Sunn SR4150 schematic reqd

[blindboybenton]

Hi all

I have a sunn sr4150 with some burnt up resistors. I have a schematic for sr4150 "P " but this schematic uses TIP142/147 on the outputs and Mine uses Tip102/107 and totally different layout on the board. I have never done one before and i don't know how many versions

can anyone Help

BBB

[Enzo]

That is what the P on the end means - it is a different model from your plain 4150.


I looked on my discs and in my paper files, and as a Fender/Sunn service center the last three decades, I have only the SR4150P.


CONTACT Fender and ask them if they have it in their files. Include your serial number if you have one on it, that might help them identify the thing. it is possible the same power amp board as used in other models, but I do not recall those transistors in use.


TIP 102/107 are darlingtons just as the TIP142/147 are. The 142 is a 12A part and the 102 is an 8A part. I suspect the two circuits are fairly similar under the skin.

[Jazz P Bass]

I, for one, find it odd that they would use a TO220 device for an output transistor.

[blindboybenton]

Many thanks Enzo. Looking at the component layout for the " P " version its different and all the component refs are not matching. Ive fixed it once and was using it in the workshop and connected an old power amp to the monitor out and it went bang again. Had been using it for about 3 months since the the repair.

BBB

[blindboybenton]

Well i can asure you that its correct. 3 x Tip107 and 3 x Tip102. I brought the amp faulty to use in workshop or sell and the output transistors had never been changed

BBB

[Jazz P Bass]

It would be awfully obvious if a TO220 was mounted in a TO218 pin spacing.

I was simply stating that it is odd.

[blindboybenton]

It would be awfully obvious if a TO220 was mounted in a TO218 pin spacing.

I was simply stating that it is odd.

Nothing awfully obivious about it ... The SR4150P Schematic i have shows the amp with 2 x tip142 and 2 x tip147. This amp is using 3 x tip107 and 3 x tip102. The circuit board does not allow me to use tip142/147. On the schematic it shows a picture layout of the components and its different to my one. On the front panel it states its a SR4150. If i get any luck out of fender getting schematic. I will post it up

bbb

[Enzo]

What Jazz was saying was that if someone had put TO220s where TO218s belong THAT would be obvious to the eye.

No one is doubting you have what you have, just reporting that it is very unusual.


What I mentioned earlier was that I would wager the circuits you have and the newer TIP142 one are very similar. I understand the layout would be different and the part numbers different, but that doesn't mean we can;t get insight from the newer schematic.

[blindboybenton]

Hi All

Ive had a reply from Fender uk. All they have is a Parts list. I will waiting to see if fender usa can come up with the goods
output.pdf

[blindboybenton]

Hi all

Just had a reply from fender uk. I was emailed this. Maybe its worth keeping this schematic in your records. as its been a topic on conversation
SR-4150 (SX-4150).pdf

[Enzo]

Hey, thanks!!

It turns out I have that in my files, just no schematic per se. It never occurred to me to scan the service bulletins. I wrongly assumed all of those would refer to schematics already on file. Now I am going to cross reference my service bulletins in the schematic index.

[blackba]

Hi all

Just had a reply from fender uk. I was emailed this. Maybe its worth keeping this schematic in your records. as its been a topic on conversation
[ATTACH]27211[/ATTACH]

Sorry to dig up an old thread, but I noticed in the attachment that there is a change to improve thermal stability and that 20 resistors need to be changed, but the list appears to be cut off. I checked the amp I have in for repair and all are the old value. Do you happen to have the rest of the first page for the technical service bulletin?

This amp is in for blowing the fast blow 6A fuses. So far no easy signs, other than the amp has been worked on before.

[blindboybenton]

Ive checked that is all i have on this amp

[Enzo]

There may be a thermal stability update, but that isn't the cause of your fuse blows. First thing to check is for shorted output transistors, and after that look for shorted main rectifiers. Those are most common cause of blowing fuses in solid state amps.

[J M Fahey]

We can reason what was behind the changes we know and try to deduce the unknowns.

1) as a cheap manufacturer (aren't we all?) I can understand the TO220 power transistor choice.
I once made a 30/40W amp which was a commercial failure (too large for home, too small for live use) and I got stuck with 200 pairs of TIP122/127 .
Would I eat them? .... no way !!!!
Designed a new 100W board using 2 x TO220 pairs instead of a pair TIP142/147 ..... sold like hot cakes.
As Enzo suggests, the rest of the amp was exactly the same.
Which also means: put both versions side by side (TO220 and TO218) , probably the new one has the new values
Or not, but it takes only a few minutes.
In fact, post the new one here so we all can see it.

2) let's see what the suggestions are and what logic might be behind them:

a) R3-R4 from 150r 5W to 330r 5W
they are in series with +/- 15V regulators Q1 and Q2 .
They were probably cooking them, increased series resistors take some of the thermal load on themselves.
So far, so good, huh?

I'd guess that a thermal improvement mod *should* mess with biasing, so
b) R12 : 22k>3k huh? , it's already 3k on the schematic !!!! another case of "the right hand does not know what the left one is doing?"

c) R17 22k>120K AGAIN already updated in the schematic ...not necessarily on the PCB, please recheck.

d) R18 1k>1k2 AGAIN already updated in the schematic ...not necessarily on the PCB, please recheck.

from what I see here, mods are already on the schematic (they might have edited it in a later revision and forgot to update the Mod or considered that some Service guy MIGHT find a very early one so left it just in case) .

So I suggest you check which one you actually have and anyway check it against a known good later one.

The few Mods I see (those 5 resistors) make life easier for regulators and mod bias some short circuit protection values, so lost ones might do something similar.
Bias seems to be covered and is the single most important of them.

In any case, not *drastic* changes.

As a general cure all patent medicine , I'd bias them real cold, even, say, 1 mA`, drive the amp hard (1 hour at, say, 60/80% full power into the minimum load) until heatsinks are unbearably hot and recheck they didn't thermally runaway (rise idle current to, say, 15 or 30mA or more on their own).

I have sold underbiased amps for ages (Peavey was famous for that) , and almost nobody complains or even notices.

Not everybody plays Classical Piano patches, alone, at bedroom level.