Repair tips for small CRT television?

Hello all,

The other day my old 16" CRT television died, and was wondering if anyone has repair tips for common / easy-to-find failures.

At the time it was hooked up to an old Sinclair ZX81 homecomputer, running a demo that did some funky things with the sync signals. I suspect that helped push this 10 year old TV over the edge - suddenly it said 'poof' and no image since... (black screen) :sad: But it might have been coincidence - this TV has seen countless work hours.

When powered on, I can hear a ticking sound (roughly once/second), and the standby/power LED flashes in same rhythm. But no sparks visible or anything like that.

I inspected insides carefully, there's no obvious burned parts, nothing smelling bad/melted, no blackened spots on circuit board, electrolytic capacitors all look fine. In fact, for a 10 year old TV the insides look relatively 'clean'... ;-) There's 1 main fuse, it's still okay. I can do some basic checks, like: low voltage supplies, spotted an NTC somewhere that looks like it's used as a fuse, bad solder contacts etc, but that's about it. Have only multimeter, no access to scope unfortunately. Also I have schematic (on paper), don't know if that's online anywhere.

I don't plan to invest much time/money into it as these things are considered near-worthless these days - people put them on roadside (still working sometimes), or free to pick up. It's just that right now an old CRT television is enough to cover my needs, and I don't like tossing 10+ kg. equipment if a $0,50 component replacement could fix it.

What is the Model number and the brand name of this TV? May help you.

It's a Grundig P 45-830 text

(=what it says on backside label)
Small/simple portable with SCART connector, bought in PAL country (Netherlands). Pretty much functioned without issues since I bought it (apart from remote control & a temporary loss of color it had some months ago).

When searching the 'net for schematic in .pdf format, there's talk of 'chassis type', I have no idea where to find that...

My first suspect would be the horizontal output transistor. The ticking sound indicates that the power supply is heavily overloaded and one of the most common culprits for that is a shorted H-out transistor. You probably killed it by driving the H-out section beyond its sync range.

Just confirm me the following:
Does it look like some what for the appearance:

And if you look at the PCB from components side does it look like (the Horizontal Transformer side):


Is the Horizontal transistor number is S2055 (if possible to look at).

Pjdd said:

My first suspect would be the horizontal output transistor. The ticking sound indicates that the power supply is heavily overloaded and one of the most common culprits for that is a shorted H-out transistor. You probably killed it by driving the H-out section beyond its sync range.

Click to expand...

Yeah that would sound like a reasonable explanation for the symptoms I was seeing.

Raza, thx very much for taking the time & look up details. :-D Board section shown looks like what I have (and component identifiers look the same too). Located that power transistor (T506), indeed says S2055 in schematic but "D1878" (= 2SD1878 I think) was mounted in that location. Datasheet specs are similar & same pinout. I just cut it out - nothing to loose here... :wink: After studying schematic concluded that it should be -reasonably- safe to power TV for a few seconds with that transistor removed. Result: clicking sound gone (figures, with horizontal coil & high-voltage primary side not driven), and power LED still flashing in same rhythm.

That power LED is driven from a 5V supply, which leaves a number of options open:

• Some part in / that uses 5V supply has died or is short-circuiting that.
• The 7805 that produces it has died. Unlikely (I've seen countless 7805's, some on their last legs but never a dead one), and then that 5V would probably be missing continuous.
• Primary side of transformer that produces these supply voltages, isn't driven anymore (or problem with feedback in that circuit). This would likely be a power FET or some hard-to-obtain control circuit.
• Some other option not yet checked.

I looked for similar power transistors in catalogs of some local shops, and they have little if any in this area (some high voltage some, high current many types, but not high voltage + high current, let alone exact type I'd need).

So I can see where this is going: spend much time, take educated guess, spend money & replace component - no cigar. Take next-best guess, spend more time & money, replace some other part - no cigar. Best outcome would be TV working & then dying again shortly after since it's an oldie already...

Therefore I've decided it's more time/cost-effective (for me) to just find a replacement & call this one a goner... I feel a bit sad about doing so, but as soon as simple/quick/easy/cheap doesn't apply anymore to fixing this 10 year old CRT, that's just how it is...

Thanks for your help & please don't waste anymore time on it... For the archives: last screenshot ever taken from it is here: **broken link removed** (and a ZX81 demo killed it, for an old CRT that's a stylish way to go, if you ask me :wink::lol

:-D Lovely decision. If you do afford to replace it that has no comparison as the time is more effective in other departments. If there is no High Voltage present this Blinking LED indicates it and the CPU locks the power to many circuits. If there is no input to 7805 then the main power circuit gone dead and if input is there and no out from 7805 meand it is gone. Any ways you decided to quit so me quit. As I have been repairing the TVs long time ago so I have many circuits still in my database. :smile: