Fender reissue TR

[Stevem]

Anyone have a schematic for one of these?

This ones got dates on the board that have a range of up to 2009, but this main board has a added fuse on it near the bias filter section, and boy does this amp have a new to me strange problem that I may be posting back about.

Thanks in advance!

[solderhead]

I've got the complete Fender service manual for the 65 Twin Reverb Reissue. I'll send it your way.

edit: YGPM.

[Stevem]

Thanks for putting the time in to find that , but that’s what I found and have been working with even though it’s not 100% correct.
What’s not the same is this second fuse that you see in my photo.

[solderhead]

I don't understand your problem because you haven't actually told us what the problem is. That said, I see a burned bias circuit on the PSU end of what looks like a generic Fender main PCB.

Let's start at the beginning. When asking for help, it's helpful to offer 3 pieces of information in your first post:

1. Give the name, model, revision number of the UUT.
2. Post a copy of the schematic.
3. Fully explain your problem.

So far you haven't provided any of that information, which means that anyone who wants to help you needs to be clairvoyant.

Without knowing #1, #2 or #3 I tried sending a schematic because you didn't have one. It would be really helpful if you could tell us the revision number of your amp and the nature of your problem. It would also be helpful to know what level of experience you have servicing amps, so that responses are written in an understandable way.

[sluckey]

I don't understand your problem.

The problem is that he can't find a schematic that accurately represents the amp he's working on.

[solderhead]

Sorry -- it looks like I was editing my post while you posted yours.

The schematic 'not accurately representing' the amp he is working on is not of significance. We're only talking about the addition of a fuse to the PCB and there's no point of getting hung up on that.

None of the Engineering Change Orders in the Fender reissue amps were ever significant. The reissue amps were all just reissues of the original Fender circuit. The ECO amounted to things like minor part value changes that would not effect serviceability of the amp.

Early reissue amps didn't fuse the heater supply circuit but the later amps did. The only difference between them is the absence of, or the presence of, fuse XF2 (heater supply) on the circuit board. The Service Manual that I sent to him clearly documented fuse part # XF2 in the Bill of Materials. His photo shows the existence of XF2 on the PCB. If the layout diagram that he has omits the fuse, then just pretend that it's there, right where it is on the PCB and move along. The heater circuit has not changed.

It doesn't make sense to get hung up on whether or not the amp is sending the 6.3V heater line into a fuse. Just test the fuse for continuity and move along to the 800lb gorilla in the photo -- the burned bias circuit.

@stevem -- could you tell us the board revision numbers on your amp, and more importantly, how the amp is misbehaving?

[Stevem]

Hi folks .
I resolved the low B+ issue that it had by accident it seems.
I was probing around to find out what that fuse was for and I guess there was a poor connection on one of the spade connectors.

Now I need to find out why the normal channel has less then 1/2 the gain of the vibrato channel.

It’s not due to tubes or any components on the main board so it’s on to the removing the front control board.

I will keep you posted.

[B Ingram]

Now I need to find out why the normal channel has less then 1/2 the gain of the vibrato channel.

Are you comparing AC Voltages from Normal channel to Vibrato channel?
Or are you comparing AC Voltages from Normal channel to those indicated in the Service Manual?


The Reverb Mix stage adds a gain of at least 3-4x, even after signal reduction due to the mixing resistors (3.3MΩ, 390kΩ, 220kΩ) used to mix the reverb & dry signals in the Vibrato channel.

[solderhead]

> Now I need to find out why the normal channel has less then 1/2 the gain of the vibrato channel.

I'm assuming that by "gain" you mean the amount of measured voltage gain that you measure when injecting a 1 kHz test signal, right? I mean, Twin Reverbs aren't considered to be "gainy" amps in the way that most people use the term "gain" today.

Before you attempt to compare the channel voltages check to be sure that you've followed the test conditions noted on the schematic -- line voltage adjusted to 120VAC with a variac; bright, switches, reverb and vibrato off; all normal channel controls at full CCW; all vibrato channel controls at 50%. The voltages that are measured in each channel aren't expected to be identical. See the schematic.

As B Ingram mentioned, it's important to understand that the vibrato channel will produce varying signal levels. that can be difficult to interpret unless you follow the official test procedures. Otherwise you'll end up with an apples to oranges comparison.

Before disassembling anything I always try to get a bird's eye view of the amp by measuring every stage of the PSU rails, then checking all pin voltages. Sometimes that allows quick recognition of problems like poor connectors and prevents wild goose chases.

[Stevem]

Thanks for all the replys folks.

No I have not traced thru it looking at signal levels, but I have been fixing Fender amps for 55 years and this low signal level I am having I do not think is related to the mixer circuit, because the Eq section is not fuctiong right either.
But until I get in there this evening I will not rule out the mixer stage.

[captaincoconut]

None of the Engineering Change Orders in the Fender reissue amps were ever significant.

Ever had a EU version of any Fender BF amp with tremolo on your bench? They have these two additional pcbs installed just to replace the optocoupler used in the tremolo circuit. Yes for real, two additional pcbs to replace a SINGLE part! They started to use these in EVERY tremolo amp from around 2007 or even a little earlier. That's quite a significant change innit?

[Stevem]

That's flat out insane!
What could be the resoning behind added so much cost to the amp?

[solderhead]

None of the Engineering Change Orders in the Fender reissue amps were ever significant.

Ever had a EU version of any Fender BF amp with tremolo on your bench? They have these two additional pcbs installed just to replace the optocoupler used in the tremolo circuit. Yes for real, two additional pcbs to replace a SINGLE part! They started to use these in EVERY tremolo amp from around 2007 or even a little earlier. That's quite a significant change innit?

D'Oh! <smacks forehead>

I wasn't thinking of that as the reissue of a vintage circuit because ... well... that clusterfuck excuse for a tremolo isn't really a vintage circuit.

To be fair, that EU RoHS tremolo fiasco was actually a Bureaucratic Change Order, not an Engineering Change Order. No engineer ever thought that was a good way to design a tremolo circuit. That circuit was mandated by EU environmental leglslation, not an engineer's design to improve the amp.

Correct me if I'm wrong on this part:
Steve, the backstory is that in about 2007 the EU passed RoHS legislation that effectively banned the Fender tremolo roach because the RoHS directive determined that all CdS photocells were environmentally hazardous due to their cadmium content. The EU banned all CdS photocells (including the tremolo roach) and Fender had to design that 2 PCB monstrosity to replace a single LDR/lamp combination. I'll leave it up to you to determine whether there was more negative environmental impact caused by the photocell or the bureaucratic mandate that required the manufacturing of those two PCBs to replace one LDR.

If you're interested in this, a google search for "RoHS Fender tremolo" should get you some hits. The Americas and European users at Ampage/MEF had a very lengthy discussion of this back in the day but that information seems to have scrolled away now.

See what happens when a bureaucracy runs out of control? Legislation facilitates bureaucratic edict and as the size of the government bureaucracy continuously enlarges, people are forced to navigate a Byzantine maze that leads to ridiculous compliance solutions. These are the kinds of results that come from excessive regulation. <ducks for cover>

[nuke]

Yeah, EU regulations banned the use of cadmium, even the tiny amount of it used in a cadmium sulfide light-dependent resistor.

There was an exemption allowed for a while for musical instruments, but that's gone away.

The EU regulations are also the source of a lot of extra fuses and other doo-dads, finger guards and all kinds of stuff.

So, no vactrols or optical tremolo systems allowed in EU and if the amps are intended for world markets, they have to be built to pass all the local regulations.

They're still legal in the US, despite ROHS practices.

Hence Fender's '64 Deluxe Reverb hand-wired has a bias modulating tremolo.

Generally, in mass production, the idea is to have as few variants as possible.

[Stevem]

Unelected Bureaucrats going off the rails with power like has been going on here in the US for too long even though it has not been to the extreme like with what’s been posted here.