Problems with a new Fender BandMaster V Series! Uggh!

[guitkrazy]

I picked up a fairly new Fender Bandmaster (V Series Model PR772) It was not working when I got it. I had to replace the 1k 5w resistor which was fried and I isolated where the short was that caused the issue- one those metal jumpers that look like paper clips (unshielded) had burned through the thin plastic on the board and caused a short.
This amp is nothing like the old Bandmasters that I am used to- it has several circuitboards and digital effects, not to mention the data ribbons that resemble a computer rather than an amp! Anyway, I reassembled the amp after correcting the short. Now I get a loud noise even with no instrument cable in, and when I put the cable in I get no signal out just the loud noise. I am having difficulty finding any information on this amp, does anyone know anything about this amp or any recommendations to what I should check next? Very frustrating! Any help is greatly appreciated!

[stokes]

Cant find a schem for that model.What is the 1k 5w resistor?I think it may be possible that you could be looking at this backwards.Depending on what the 1k is connected to it is possible that the "metal jumper" got hot from the resistor heating before it completely fried,in which case you didnt fix the problem.Tell us more about the 1k 5w resistor.

[Wilder Amplification]

Here's the schematic for the Bandmaster VM.

[booj]

Is the loud noise a hum? 60 hz or 120 hz? The 1k 5 watt supplys voltage to the screens and everything else on down the line. Make noise with no output tubes? more info needed

[guitkrazy]

The story behind this amp is that it was purchased unworking. We opened it up and the 1k 5w resister was blown, we replaced it and there was still a short. This amp is has literally 4 sections- Power Where the 1k5w resister is, An Effects Loop, The Front Panel (I need the schematics for that) and the Digital Effects section. The short now appears to lie in the Frontpanel section. Everything checks fine until going via a data ribbon to the front panel. Of course you have to remove every board to replace and unsolder! Uggh! I am just wondering if anyone knws what I should look for on the front panel section. I wonder if the original short damaged those TLo72 chips? I know they are easily damaged and have blown on Fenders in the past? Any help is greatly appreciated!

[52 Bill]

Originally Posted by guitkrazy

The Front Panel (I need the schematics for that)

This is all there in the schematic.

Originally Posted by guitkrazy

The short now appears to lie in the Frontpanel section. Everything checks fine until going via a data ribbon to the front panel.

What is shorted? The HV supply? The low voltage supplies?

The resistor you replaced appears to be R73 in the HV supply. Is this resistor still overheating? If it died, the cause would be most likely be a bad power tube.

[Wilder Amplification]

Originally Posted by guitkrazy

The story behind this amp is that it was purchased unworking. We opened it up and the 1k 5w resister was blown, we replaced it and there was still a short. This amp is has literally 4 sections- Power Where the 1k5w resister is, An Effects Loop, The Front Panel (I need the schematics for that) and the Digital Effects section. The short now appears to lie in the Frontpanel section. Everything checks fine until going via a data ribbon to the front panel. Of course you have to remove every board to replace and unsolder! Uggh! I am just wondering if anyone knws what I should look for on the front panel section. I wonder if the original short damaged those TLo72 chips? I know they are easily damaged and have blown on Fenders in the past? Any help is greatly appreciated!

I posted a link to the schematic in PDF format in the post above.

As mentioned above, X2 on the shorted power tube. Looking at the schematic, the screens are the only thing that can draw enough current through that resistor to fry it if a power tube short were to occur.

[michael peck]

im having a similar problem with my 5 yrs old mexican made fender hot rod deville 60 watt, kept having hums and crackles, when id hit top of amp it would quit, sent into marshall music and they replaced some tubes, wasnt it, i found some wires in 10 wire straps (like in a computer)that had some strands broke at board where it was soldered, i got board a little too hot when resoldering and had to put in shop, i had them replace them with single wires. and he fixed some other diodes or something.. but works good now but has an awful hum and sometimes a high pitched squeell.. cant use in recording studio, ok for giggin, but i wish i could figure it out, after 2 repairs im approaching the point where i can buy another amp cheaper than fixing this one.....not impressed with this amp

[Gtr_tech]

Jeez....whats goin' on with Marshall's service dept? I haven't heard great things about the guitar repair guy and they couldn't repair a deville? WTF.....is Gene still there?

[michael peck]

not sure , this is in MI, they sent it from traverse city to lansing MI, i paid $74 for 1st repair, then i had local guy work on it 2nd time for $150, when it broke again...bad design i think, wont take prolonged vibration.. would like to get it done right for once thats for sure

[Enzo]

I never met gene, but from what I have heard from others, he seemed to know what he was doing. On the other hand I wouldn;t be surprised if he moved on. I have some direct knowledge of what it is like to work for the guy whose daddy's name is on the building. It ain;t pretty. I know a lot of people who are so much happier not working for him.

Note Michael, Gtr tech and I are both in Michigan too.

[Gtr_tech]

I haven't been in there in ages. I never really knew Gene that well but I did know his (now late) brother Steve who worked for years as the tech at Stereo Center in Flint. Steve was a great guy/sharp tech and didn't grumble too much when he went searching in the dusty archives for service info I was looking for. When I worked in Flint I was always going to the thrift shops on my lunch hour. Used to haul all kinds of cool older audio gear outta those places. Steve was always my first stop looking for older service manuals.

[booj]

If the front end is the culprit, just take notes, make drawings, do whatever you have to to facilitate re-construction and tear into that section and replace the TL072's and also replace the J113's as well. When you get done you'll probably find the cause of the problem is something else, and fix it. Put it back together carefully and rock on.

[michael peck]

im not good at electronics, just tryin to get er done right this time, if i knew someone who could actually do it...havent had much luck in that dept, fender amp works but is just too noisey..probably a short in overheated board,data straps are a bad design, know other who had em come loose from vibration too.
used ampeg rocket at gig last nite, was a dinner party so didnt have to be super loud, didnt mic it either

[TD_Madden]

I passed on the head but picked-up the cab...it's pretty good (after replacing the Celestion speakers with Scumbacks).

Not quite like the old ones (I have a '68 set), but lighter.

[Repairguy]

I took a look at your schematics. If it was R73 in the HV power supply that burned open, then that means the "Z" supply got pulled down somehow. This really cannot be associated directly with the power tubes as R61 and/or R63 would have clearly burned open first (unless they too are now open?). If you haven't gotten this repaired yet, I would suggest looking for a short to the chassis of the wire which connects the "Z" supply to these resistors.
The ribbon cable would not withstand the current without melting first. you may be heading down the wrong path thinking it is on the opposite side of a ribbon cable.
Good Luck!

[Wilder Amplification]

Originally Posted by Repairguy

I took a look at your schematics. If it was R73 in the HV power supply that burned open, then that means the "Z" supply got pulled down somehow. This really cannot be associated directly with the power tubes as R61 and/or R63 would have clearly burned open first (unless they too are now open?). If you haven't gotten this repaired yet, I would suggest looking for a short to the chassis of the wire which connects the "Z" supply to these resistors.
The ribbon cable would not withstand the current without melting first. you may be heading down the wrong path thinking it is on the opposite side of a ribbon cable.
Good Luck!

R61 and R63 are a lower resistance value than R73. In order for the power to exceed the rating of the resistor, there would have to be enough current flowing through the resistor for the resistor to cause a voltage drop high enough to increase the power with the increased current flow. Well R73 is a 1K while R61/63 are a 470. The 470s would see close to 1/2 the voltage drop that the 1K would given the same amount of current flow through these resistors. Example, throwing random numbers for example's sake, given 441 volts @ 300mA through these resistors, the 1K would see a 300 volt drop across it while the 470 ohm would see a 141 volt drop.

The screens pull the most current from the Z supply than anything else that's hooked up to it. It's also much more common to have a screen short, which could definitely blow that resistor. Wouldn't necessarily mean that the screen resistors themselves would be blown...they could be...the OP never stated if he checked them or not. If it took out the 1K quick enough, the 1K would've acted like a fuse and protected the 470 ohm screen resistors before they had high current flowing through them long enough to blow them.

[Repairguy]

Please keep in mind that the wattage of these resistors needs to be considered. The 1K resistor (R73) in this HV circuit is a 5 Watt wirewound, where the 470 ohm screen resistors (R61 & R63) are 2 Watt metal film. If anything is going to go as a result of a shorted tube, it will be one of these 470 ohm resistors first.
I just had a Deluxe VM in the shop last night, which is basically the same as the Bandmaster VM. It had almost the identical problem as the one described in the original post. The problem seems to be that there are a series of wire jumpers that cross over HV traces with no insulation. Even though they don't appear directly shorted, they are prone arc when the HV is energized. This is the reason for these higher wattage resistors burning open in the HV supply. These jumpers need to be insulated and separated from the PC board. This should resolve the shorting issue originally described.