Fender Deluxe 85 weird resistor value.

soniccustard · Post by **soniccustard** » 18 May 2012, 11:07

Hey, been lurking and reading for a long time but this is my first post!

I have a Fender Deluxe 85 that died on me (mid gig at the HMV Forum of all places!) and it turns out that two resistors have blown in it. Not too big of a problem except that they're 290ohm 5w resistors and I can't find replacements anywhere.

Does anyone have any idea where I can find them? Already tried Rapid, Maplin and Bitsbox, none of them have anything even close.

Thanks for your help!

Seiche · Post by **Seiche** » 18 May 2012, 14:28

to get an exact 290ohm:
2 of these and 1 of these in parallel with each other

soniccustard · Post by **soniccustard** » 18 May 2012, 15:16

You reckon that'll work? On reading the resistors one comes up as 232 and other one 234, I'm guessing that's just from them being old. I think if possible I'd like to find the correct value so I don't have load of extra bits in there, more things to go wrong, haha!

Edit - Looking at it the solder is totally burned out, but the actual components are fine, I'll try just re-soldering them at first. I've actually bought a Fender 85 that I'm picking up tomorrow as a replacement, once I've fixed the Deluxe I'll have a nice little stereo setup

.

phibes · Post by **phibes** » 18 May 2012, 16:01

Where are you located?

You might wanna figure out why that part of the amp is frying before replacing parts. She solid state?

soniccustard · Post by **soniccustard** » 18 May 2012, 22:44

I'm in the UK, the UK version of the amp has a different power supply section to the US version. The parts that have burned are R115 and R116, I have no idea how it happened, I've been using it for about 18 months doings lots of shows, recording and rehearsal, so probably just wear and tear.

I did read on another forum (I can't find the link now) that this exact thing has happened to other people's Deluxe 85s, the resistors form part of a voltage divider.

It is solid state, yup.

deltafred · Post by **deltafred** » 18 May 2012, 23:03

phibes wrote:
You might wanna figure out why that part of the amp is frying before replacing parts. She solid state?

Looking at http://www.scribd.com/repartout/d/27558 ... -Deluxe-85 R115 and R116 are given as 240 ohms and are in the power supply so chances are something else is causing them to blow.

As a WAG I would look at the output transistors after replacing R115 & R116 and before switching back on. (TIP142, TIP147 power darlingtons)

soniccustard · Post by **soniccustard** » 18 May 2012, 23:41

That parts list is very handy, the schematic Fender sent me is the one from that page, it's drawn in pen and it's really hard to read. 240 ohms sure makes a lot more sense.

deltafred · Post by **deltafred** » 19 May 2012, 00:11

soniccustard wrote:That parts list is very handy, the schematic Fender sent me is the one from that page, it's drawn in pen and it's really hard to read. 240 ohms sure makes a lot more sense.

Yea, you have to guess quite a bit with that schematic.

DrNomis · Post by **DrNomis** » 19 May 2012, 01:38

If you want, you could try ordering a couple of 270 Ohm/5 Watt resistors from Jaycar Electronics, the Cat. No. is RR-3284 and the price is Au $0.40 each, you can order them online from this website:

http://www.jaycar.com/splash.html

deltafred · Post by **deltafred** » 19 May 2012, 08:20

deltafred wrote: As a WAG I would look at the output transistors after replacing R115 & R116 and before switching back on. (TIP142, TIP147 power darlingtons)

Ignore the above as looking again they are in the dropper chain for the +/- 15v etc for the preamp.

soniccustard · Post by **soniccustard** » 19 May 2012, 10:24

Thanks for the help so far, I'll have to get on it next week now as I'm doing a show over the weekend, but the 270 ohm idea looks like a good one!

soniccustard · Post by **soniccustard** » 19 May 2012, 11:09

I just found these - correct value, cemented so they're exactly the same as the ones in there already, should I grab these?

http://www.ebay.co.uk/itm/10pcs-Ceramic ... 742wt_1180

phatt · Post by **phatt** » 19 May 2012, 11:20

My best guess;

The issue is not so much a cheap design flaw but more about the scam of saving the planet morons who want everything to be NICE and fit into their idealistic mind set. The manufacturers don't mind because *Lead* is not cheap ,, so great they save a few more dollars on cost!! Yeah pull the other leg. LOL

I'm guessing The two resistors (See pic) run hot and with *RoHS* firmly in place,,means No Lead in Solder allowed and hence the tin crap cheap stuff just cracks ,,, instant cold solder joint. YES Under extreme heat it will Vaporize

Solder with no *Lead* is like an Engine with no oil??
Sure it will go at first but soon you will have trouble with it!!!

Heck most military people would shot a designer who uses lead free solder. My guess,,Lead free solder is the number one reason for modern circuit board failures.

Yes just resolder the joints with leaded solder and it will work.

If you want your RoHS gear to last go find all the places on the board that have warm to hot running components and resolder those traces with LEAD solder and you will help keep it alive a lot longer and while inside lift all hot running devices away from the board.

*IF*? the traces are badly burned then consider doubling the wattage of those R's (if 5watt? then try 10 watts) and mount them well away from the board so that the heat does not destroy the traces over time.

Ceramic resistors are designed to run hot, Hot enough to burn on touching BUT without the LEAD solder joins will crack prematurely. If I had a dollar for every Amp that failed because of this I'd be rich.

Value is not super critical I use 330 too 470 Ohms 10 Watt in those type amps. Depends on the circuit and voltages present you will have to suck it a see.
42 VDC down to 16 VDC is a fair big wack so bigger wattage and bigger value is likely needed. Try 470 R and see if the 16VDC rails stay stable ,, if not drop back to 330 R.
My bet,,, 270 R is way to low for the 42VDC which puts the 16V Zener diodes under more stress.

Some 4 years ago my mate had a SState redneF Performer 1,000 Model which was about to die showing signs of problems,,, I did the above and He has had no problems ever since. I actually mounted those drop R's off the circuit board to make sure no more issues arose from heat.

Meanwhile If saving the planet is high on your agenda then go plant a tree or better still stop buying cheap RoHS stuff made to last only 5 years.
Have fun ,, Phil.

Seiche · Post by **Seiche** » 19 May 2012, 12:46

^wait, are we still talking about the red knob fender deluxe 85 that's like from the 80ies or 90ies? What does this have to do with RoHS?

phatt · Post by **phatt** » 21 May 2012, 08:06

Good point?
No matter cause I think you will find they have been using very cheap solder long before RoHS standard came out.
My guess is it just legitimized the cheap stuff they had been using for a long time anyway.

In simple terms keep heat away from ANY wave soldered or similar pcb's if you want it to last.
Whether or not these are pre or post RoHS ,,, the issue is much the same.

Care to note how many PCB mounted Valve sockets are cracked these days

Thank god where i live I can still buy Solder that contains LEAD.

Phil.

DrNomis · Post by **DrNomis** » 21 May 2012, 08:32

See, this is the reason why point-to-point construction is sometimes better for some amps....

soniccustard · Post by **soniccustard** » 21 May 2012, 11:01

You can buy leaded solder in the UK, but just not anything built with leaded solder, it's weird.

I've taken the bits out but not put them back in yet, didn't have time. The bit that's confusing me is that I continuity tested them all before taking them out and everything works, maybe it's the transformer that's dead. Anyone know how to check the transformer?

phatt · Post by **phatt** » 21 May 2012, 11:19

A continuity test of the part is dead easy,,, Arrh but is the circuit continuity tested ???
In your case like so many others,,, the connections are likely cracked and giving intermittent connections the most annoying type of fault.

90% of all electrical problems are to be found in connections,,, in this case it sounds like the solder points letting go due to overheating.
Phil.

DrNomis · Post by **DrNomis** » 21 May 2012, 11:35

soniccustard wrote:You can buy leaded solder in the UK, but just not anything built with leaded solder, it's weird.

I've taken the bits out but not put them back in yet, didn't have time. The bit that's confusing me is that I continuity tested them all before taking them out and everything works, maybe it's the transformer that's dead. Anyone know how to check the transformer?

You can use a digital multimeter set to ohms to check if the primary and secondary windings show continuity, the high-current secondary windings should read a few ohms, and the low-current secondaries should read about a few tens of ohms, the primary winding should read at least about 100 Ohms or so, set your multimeter to the highest ohms range and check to see that there's no continuity between the primary and secondary windings, it should read open-circuit, or OL, if the secondary windings are separate, there should be no continuity between them, finally, check to see if there's any continuity between any of the windings and the transformer core laminations, they should all read open-circuit, if the transformer passes all those tests, then it should be okay, any open-circuits, or short-circuits where you don't want them will indicate a bad transformer....hope that helps....

Make sure you've got a schematic of the amp when you do the tests on the transformer....

deltafred · Post by **deltafred** » 21 May 2012, 11:40

soniccustard wrote: I've taken the bits out but not put them back in yet, didn't have time. The bit that's confusing me is that I continuity tested them all before taking them out and everything works, maybe it's the transformer that's dead. Anyone know how to check the transformer?

Disclaimer - Internet debugging is very difficult.

Right let's get this straight.

1. They aren't blown because they still read what they should, 232R & 234R is no doubt well within tolerance for dropper resistors. BUT that is on their leads, did you continuity check the solder joints, pad to lead before removing them?

2. The solder joints were not looking too good but as you have now removed the resistors you will only find out if that was the fault by replacing them and trying it.

3. If after replacing them it still doesn't work then start looking for something else.

If you need it for a gig this weekend I would start by finding an alternative because it could be a long job fixing it.