Fender M-80

[Enzo]

A+.

The M and B pots down become zero ohms to ground - grounding the bottom of the T pot. Turn T all the way down and the T wiper is now connected to ground through those other two pots. AS soon as you turn up the T, then it is no longer grounded and signal starts to pass. On the other hand, leave T at its zero, but raise one of the other ones. Now the bottom of the T pot is no longer at ground, so neither is its wiper even though at zero. So sound passes.

SOunds like you probably have it now. I hope you learned somethng about the process of troubleshooting, as opposed to just finding out what to change to make this amp work.

[pchilson]

Well, its a small step down a very long road. Lets put it this way, I know more now than I did going in...Thanks

[pchilson]

Today my parts came in from Allied.
I installed 2 new TIP142
I installed 2 new TIP147
I installed 4 new BYV26Ds
There are no shorts across collector to emitter.
I hooked up CP5 rail alone - fuse blows
I hooked up CP7 rail alone - fuse blows
I hooked a jumper from Q3 base to Q5 base, both rails hooked up - fuse blows.

Why now is it blowing fuses on both rails when in post # 71 Q3 and Q5 were missing from the circuit and the amp was operating. Now its not.
I guess I'm just not going to get this amp working again.

[Enzo]

REcheck the main rectifier diodes for shorted, and verify none of the output transistor tabs are grounding to the heat sink.. And of course make sure the 142s and 147s are in the right holes. Look on the underside of the board, any untrimmed leads touching anything?

Are we using 4A fuses - you are on 120v mains, right?

[pchilson]

Hoooray! It lives...!!!

REcheck the main rectifier diodes for shorted, and verify none of the output transistor tabs are grounding to the heat sink.. And of course make sure the 142s and 147s are in the right holes. Look on the underside of the board, any untrimmed leads touching anything?

Are we using 4A fuses - you are on 120v mains, right?

Enzo, You've done it!!! You've cracked another case wide open...

First thing I checked, after I saw your post, was the xstr tabs to ground and sure enough both of the TIP147s were shorted to ground. That mica pad they use is ok but that plastic collar on the screw is kinda hokey. Anyway I got them isolated from the screws and all is working fine now. Man, I was getting depressed about this thing and you walk in and save the day...hehe. Man what a relief to get this working again. I can only thank you again as I never would have gotten it working again without your sticking with me on it.

Thanks again.

[Enzo]

Glad it works.

Those plastic T-washers have the thin little collar that fits down the hole in the transistor to keep the screw from touching the sides. YOu do have to watch out for it.

[Lee_ranaldo]

i'm fixing an rocpro 700 fender combo amp with the same output stage desing

high performance single op-amp with a pair of darlington transistors

beware!

TIP14X darlingtons are very WEAK and sensible in terms of heat.. i was measuring voltages with the amp board on chassis but i0ve removed some screws that attachs a big block of aluminum that transfers heat from anothar aluminum bar attached to a pair of TIP142 & TIP147 transistors

the TIP147 transistors overheated like an oven and shorted out after a few test. The fuse is blown obviously.

I'll replace this and replace the thermal grease on this amp.

Please avoid running this amp without a fan or something or these tip will die sooner than you expect

is the classical problem with tip transistors. i usually fix some car alarms that uses those transistors to drive the horn and they also die because of this heat issue.

[Enzo]

That is why they are bolted to the heat sink. When those transistors are not on their heat sink, they willl quickly overheat. Also the thermal tracking transistor will no longer have the heatsink to thermally track, so it cannot compensate as it is designed to do. That hastens the blow up. These transistors are actually very reliable. You cannot operate amplifiers removed from their heat sinks for more than a couple seconds.

[Lee_ranaldo]

I'm fixing this Rocpro 700 with the same problem i guess.

The main problem was one of the "tips" was very hot without using the amp at high volumes. Then some diodes CR21 (1N414X) and CN22 (1N5222 3.9 Zener diode) were shorted. I replaced all the suspicious components and one of the tips (TIP147) that was shorted..

i turn on the amp, same problem, fuse blows, new TIP 147 shorted betwen Base and colector.

one of the caps connected to -VCC was bad with no signs of electrolite coming of. This cap is connected to the emiter on the TIP147. Also the TIP142 had a shorted base/colector symptom .C48 22uf /16 Electrolitic Cap in the ROC PRO 700 Schematic

The pin 6 of the MC1436 Puts about 20 Vrms AC without the TIP transistors soldered. (OD channel Volume Maxed) and all the controls as specified in the service schematic


Can i use a CA3140 as a replacement? both are high voltage single op-amps

the CA3140 max vcc is about +/- 35 Vdc Max and some versions of the MC1436 are +/- 28 Vdc Max.

[Enzo]

I thought your 1436 was working - it puts out 20v of signal doesn't it?

I generally don;t mess around, when a TIP output transistor blows, I replace them all.

[Lee_ranaldo]

Yes enzo you were right again.

MC1436 it's fine

i replaced both TIP's and works like a charm.

i did a complete cap job on this and it's warmer than ever. i replaced the coupling caps in some stages with some capacitors that i had from a boss mod that i did, and it warmed up the tone a little bit.

Those caps are to "cheap" sounding but in this cases it's rolls off some bass and unwanted "high" frecuencies, making it much more warmer than before

thanks enzo! again!.

[jimdangle]

loud hum and not much else from performer 1000 hot mc1346?

Hi,
could someone please help?
I have a fender performer 1000, a soldering iron 30w, and a multimeter. I took my amp in because of crackling issues. Then it started blowing fuses. Then the tech got it to stop blowing fuses, it played some music through it for a minute or two, then no sound would come out. No fuse blowing though, but a loud hum remains audible whenever the amp is on. The tech pointed out that U7 in the schematic IC OP AMP MC1436 was getting very hot. We decided to buy a replacement mc1436 (actually I went with something that I think is a suitable substitue OPA445AP High Voltage FET-Input Op Amp DIP OPA445 - eBay (item 260271918642 end time Nov-29-09 18:00:03 PST) - is an opa445ap going to work? The only thing I am unsure of is if the ap on the end of opa445ap makes it unsuitable?)

also, the tech showed me when I first brought the amp head in that q11 and q13 were broken (burnt out?) so we put in a tip142 in q11 and a tip147 in q13...have a question about the tip142 and tip147 output resistors you place in the amp.** The quote form a forum below seems to indicate a new set of four should be put in (two new 142's and two new 147's):

"In sincerely doubt it is the caps, and while rectifier diodes could be shorted, they are way down my list. The most likely thing bad here is the output power transistors. The two tab types on the heat sink - TIP142 and TIP147. Legs 2 and 3 are probably shorted together. If one is bad, replace them both.

Make sure neither .47 ohm ballast resistor is open - R65,66. ANd see the eight diodes to the left of the output transistors on the schemo? MAke sure none is open or short. In the case of the zeners, if they act like a diode, they are OK. While you ar at it, might as well verify that R61-64 there are close to their values."

from:* http://music-electronics-forum.com/t1922/

Correct me if I'm wrong, but I believe you just put a tip142 in the q11 slot and a tip147 in the q13 spot...it seems kind of wasteful to replace all four of these output resistors if a multimeter could discern whether q12 and q14 are shorted or broken...

you indicated the replacements I bought were not the to218 form...does that mean I cannot use the replacements I got?* I think they are darlingtons, like the fenders...they seemed to match up the hole for the screw and the 3 tracers, even if the black body was a bit larger...

Now, I am wondering what other parts should I buy in attempting to fix this and what and how should I use my multimeter to test things...i am pretty much a total novice so super simple yet detailed intrucstions would help. It is expensive to keep going back to the tech....

browsing forums I kind of decided to buy the following replacements parts (though I did not test them to make sure they were broken....probably not that smart, huh? How do I do that though?)
4 of item number 028776 * DIODE BIAS BYV26D LEAD FORMEDCR25-28
CONTENTS:
Parts marked with an asterick (*) indicate the required use of that specific part. This is necessary for RELIABILITY
and SAFETY requirements. DO NOT USE A SUBSTITUTE! Says the fender manual

also, I wonder if not using the right kind of mica pads under the tip142 and tip 147 caused the problems or if the plastic screw coat isn't preventing the transistors from grounding, how do I tell? Does the termal switch need mica pads or screw insultators? It currently just has two screws and nothing else. Lastly, do the screw throughout the boards body serve some function such that they need to all be screwed in when testing?

One other thing, the tech was poking the multimeter around the out to speaker jack on the head, the one that says “use this for a single 4 ohm load” and a large spark or flash of electricity appeared for a split second, the size of a golf ball, bluish....what does that mean? I can take pictures if anybody wants them and I actually took a lot of photos and posted research earlier in this ordeal at fender performer 1000 head board - a set on Flickr

that was before this last trip to the tech (after I ordered replacement tip142 and tip147 output transistors) were the tech got the amp to power on without blowing fuses, played for a little while, then wouldn't play sounds but would hum loudly and the mc1436 was very hot to the touch...

Thanks,

[jimdangle]

also, my tech sent me this:

This is what I think is going on. 1. Perhaps mc1436,C was also damaged by whatever mishap caused TIP 147, TIP 142 to short. This damage was not evident until a few seconds of seemingly proper operation of the output stage. 2. Something else? caused MC1436, C to overload/overheat? I was wondering if the spray residue that is all over that board is at all conductive and that would have caused too much current to damage the MC1436,C? Anyway, the IC seems to be damaged and the only way to be sure is to replace it. All of that other stuff you mentioned is OK, and is not an issue. After the MC1436 is replaced, there is/are still a problem(s) from the input jack.
Let me know if you are able to locate a replacement IC. I don't know where to buy one. I know of a similar IC made by Fairchild, that you can buy for about $10. plus shipping.


i shoudl point out that i bought the 2 pack from radio shack of deoxit yellow and red versions and applied it liberally to the board...

[Lee_ranaldo]

i'm not an expert but my guessing is.

- Lost bias. the pair of power transistors needs a bias voltage so they operate withing range. if this voltage is lost, the power transistors will disipate the maximum power possible and they will go short in a few minutes.