More parts I need to replace on the VT100

[Gordon JC Pearce]

Tony Duell wrote:
>>>I find those sort of tips totally useless!. There could be many causes of 
>>>'no vertical deflection' (or whatever), the fact that _once_ it was 
>>>caused by a particular set of components doesn't mean it always is.
>>
>>I can't agree there.  When I used to repair TVs and video recorders and 
>>the like, I (like others) tended to find that different makes had their 
>>own particular favourite stock faults.
> 
> 
> If you run a reapir shop, I can see the use of them. Probably 90% of all 
> fauts are 'stock faults' and can be found in the database. It'll get 
> those units off the bench quickly. And I've heard of repair shops that 
> look for the stock faults and if it's something else, they return the 
> unit as being beyond repair (OUCH!).

Been there, done that.  Been the person they got returned to, as well...

> However, they seem to be a lot less use when it's a one-off unit which 
> you need to repair no matter what (like a classic computer). You're going 
> to have to do real fault diagnosis sometimes anyway, it doesn't make it 
> much more difficult to do it properly every time.

I'm sure that by now, if a stock fault was going to appear it would have 
done so by now.  In my experience they tend to be design problems more 
than anything else - like, oh for example, VT100 under-rated capacitors...


>>In that case, for example, if you got a Ferguson ICC9-chassis TV on the 
>>bench with no EW correction and excessive width, you'd go straight for a 
>>particular electrolytic somewhere around the scan drive circuit. 
>>Annoyingly enough I can't remember which one and my telly has just 
>>started doing that...
> 
> Alternatively you could get out he schematic, _understnad it_ and work 
> out what components could cause this problem.

If the schematic was available.  In any case it's a pretty bog standard 
EW modulator circuit - big electrolytic from the vertical scan circuit, 
pair of clamping diodes and their resistor, and another resistor to the 
width circuit.  It's just been so bloody long since I had one apart, and 
I don't fancy moving a 34" 4:3 telly...

Gordon