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g1 · 07-22-2011, 04:49 AM

There are voltages given on the schematic for all the switching scenarios, have you gone through them?
With no footswitch, the only critical part of the footswitch jack is that pin 2 and 4 must be connected as shown in the schematic, easy enough to check without opening the jack.
If it's the style of jack with the clear plastic cover, yes you can carefully pry it off then glue it back on again if you have to.

**Enzo** · 07-22-2011, 06:32 AM

If I take the cover off, I probably won't worry about putting it back. A zillion other amps have jacks without covers that work fine.

But like g-one said, it is easy enough to check without doing that. Look at the schematic. When the jack is empty the two contacts come together, completing the circuit through the jack. So get out the ohm meter. FInd R97 or CR23 or CR24, and see if there is continuity between them and CR21 or CR25 on the other side of the jack. Of course you must use the correct end of each component.

g-one is also right about those test point readings. That is why they are there.

Is that AC voltage at the jack or you just checked at its source? Plug a cord into the jack and see if that AC is on its tip.

Unlike some Fenders with four or five function switches, this one is simple, so here is a easy test. Plug that cord into the jack, and grab a diode. You can use one of the official 1N4448 that Fender uses, or a common 1N4148 or even a plain old 1N4007. Bend the diode so you can touch the tip and sleeve of the plug on the cord free end. Now touch the3 banded end of the3 diode to the sleeve, and the other end to the tip. That should change channels. If it does, the circuit works.

**sgelectric** · 07-23-2011, 03:41 AM

Thanks for the help.This is new territory for me and my solid state skills are minimal.

I checked the footswitch jack and it is okay.I tried Enzo's suggestion with the cable and the diode and the amp would not switch.The problem is in the switching circuitry.

I tried to work through the test points and the readings appear good at TP31 and TP32. After that they are not in the ballpark.Not even close.
I'm wondering about Q4. Does this seem to be warranted?As I stated, my solid state skills are minimal and I'm not even sure how to test it. I have no spare transistors.

Thanks again for the help. Steven

**Enzo** · 07-23-2011, 04:34 AM

"Not even close" doesn;t help us. WHAT did you get at TP33? And Q4? We don't know what you got, so we have no reason to suspect that part. Not yet anyway.

If the jack is OK, then just use the panel switches for now.

TP31 says you should get about 1v there all the time. If you do, fine.

So, TP32 says you should get half a volt and 10v as you switch the channels in and out. You get that, yes?

So move on to TP33, WHAT happens there? It should go from +16 (clean) to -13v (dirty). What is wrong?

The More Gain button doesn't do anything unless you are already in the dirt channel. Q4 is what turns that circuit on whenever the channel switches to Dirt. SO forget the More section for now. Get channels switching again and you probably will have that section working again in the bargain.

The relays that actually change the channels in the signal path are K1,K2. They are a little to the right from TP33. They run off the +16v supply. The current for them runs through R104, the LED, R84 and then the output of the IC at TP33. When TP33 is at +16, then there would be +16v at both ends of the relay, so it would be off - no voltage across it. That is the Clean. When TP33 goes to -13v, that makes 29v across the relay coil, minus whatever is lost to the resistors and LED. So the relay turns on and switches channels to Dirt. SO if TP33 doesn;t go up and down voltage, then channels won't switch. The relay coil current flows through the LED, lighting it as it goes.

SO look for +16v on the relay coils. Or just find R104, is ther about +16v on it? If not, the relays are both open - unlikely - or they are not receiving 16v popwer or a connection is broken. I bet the 16v is there. FInd the LED. Got the same voltage there? Now got the voltage on th other side of the LED? AT R84?

My spider sense is telling me to suspect the LED being open or a leg broken off or even just broken solder to it.

**sgelectric** · 07-23-2011, 06:03 AM

Thanks for your help, Enzo.

Here are the data from the TP checks.The amp is stuck in the Drive channel at all times with the LED in the yellow mode. All switching was done on the chassis panel.

TP31
+1.137
+1.137
+1.132

TP32
+ .513
+9.78

TP33
-7.83
-7.83
-8.59

TP34
-8.58
-8.58
-9.25

TP35
-8.33
-9.25

TP36
-7.37
-7.37
-8.04

I checked the power at R104.It reads +.84v.It is the same at the first terminal of the LED which is stuck in yellow mode.The second terminal reads -5.59v.The third terminal reads -3.13v.The voltage at R84 is -5.39
There is +16.8v at the junction of CR18 and CR19 on the other side of the relay coils.

Thanks again for your help. Steven

**Enzo** · 07-23-2011, 07:06 AM

OK now. TP31, TP32 are both dead nuts right on. And TP33 is stuck at -8v. TP33 should be moving from +16 to -13v. It ain't. Remember I said Q4 turns the MORE section on? Well enables it is more accurate - makes it so it functions, but only when already in the dirt channel. What controls Q4? TP33 does. SO if TP33 can't move, then neither can Q4 so then neither can TP34 and so on.

I at furst thought you couldn;t get into the gain channel, but now we hear that you are already in it and can't get out. Doesn't affect tracking it down, but I apologize for asking for all those relay voltages, since the relay and LED are on, then obviously they have power.

Let us talk a moment about solid state. If you can troubleshoot tubes, you can troubleshoot solid state. Let us not chew our fingernails over it. We are dealing with op amps here. They are simple triangles on the drawing because what is inside them is not so important - they act as little functional blocks. They have power connections, and they have inputs and outputs. I hate doing this because it goes against my grain, but look at it like it was tubes. A tube - 12AX7 say - has signal come into its input (grid) and leaves on its output. (plate) Got signal to the grid and none on the plate, and power is present, what do you do? You try a different tube. Got signal coming to an op amp IC, power to it, and nothing coming out, what do you do? You try a different op amp IC.

It could wind up being something odd, but at this point I wouldn;t hesitate to replace the op amp IC, U3. If i am right, then there you go, and if I am wrong, well, the things only cost 40 cents.

**sgelectric** · 07-26-2011, 03:53 AM

Enzo,
I took your advice and replaced U3.The Channel Select now switches correctly from Normal to Drive and the LED follows it by changing from "off" to yellow .So far, so good.........

Problems arise when trying to engage the More Drive function...Instead of switching into "boost" mode with the corresponding change in the LED to red,the amp goes back to Normal mode and the LED returns to "off".This is with the Channel Select and the More Drive switches depressed.In this mode the volume is controlled by the Normal volume control but there is a slight gain increase over regular Normal operation.
In an attempt to fix it, I replaced Q4....No change.....I then replaced Q3 and still no change. I know from reading your comments in the archive that the LED functions as an active part of the switching circuitry and not as just an indicator, but don't know if this is the source of my problem.

I took new readings at the TPs.

TP31
+1.34
+1.04
+1.02

TP32
+.53
+9.8

TP33
+16.3
-13.8
-15.8

TP34
-12.0
-5.09
-4.75

TP35
-.53
-10.00

TP36
-15.8
-15.7
+16.4

As always, thanks for all your help.Any further advice/suggestions greatly appreciated. Steven

**Enzo** · 07-26-2011, 05:09 AM

OK, you got channel switching back, progress. Now the MORE doesn;t work.

Just to be sure, you know MORE should only work when the lead channel is on. If you expect it to do something in clean mode, it won't.

You say by pushing MORE it leaves Lead and reverts to clean. By unpushing More does it come back to lead?

The LEDs are voltage references in the more complex switching circuits, but not here. In this one they are simple indicators powered by the relay coil current.

All your TP voltages look OK to me. Not sure why it would revert to clean. The MORE controls JFETs Q1,2, and if one of those gates shorted to ground, it could cause trouble, but there is a 100k resistor between them and TP36, so I don't think that is the issue. Grasping at straws, what if the red side of the LED were shorted to ground somehow - solder bead maybe? Possibly switching to it would momentariy draw excess current and cause the whole system to default? Seems unlikely.

SO let's isolate the problem. It is up in the LED area or not. So set the amp into the lead channel, we know that works. Leave MORE off for now. The yellow LED is lit. Q3, I hope you replaced it with 2N4403. Briefly short E and C on Q3 - the two outer legs. That should turn on the red LED. It won;t affect the sound, just control the red LED. Works?

And the flip side. Lift R86 from the circuit - unsolder one end and pull it out. That will disconnect TP36 from the LED circuit but leave it controlling Q1,2. Now with amp in lead, does pressing the MORE increase the gain? The red LED won't come on this way, but we can see if the circuit does switch on the more gain.

**sgelectric** · 07-26-2011, 07:16 AM

Enzo,
I'm aware the More Drive function only works with the lead channel so no confusion there.
When the More Drive button is "unpushed" the channel reverts to the lead channel
Q3 was replaced with a 2N4403. Q4 with a 2N4401

When Q3 was briefly shorted across E and C the red side of the LED did not come on.

With R86 lifted out of circuit, the Channel Select would not change out of the Normal channel.....However, with the Channel Select switch in the pushed (on) position,the amp stayed in the Normal channel but allowed the More Drive boost to operate when switched.As expected the LED stayed off.
Thanks,
Steven

**Enzo** · 07-26-2011, 09:07 AM

Does your pc board say 2001 or 1996?

Hmmm, I see I interpreted something wrong. The dual LED makes red and green. Red and green together makes yellow. Honest. I had been thinking one side turns on then the other. But now that I look closer, whenever the lead - more or not more - is selected, the red LED is always on. For regular lead, BOTH LED sides are lit, making yellow. When MORE is turned on, it turns the green side OFF, so the LED then appears red.

You seem to have a problem with the green. Your red light comes on for lead, but the green does not. SHorting Q3 SHOULD turn on the green side, but it doesn't. Verify that there is supply voltage coming down to the emitter of Q3. What happens at the base of Q3 as MORE is turned off and on? Diode test the green side of the LED, does it measure like an LED?

Explore CR19, R85,88, and the dual LED. SOmething there is not right.

**sgelectric** · 07-29-2011, 03:46 AM

Enzo, I checked the components you suggested and found the problem.It was the dual LED. The amp is now switching correctly.Thank you for the help and support.

Although I thought I had checked it, in fact the red side was blown.I was mistaking the green (greenish-yellow) side for the yellow that should show when the amp is in the lead channel.When the More Drive was selected,the green side correctly switched off leaving the indicator "off".I assume that the lack of any current through the LED circuit defaulted the amp to the normal channel.I found the problem when I noticed there was no voltage drop across R104 when there should have been.I installed a generic bi-color LED and the amp worked.I still need to source the proper LED.

I've learned quite a bit trouble-shooting this problem and appreciate the time and energy you expended helping to walk me through the process.The on-line mentoring that you and the other experienced techs on this forum provide is invaluable to aspiring techs such as myself. Steven

**Enzo** · 07-29-2011, 07:33 AM

Cool, I am glad it panned out.

Yes, the current to energize teh relay flows through teh LED. Open LED, no relay.

A square bicolor LED of proper electrical arrangement should be easy to find. Mouser, Digikey, Allied, and for some reason, when I want LEDs I always seem to find what I want at Jameco.

**strum_101** · 08-17-2011, 07:29 AM

Hi everyone, my first post here. I recently was experiencing the same switching problem with my FHRD. It turned out that one of the 5W 470 ohm resistors went bad. Anyways, I ended up replacing both of them and got the channel switching to work properly. Thanks to the tremendous amount of knowledge and expertise in this site. I couldnt have done it myself without threads like this one here.

Anyways, the real reason why i thought id post a reply is to see if any of you guys have tried substituting the U3 for other OP AMPS. In the process of fixing the switching problem that I had , I thought I'd replace U3 but I havent been able to find the exact OP AMP locally. Instead , iIused a Burr Brown OPA 2604 chip that I had laying around. I have used a similar chip to do a mod on an Ibanez TS9. Well, the BB worked in the HRD and i thought it sounded great. The clean channel sounds fuller and the drive channels are more boutique sounding. I compared Data sheets for both the BA4560 and OPA 2604 and they seem identical. Any of you guys have any experience with this? Maybe theres another thread about this soemwhere on this board?

BTW i installed an IC socket for U3 so i can easily swap IC's.

**Enzo** · 08-17-2011, 10:13 AM

Hi, welcome, we're glad you're here. That's the good news.

The bad news is that U3 is not in the signal path, all it does is shift DC levels to turn on and off relays and other control lements. ANY op amp will work there, and should make zero difference in the sound of the amp. Imagine changing say the power and standby switches to some other brand and expecting a sound change.

U1 is in the signal path, but only when driving something in the FX loop. Otherwise it is bypassed. U2 is the reverb circuit. It also is in teh signal path, I amnot sure how much different sounding the reverb would be with other chips.

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