Roc Pro 1000 stuck on disortion?

[mmfn520]

Hello everyone! i have a roc pro 1000 that nees some attention. i am a automotive tech but i just dont understand the schematic i have found online about test points, theres no reference numbers as to what measurements i should be getting. my problem as follows, power up amp-take a couple seconds to warm up then turns directly to yellow light and stuck in distortion cannot change to heavier either only yellow light-amp proceeds to cut in and out going from loud to quiet. i have already tried a replacement tube but that was not the fix. noticed on the board by cr56 an cr57 there is a dark spot but not damaged. checked solder joints on board and they looked ok. im outta ideas and i really am hesitant to pay somone 100 bucks an hour to look at it plus repairs if i can fix it myself. any input or diagnotic info would be greatly appriciated!

[Jazz P Bass]

Fender RocPro 1000

CR56 is the +16 Vdc anode test point.
CR57 is the -16 Vdc cathode test point.
They are zener diodes. Sans poor mans voltage regulator.
Power up the amp & check both voltages.
They should "come up" immediately at power up.
Schematic:http://www.fender.com/support/amp_sc...ematic_B12.pdf

[mmfn520]

i dont want to burn up the board so can you clarify for me how to measure them. am i testing with my meter to ground on the carrier of the board and using the positive lead to probe the board at test points or is there a common ground on the board i must use or is there a special way to measure?

[Jazz P Bass]

Fender RocPro

Look on the schematic, page #1, bottom left corner.
That is your power supply for the amplifier.
Test Point 24 (+16Vdc) & Test Point 27 (-16Vdc) are clearly marked.
Where the anode of CR56 & the cathode of CR57 meet is 0 volts. (ground)
This point may or may not be connected directly to the chassis.
Use your ohmmeter & verify. If it is, you can connect your negative DVM lead to the chassis. Positive DVM lead will be your measurement lead.

[mmfn520]

thank you and am i heading in the right direction with my diagnosis? would you suggest any other paths im still at work so i want an arsenal of tests for when i get home haha but i will def look at the voltages on those test points

[mmfn520]

ok so to update the progress, i got home and to another look at the board and it turns out the footswitch jack was desoldered. so i resoldered that connection and fired it up low and behold i was jamin. so i figured i give this thing a workout, bout 30mins in this thing cuts out still on and all that jus sounds like when you first turn it on and the amp is warming up all you hear is a low volume guitar, same on the clean channel. wait a couple seconds or so and itll come back up. it seems im rid of one problem but stuck with another. i did not check those test spots on the board yet, i was unsure if the measurements would be accurate since i dont quiet have enough slack to plug in the speaker. anyone have any advise on how to fix my new problem of cutting out? im gonna get some jumpers from work so i can connect the speaker with the shelving out and do my electrical tests. any advise would be greatly appriciated.

[52 Bill]

First, I'd suggest trying a spare cable in the FX loop to see if that restores the signal.

As for testing the power supply voltages, you do not need to have the speaker hooked up to the amp to check these.

Just work carefully so as to not do any damage to yourself or the amp.

[mmfn520]

ok so i have tried looping the effects loop and it does not restore signal neither does plugging the guitar straight into the the return jack of amp. i have pulled the shelve out and checked my voltages i have -16v and +16 volts at the two test points 24 and 27. what else should i look for or look at? this thing has me jammed up!

[Jazz P Bass]

Effects Out Test

So now the channel switching is o/k?
If you sent your guitar signal into FX Return & you still have low volume, then something is wrong from that point on to the speaker.
First you must verify that there is NO Vdc on the output terminals. (where the speaker plugs into the amp)
If no Vdc on output:
Can you test the speaker on another amp.
Or test another speaker on your amp.
The output section of the amp is located on the schematic, right below -ON BREAKAWAY-From U7 on the left, all the way to the right , speaker out.

[mmfn520]

just to clarify what you mean i plugged my guitar straight into the back of the amp return jack, what about the switch inbetween them which setting should i have that on? i will check the speaker outputs for voltage. but i just wanted to make sure i hooked that in according to what you had suggested. how does the return send to the speaker? doesnt it just use it as a pass through as if you are using a different shelve unit?

[Jazz P Bass]

FX Return

The FX return jack drives the amplifier output section, bypassing the whole preamp.

[Lachang]

I have this exact same problem. circuit board is slightly burnt around cr56 and 57 and sound keeps cutting in and out making the LED go yellow. This seems to happen faster when I increase input volume, and especially if I use the distortion channels.

Has anyone found a solution to this?