It should read, ‘The Samson Success Story-Never Give a Sucker an Even Break’….but I couldn’t fit it all on.
Once upon a time (yes, you can put on your bedsocks and the nightcap with the nice bobble on it)….once upon a time, people who made things used to have a concern about their being able to get them fixed when they burst into flame, or what have you. At the times we are considering, laudable manufacturers of the quality of Leak, Quad, Radford, Mullard, (and Fender and Gibson and Ampeg and Selmer and on, and on) would credit their customers with a bit of sense and supply a schematic diagram with their hard earned purchase. Some would even stick the diagram in the amp somewhere.
Nowadays, of course, the gear is much more complicated. And also, it’s much more complicated. Apart from that it’s much more complicated. And also, well, it’s much more complicated. Don’t ask me why, though. Anyway, because it’s so much MORE COMPLICATED, the poor stupid cretins like us (who were after all, daft enough to buy the stuff in the first place) shouldn’t be allowed the temptation to want to get it fixed. So, these days, not only will you be unlikely to find a schematic diagram supplied, you’ll be lucky to find one on the same planet. Because, obviously, it’s far TOO COMPLICATED.
The last bulletin on the Samson 308i had me tearing my hair out and donating it to the cushion manufacturing cottage industry. They would be thin cushions, I’ll admit that. I didn’t fix it. I’ll admit that as well. BUT.
I assembled 61 data sheets, drawings, specs, sketches. I also drew out a significant chunk of the circuit. All this took a long time, my only motive being bloody mindedness. I love the idea that the people who make these things take responsibility for their doings. It doesn’t seem to happen very often currently. Probably too clever, eh?
Here’s an aside, and a plug for Marshall, as it happens. A gent called Simon wanted me to take a look at hand wired 20 watt head that had faulted. He’d paid something of the order £1700 for it. (Yes I got the noughts right). The mains transformer had blown, I gave it him back and told him to get in touch with Marshall, because it was a bit over warranty, but not much. They shipped it free of charge, and repaired it in the week. Hat’s off to those gents (and ladies). I ran up a flag to mark the occasion.
Anyway, back to Samson, who I don’t run up flags for.
The result of all this delving (which would have taken me half an hour with the schematic) was to show up the fact that there are two other devices in there (other than the main Fairchild switchmode chip) that supply the low voltage regulators for the preamps and 5volt digital supplies. One is a TNY274-280 off-line switching chip, and the other is a Viper 28 which is a pulse width modulator chip.
I replaced these and all the original repairs I did to the main switching STARTED WORKING!!!!!
Walla! Fixed! I assumed from this that the low voltage power supplies enabled the high voltage/current stuff and therefore nothing worked until they were all happy.
Unfortunately, this will not help you to fix one yourself. They are bad news to work on with everything surface mount and very small.
But it just shows that you can crack these codes if you are bloody minded enough.
Time for tea.