: B&O Capri 606 TV (17") restoration

Ok with an 1N4007 and a 15 Ohm dropper, I have about 180V on b+, but it didn't solve anything, as you also suggested much earlier.

Disconnecting C69 did nothing to the voltages. It might be my hearing, but when it is disconnected I don't hear the line whistle.

I did measure out voltages of the 3x EF80 in the image IF section, they seem about right. As I have no signal integrity to worry about, the most important measurements would be from the last EF80 (no 3.). On the anode, I have about 185V.

I have spent some hours analysing the "output stage" of the image IF, and how it affects g1 of PCL84.

In the 971H97, only AC is coupled by a coil/transformer, so the anode voltage passes through the coil and 10 kOhm resistor to g2, so I actually don't see how it can affect g1 of PCL84.

As I see it, the ONLY way to affect g1 of PCL84 is by voltage rail +a, going through the 1.8M resistor to the pot, then through resistor 67, the combined resistor/coil 66, then to can 971H77, where it goes to resistor/coil 65 and then to g1 of PCL84.

However, in 971H77, it also passes to resistor/coil 63 and down into 971H97 and forwarded through the video detector diode RL41.

When I measured RL41 last time, I did detect the correct forward voltage, but also a higher voltage when measured in the opposite direction. What bugs me about this is that if the diode conducts in the other direction to, DC can pass through "backwards" though the circuit if you know what I mean.
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Old 27th May 2020, 12:38 am   #71
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Default Re: B&O Capri 606 TV (17") restoration

Most tv techs would just put a diode without any dropper and it would work just fine. i would suggest you also do that for testing and choose your resistor in the end when it all works fine. the circuit will work just ok on all tube sets even with 20% more or less b+ than specified

edit: i see you already done that!

you mention that sometimes you dont hear line whistle. so we can be looking at the wrong part of the circuit. can you check if the high voltage goes away? i use a screwdriver , some people are afraid of that and i respect it but really catching a cold is more frightneing than that so...can you check the presence of eht? insulated screwdriver and approach it to the cap of the eht rectifier. should get a steady purple arc. dont worry unless you have severe heart problems, if it bites you its just a zap like those electric chinese fly swatters

Last edited by PortugalTV; 27th May 2020 at 12:46 am.
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Old 27th May 2020, 12:50 am   #72
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Default Re: B&O Capri 606 TV (17") restoration

"In the 971H97, only AC is coupled by a coil/transformer, so the anode voltage passes through the coil and 10 kOhm resistor to g2, so I actually don't see how it can affect g1 of PCL84."

no no...g2 is directly tied to B supply, no components in the way. g1 is the one next to the cathode, the first grid counting from the bottom of the drawing

g1 is the one that gets voltage from the wiper of contrast pot via coils / resistors. along with that dc voltage it receives the ac video signal.

you can try disconnecting the cathode of crt and short it to ground. you should get a blank super bright raster if everything else is OK. (eht and deflection)

"When I measured RL41 last time, I did detect the correct forward voltage, but also a higher voltage when measured in the opposite direction. What bugs me about this is that if the diode conducts in the other direction to, DC can pass through "backwards" though the circuit if you know what I mean."
GErmanium diodes and transistors often have that type of reverse leakage and yet they are good. But the only way to be certain is a replacement germanium fast diode. On some occasions i tried silicon replacements as video detectors and they did not work at all.

you can and should try to disconnect the wire on the wiper of contrast pot, then shunt the wiper to the grid of the video amplifier tube. Now via a capacitor inject a video signal there. you should see it on the screen. use an old dvd or anything that outputs composite video. if its a metal case dvd, the body of the dvd will be at chassis potential so dont touch it. its easy and will prove if the problem is ahead or before the video amp.
a high value film cap like 100nf or anything you have at hand should work fine. just to keep the dc off of your video dvd device. dont forget to connect the video ground to chassis of the tv. (carefull with shocks)

another word about high voltage,if you suspect high voltage and line whistle is going away you can check if the oscillator is working by checking the grid of the horizontal output valve with a dmm
if the oscillator is working there should be around -30 to -50v depending of the circuit and valve it uses. no negative voltage there means no pulse from the oscillator and that will kill the ouput valve very fast (redplating)
you can also connect a scope there for fun. you should see a sort of sawtooth waveform. rises slowly, stays at the top for a while then falls very steeply. that's around 15khz

Last edited by PortugalTV; 27th May 2020 at 1:11 am.
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Old 27th May 2020, 8:53 pm   #73
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Default Re: B&O Capri 606 TV (17") restoration

You're of course right about 971H97 ang g1 of PCL84, don't know how to actually interpret my last post to be honest.

So going by calculations, the DC at g1 is given by the voltage division by the contrast pot + the 1.8M resistor and the 4.7k to ground. With +a being 200V, this should be around 5.9V max at g1, when the contrast pot is at max. As my 1.8M resistor measures about 2 Mohm, the voltage is closer to 5V.

I thus don't see how they're ever able to get 15.5V at g1 of PCL84. It shouldn't be possible? Or does white noise from the tuner create a DC offset as well due to the video detector diode circuit?

I lifted one leg of the RL41 and measured again. A forward drop of 0.293V and nothing in reverse. Perhaps one of the 6pF caps are not as good as they should be, as this is the only way I can see a "leak". But I don't think this can be the cause of my troubles.

I'll try to find an old DVD player or similar with composite output - I think I'll have to ask around. I use the TV with a variac, which is also an isolation transformer type.
But firstly I might want to check the rest of the sections and check the tube voltages (of course not the top caps of PY88, PL36, DY87....). G1 of PL36 is stated to measure -49Vdc, so let's see.

I measured the voltages at the CRT socket as well. G2 measured nearly 500V, but drops quickly as I was measuring. So that's terrible. I will try to draw up a schematic of how the modifications were made with the AT2021 LOPTx.

By the way, I collected a Capri 606, but in 21" as well. Components look much less tired so that set was retired relatively early. This is so that I have a backup source of special components and the tuner unit. The LOPTx is not the AT2016 either, but an AT2018. The durability of that AT2016 must have been downright awful.
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Old 27th May 2020, 9:39 pm   #74
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Default Re: B&O Capri 606 TV (17") restoration

Hi,
I didn't notice this thread until today.
It's quite interesting to follow the process of getting this oldie going again
You're doing exactly what I did on a daily basis in the early 70'ies working as an apprentice to become a TV/Radio repair tech.
Anyway, what I want to say is that I'm about 35~40Km to the south of Aalborg and I have every valve/tube NOS for this TV, possibly except the DY87.
I haven't yet found any reason to stock that one except for renovating old B/W TV's which I don't do.
One or two MAY have slipped in though.
I have valve-testers on hand and so can easily check the valves you already have, as well as offer you to borrow what NOS valves you feel may need to complete the repair-job.
As I remeber it, with no signal-input to the antenna-socket, the lack of snow/noise in the picture often pointed to a fault in the IF-amplifier circuits. Most likely the EF80 valves would go low on amplification leaving a bleak picture with severe loss of contrast.

Best regards,

/Torben
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Old 27th May 2020, 10:40 pm   #75
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Default Re: B&O Capri 606 TV (17") restoration

"So going by calculations, the DC at g1 is given by the voltage division by the contrast pot + the 1.8M resistor and the 4.7k to ground. With +a being 200V, this should be around 5.9V max at g1, when the contrast pot is at max. As my 1.8M resistor measures about 2 Mohm, the voltage is closer to 5V."

Hi again! the voltage will fluctuate depending on how much current is pulled by the tube's grid...its not just a matter of dividing voltage.....lets say you have a 200v b+ and then a 10meg resistor and nothing after the resistor...if you probe after the 10 meg resistor you will get FULL 200v because the DMM does not pull almost any current so no voltage is dropped across the resistor...hope it makes sense, if not let me know..

i would avoid headache and stick with the schematic's figures.
i dont believe the snow from the tuner will create dc offset. on sets that dont use grid bias (grid is at 0v and contrast pot acts on the cathode of video amp)the dc level at the grid of the video amp is zero with or without signal

you really should try to inject composite...any thing will do....cable tv box, playstation, dvd player, etc etc etc
or just ground the cathode of the crt

dont give up you already put much time on this one we want to see it alive

Last edited by PortugalTV; 27th May 2020 at 10:49 pm.
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Old 18th Aug 2020, 6:49 pm   #76
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Default Re: B&O Capri 606 TV (17") restoration

Hi Tri-comp/Torben,

Sorry, didn't pay more attention to new posts, as I had and still have more important things to do (work), so not much time available to work on the Capri. Sounds really interesting about working as an apprentice in the 70'ies. I wish I knew that you had all the required tubes - already bought an extra set.


One thing I noticed about the AW43-88 heater is that it glows extra bright while the set warms up. It did not do that before while the set did show a raster.
I also got myself a Müter BMR7 CRT tester with the appropriate adaptor.
The BMR7 also allows connection of an amperemeter to measure the filament current draw, and I have some bad news: It draws about 600 mA at 6.3V instead of 300 mA, and glows brightly.
The CRT of the 21" Capri (AW53-88) draws 290 mA at 6.3V and glows normally, as the AW43-88 used to do.
The BMR7 does not report any shorts on the AW43-88 (or the AW53-88).
Can the filament suddenly become half the resistance? Is this a known issue?
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Old 1st Sep 2020, 3:46 pm   #77
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Default Re: B&O Capri 606 TV (17") restoration

NO!
But the AW 53-88 and the AW 43-88 are the same CRTs, seen by the technical view.
If you are commen with TV sets, it will be possible to run the AW 43-88,
the trouble maker, with the working TV!
If you place both sets back to back, the wires has to be long enough.
The deflection yoke and all the massa conections (outside crt coating!) has
to be connected in the same way as the "own" tube of the working set.
For safety reasons use the original deflection yoke of the working set, the plugs might be the same, but
the inner connections will be different!
The high voltage cable will be long enough, mostly they are much longer and
rolled and mounted on the cage (Philips line output transformers).

If that kind of construction is possible, you will have a very safe view on that, what is really going
on with the CRT which you don´t like to trust.

ALL THIS HAS TO BE DONE WITH CARE!!!!!!!!!!! Remember that there will be HV at the HV plug, even
the TV is switched off since a while!!!!!!!!!!!!!!!!!!!!!!!

Good luck!
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MARC BOLAN, he was/is the real king of Pop Music!
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Old 17th Sep 2020, 5:56 pm   #78
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Default Re: B&O Capri 606 TV (17") restoration

Hi German Dalek,

Thank you for the advice. I succeeded with connecting the AW53-88 up to the other chassis. The same bright raster is shown, and the voltages are identical and still much too high. About 120V on the cathode!
I will perform more measurements, but that will be with the other non-working AW43-88 connected instead.

Using a Müter BMR7, both CRTs measure about the same in emission (low/poor), but the brightness of the two CRTs (when the AW43-88 worked) is about the same. This leads me to conclude that the voltages have been off all the time, especially G1 and G2. G2 is for example around 500V!

The AW53-88 based Capri has much less use and the PCBs basically look like new, also behind the sockets. As the cabinet is in pretty poor condition, my plan is to replace the electrolytics and film caps and move it to the 17" Capri cabinet.

I'll need a new (old) working AW43-88. Luckily, they are not so rare a find at least in the Netherlands and Germany, but in Denmark, I'm probably 40 years too late. I found an untested Telefunken AW43-88 in Germany, but with missing scan coils. It seems from the data sheets that the Philips AW43-88 scan coils can be used without any issue as the curvatures seem to be very close.
In order to fit a new CRT I'll have to remove the support band that goes around the edge of the CRT, and I'm actually a bit terrified thinking of doing that, as I understand it the CRT has no built in implosion protection. Is the purpose of this band to add any protection to the CRT at all or is it just to add holes and standoffs for fixing the CRT to the cabinet? Back in the days, did service technicians need to re-use the band as the CRT was delivered without one?
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