CP90 PYE 15” TV, no power led or picture. Buzzing sound

[Tvnoob007]

I have the above set that apparently uses the CP90 main board.

When I try and power it up it just makes a buzzing sound near the two transformers. I’ve checked the voltage at the 280v point and seems dc 320v. Moving forward I’m getting about 3v at the 19v and 95v points. Are these all dc voltages?

All fuses I’ve found so far seem intact.

[John123]

Hi, first try replacing the standby thyristor D6726.

[Tvnoob007]

Haven’t had a look at it yet, and don’t have a service manual for it, what part number is it and if I remove it can I test it?

Just checked the D6726 on google and one service pdf suggests this creates a loud buzz in standby. But my set doesn’t power up and the buzz isn’t that loud. Could it still be this part?

[1955APREN]

Hi
Just a few questions about your problem
1. Is this buzzing Sound coming through the speaker or is it vibration from one one the transformers.

2 Can you smell any thing getting hot .(Do not leave on for long)

My thoughts on this is that the line output transformer is short circuit.
with see switch off, measure the resistance from the collector of the line output transistor to chassis if this reads low disconnect the transistor and cheek the
resistance again, if still low the transformer is faulty.
Hope this might help
Derrick

[Tvnoob007]

Hello thanks for the info everyone.

The noise is from one of the transformers. I would say the larger one of the 2 in the power stage.

Can you tell me which part is the line output transistor?

I’ve only been turning it on for very short periods to test voltages, worried something will go bang.

Is it safe to touch any of the heat sinks etc while it’s on? I remember thinking I could touch the heat sink on a telephone system at work that stopped working, it made my arm buzz, was rather painful.

I don’t have a service manual or circuit diagram for this set yet so working blind a bit. I’ve got a DSO scope I’ve just bought and various soldering tools but I’m normally fixing 8 bit and 16 bit computers with it. So I’m a bit of a noob when it comes to TV’s.

This set is my own from the early 90’s and if upto my missus would have already been skipped.

[nigelr2000]

Circuit layout here https://elektrotanya.com/philips_ch_.../download.html

The line transistor will be one on a heat sink next to the line transformer (the one with wires coming out the top and 2 controls on the side) on the right hand side in this picture a BUT11

http://1.bp.blogspot.com/_SPwX1vYEKq...0/IMG_3033.JPG

[Heatercathodeshort]

From experience I would say that Derrick, rather unfortunately probably has the answer here. These particular grey series Philips LOPTs were a massive problem as they were also used in other manufacturers receivers.
I replaced huge numbers in Toshiba portable receivers that employed them. Toshiba LOPTs never failed and the general Philips components were also excellent but this series were seriously bad.
With a bit of luck it might be the LOP transistor as suggested. Well worth a try.
To be fair they were supplied at a very cheap price as they were aware of the problem.
Hope you get it working. They give a fantastic picture and the 15" version was also fitted in a B&O with a black screen filter. Was it really all that time ago? John.

[Sideband]

Originally Posted by Tvnoob007

Is it safe to touch any of the heat sinks etc while it’s on? I remember thinking I could touch the heat sink on a telephone system at work that stopped working, it made my arm buzz, was rather painful.

You have no experience of TV's....NO don't touch any heatsinks.....in fact I wouldn't recommend touching anything while the set is on. Besides what will touching the heatsinks tell you?

The main HT is 95 volts. The raw DC from the smoothing after the rectifier is about 320V. There is a plug near the line transformer that has a link on it. Pull that out and it will disconnect the line stage from the rest of the set. If you then measure 90V on the main HT rail then it's almost certainly the LOPT but worth checking the line O/P transistor first...you might be lucky.

I wrote a servicing article on this chassis in 1993 and it's here: https://www.americanradiohistory.com...on-1993-03.pdf

[Tvnoob007]

sorry if this is annoying for you guys, but looked at the schematics and some stuff seems repeated and I cant find the line transformer on there. I was going to make sure I was checking the transistor correctly. its like the whole HT bit is missing.

ive checked between the collector and ground and its near enough a dead short. about 6ohm I think.

cant find the plug yet. will do some googling to see if I can find a pic.

ok some progress. found the M6 connector and removed it.

now the buzzing has increased in pitch and I get 93v on one of the 95v marked points on the bottom of the board. the other 95v point which seems to run upto the LOPT only has about 8V.

should I try removing the transistor mentioned and see if I still have a short?

[nigelr2000]

yes worth a try but I think it's more likely the transformer, changed lots of them when I had a shop, nice little earner

[Tvnoob007]

If it is the transformer where’s best place to get one? Any particular brand?

Also if I fit a new transformer is it likely to be the only fault or could it have taken out other components?

And last question, if that fixes it are there any upgraded/service actions I should do on it. On old 8 bit computers I generally replace the electrolytic caps, not sure I want to replace this lot as there’s loads.

[Heatercathodeshort]

Sorry! I don't think you have enough experience to fault find on this chassis. The last thing you want is to spend money on a LOPT to find the fault is elsewhere on the circuit.
I doubt if any of the electrolytics on the CP90 would cause the fault described.
The LOPTs were obsolete years ago but there may still be a few available NOS but at a price.
The number of the LOPT required is on a small sticky label usually on the bottom [not underside] of the transformer. It may be something like AT2079/XXX. The number after the forward slash is most important and denotes the exact characteristics of the transformer that was used in many small screen receivers of the period.
Do not remove the transformer from the board without a desoldering pump! You will wreck the board.Maybe a Forum member near to you might offer to help but under the present circumstances...It's a long way from Lincolnshire to Horsham. Regards, John.

[Tvnoob007]

I've got a DE soldering station with vacuum gun plus a manual pump type so reckon I can get the tranny out easily. cant be any harder than recapping SMD stuff.

I will check the transistor first and see if its ok.

[Kyle__B]

The problem is the transformer will wick away a lot of heat but if you try to heat it up by holding the pump on then the track will come off the board along with it.

I like to put a little bit of new solder on top of the old one then do multiple goes with a braid to get rid of as much as possible before using the desoldering pump. Getting it all in one go is deffo the way to ruin it

[Tvnoob007]

Ok 20mins with me electric desoldering pump and the tranny is removed. Thought it was holding on somewhere for a minute then realise it had 2 plastic clips.

Before I removed it I tested between ground and the transistor collector with the transistor removed and got about 6ohms.

One question. Some of the replacement LOPT’s I’ve seen have the high voltage connector and that’s it. The other 2 wires going from the tube circuit board don’t appear to be sold with it. Do I have to remove these from the old LOPT? If so how don’t want to break something.

On the bottom of the LOPT looks like it says HO 8820. There’s a sticker on the side but it don’t look good, not sure I can get a code off it, says Phillips.

Hmm looks like 3692379/10 and bellow it 8825 possibly.

[Tvnoob007]

Ok after some google foo seems it’s been replaced by HR7503?

[Sideband]

8825 is the date code....25th week of 1988.

The leads....yes you will probably have to remove these from the old transformer....don't try just pulling them out, imagine they have a screw thread and twist them anticlockwise whilst gently pulling. They will come out quite cleanly. All you do is push them into the respective connectors on the new transformer. Check by gentle pulling that they are firmly gripped

[Tvnoob007]

Found a HR7503 for about £11 delivered. Got to be worth a punt?

[ben]

I also worked on dozens of these, they were great to resell as they had RCA input on the front. The line output transformer if grey original was usually u/s. The HRDiemen replacements were cheap and reliable.

From my notes, for future reference:
PHILIPS 15CE1210 CP90. FRAME COLLAPSE
-OPEN R3623 ( 8.2ohm) NR LOPTX CAUSE DRY JOINTS ALL OVER
DARK PIC AND AMNESIA
-REPLACE BACKUP BATT 2V4 110MAH

PHILIPS 21ce1251/16b CHASSIS CP90
WENT OFF WITH SMOKE/CRACKLING
-O/C BURNT PCB TRACES B+ LINE TO LOPTX PIN (5?) - REMAKE WITH WIRE.

PHILIPS 21ce1251/16b CP90
DEAD WHISTLING, PSU STARTS IF LINE STAGE DISCONNECTED, Line transistor OK.
-LOPTX PHILIPS 36923 = HR 7503, 12€

PHILIPS CP90 17"
NOT RESPONDING TO PANEL CONTROLS (EVEN WHEN CONNECTED DIRECTLY TO PINS 24-26 of uP)
-MICRO ?

PHILIPS 21CE1558 TXT. (NOTE: USES NEWER CP90 CHASSIS WITH LOTS MORE COMPONENTS ESP. PSU)
BLANK SCREEN RETRACE LINES NO SOUND
- D6733 BAV19 and 12v filter cap.
HERRINGBONE PATTERNING, MOIREE, AND VERT. TEARING ETC.
-CHANGE C2691 IN PSU (330Uf 35V)

NOTE: TO STORE PIC AND AUDIO SETTINGS: MAKE ADJUSTMENTS, THEN PRESS RHOMBUS STORE BUTTON (RECESSED) ON SET.

PHILPS 21CE1051 (CP90 NON REMOTE CHASSIS)
PICTURE TEARING, VERTICAL JITTER, FLAG WAVING - YOU NAME IT.
-IF board ICs overheated - changed all 1uF and 22uF caps but no improvement - changed entire IF sub board from scrap chassis, fault disappeared.

PHILIPS CP110
- BACKUP BATT 110 MAH 2.4V
AUDIO JAMMED ON FULL, CAN'T BE ALTERED ALSO BRILL COLOUR.
- front panel controls membrane u/s

philips 17ce1231/16r (cp90 chassis) .
Dead, no display, low volt supply appears to run.
-replace HT caps and wickman fuse in HT line

philips 17ce1231 and others as cp90.
no contrast/tinted pic
-replace the rear contrast pot-breaks off easily when opening and replacing rear cover TAKE CARE

philips 21ce1251/16b (cp90)
cuts out with whistle/ int. no switch on/ no standby etc.
-resolder LOPT pins

picture stretched at top; "egghead" symptoms
-replace all caps in vertical cct at rear of main pcb

PHILIPS 24CE3270/16B (cp110)
strobe effect: flash in picture every 2 seconds or so.
-replace transistor (T77 ) bc548 on crt pcb

[Tvnoob007]

Assuming once I fit this new LOPT it starts working, would i need to adjust the focus etc on the new LOPT? or do they some preset?