I have a Crate SPA400 power amp (chip) . It was banged up in transport and had a leg busted loose on the volume pot. I did not catch it until I had powered up the amp and tried to use it. I went ahead and fixed the issue with the pot, but no output. It has a input signal (led flashes). Normally this amp starts in protect mode then clicks out of protect a couple of seconds after start up. Now it stays in protect mode. I was going to look at the power rail first, but thought I would throw it out there for suggestions of where to look first?
Cliff you seem very knowledgeable in the semiconductor field, I was hoping you might have some insight or suggestions.
As long as the power amp had a load when powered on I would suspect its OT is good.
Keep in mind some fuses are also in the form of diodes. Look around the protection switching its most likely a one time use fuse. That will need to be replaced.
selloutrr wrote:Should have several internal fuses.
As long as the power amp had a load when powered on I would suspect its OT is good.
Keep in mind some fuses are also in the form of diodes. Look around the protection switching its most likely a one time use fuse. That will need to be replaced.
There were four internal fuses that I saw while I was repairing the damaged pot. They all passed a continuity test. I will have to go back in and look for any other fuses or protection diodes in the protection circuit. Since the pot was an obvious problem I was hoping that would repair the issue, I just checked the fuses I saw out of habit, I really didn't look for any more.
First thing to do is to get a schematic (if you can, I can't find one!) and check voltages. Since it's solid state I doubt it's much over 40V or 50V at the highest point but you should be able to find some common op amps and check the +/- power on them (assuming they are running bipolar supplies). If the supply is lower than it should be you probably have a bad power amp IC that is causing the supply to sag.
Even if you can't find a schematic you can usually google the part number for the power amp IC and the other active discretes and figure out what they are rated at voltage-wise.
If the power supply voltages all check out then it's time to whip out the oscilloscope and/or audio probe and start testing everything stage by stage until you find where the signal stops. A signal generator or some sound source is handy so you don't have to strum a guitar with your feet while you try to trace out signals. If you can isolate the trouble then you know what area to at least start examining further.
It's funny how quickly one can be humbled with electronics. I just built up a DOD250/TS808 in a single pedal and while the 250 side fired up no problem, I can't get a lick of sound out of the Tubescreamer side. I scratched my head and fixed a few obvious problems and all of the voltages check out...but no sound.. I just gutted it so I can rebuild just the 808 section and see where the problem is but dang, that pedal was all ready to go if that damned 808 would have worked right!
Thanks Cliff, I think finding a schematic might be the hardest part. Crate was bought out by another company. I found the schematic at that sight a while ago, but now I can't remember the name of the company that took over Crate. I want to say......Tapco????
marcoloco961 wrote:Thanks Cliff, I think finding a schematic might be the hardest part. Crate was bought out by another company. I found the schematic at that sight a while ago, but now I can't remember the name of the company that took over Crate. I want to say......Tapco????
will do some more looking.
It's Loud Technology.
Tapco is part of EV/Telex.
I had problems getting a correct schemo for a Crate guitar amp that had been revised before they sold out.
They had schematics for the model in question that did not match what I was seeing.
I was able to talk with a tech at the new company (Loud) but he said that's all they had received from the old company when they took over.
marcoloco961 wrote:Thanks Cliff, I think finding a schematic might be the hardest part. Crate was bought out by another company. I found the schematic at that sight a while ago, but now I can't remember the name of the company that took over Crate. I want to say......Tapco????
will do some more looking.
It's Loud Technology.
Tapco is part of EV/Telex.
I had problems getting a correct schemo for a Crate guitar amp that had been revised before they sold out.
They had schematics for the model in question that did not match what I was seeing.
I was able to talk with a tech at the new company (Loud) but he said that's all they had received from the old company when they took over.
rd
Loud, that's it, thank you. I will feel better if I can look at a schematic first.
Turned out that the traces to the pot were damaged also. looked like a good connection but it was intermittent. Had to replace the wiper trace and one of the other traces with a wire.
The biggest problem was a loose connection on the three prong connector to the board from the power transformer. One side was loosing connection and causing that rail to drop out and keep the protect engaged. Had to figure out how to remove the wire end from the 3 prong connector and tension up the connector. Weird system. Once it had good contact the protect kicked off and it works. Thanks for your help and suggestions everyone.
. It was banged up in transport and had a leg busted loose on the volume pot. I did not catch it until I had powered up the amp and tried to use it. I went ahead and fixed the issue with the pot, but no output. It has a input signal (led flashes). Normally this amp starts in protect mode then clicks out of protect a couple of seconds after start up. Now it stays in protect mode. I was going to look at the power rail first, but thought I would throw it out there for suggestions of where to look first?
