Trace Elliot Commando Bass

Hi all...

I have a Trace Elliot Commando on the bench. My friend who owns it says it "died" a few years ago and went dead silent. It blows the fuses right at start up.

I have tested it with a "lamp-limiter" and the voltages are completely wrong or absent.

According to the schematic the amp is fed with voltages from two different rectifiers.... one for the preamp and one for the power section. If I unplug the power section all voltages in the preamp section is just fine so I have my thoughts it is in the power section.

I am not very familiar with all these transistors and I hope that some of you might help me where to look for the problem.

I must mention that I have changed all the electrolyte capacitors (not so many) but the problem still exists.

Grateful for all inputs

Best regards

/John

You should check all TIP transistors (desolder them first) and surrounding resistors using a DMM. Most probably one of output transistors is faulty.

TIP35 and 36 shorted,

want to replace or upgrade for bullet proof?

orig data sheet

https://www.onsemi.com/pub/collateral/tip35a-d.pdf

write down the big 3,  V, I,  hfe

V  100  I  5  hfe  15 to 75

now cross ref replacement,

looky here, 1 extra amp,  same volts and gain,    order now,

http://www.farnell.com/datasheets/40034.pdf

want more beef? check tip50 etc. cant vouch, just guessing tip 50 is beef.

buy drivers too as they usually go down with the ship. or get partial damage to fail later.

moamps said:

You should check all TIP transistors (desolder them first) and surrounding resistors using a DMM. Most probably one of output transistors is faulty.

Click to expand...

Thank you sir

In fact I have already ordered these Output transistors.

Hopefully it will work.

Just a thought... could it be the rectifying bridge for the power section?


Best regards

/John

CJ said:

TIP35 and 36 shorted,

want to replace or upgrade for bullet proof?

orig data sheet

https://www.onsemi.com/pub/collateral/tip35a-d.pdf

write down the big 3,  V, I,  hfe

V  100  I  5  hfe  15 to 75

now cross ref replacement,

looky here, 1 extra amp,  same volts and gain,    order now,

http://www.farnell.com/datasheets/40034.pdf

want more beef? check tip50 etc. cant vouch, just guessing tip 50 is beef.

buy drivers too as they usually go down with the ship. or get partial damage to fail later.

Click to expand...

Thank you sir

I will have a thorough look at it and buy those drivers as well

Best regards

/John

johnheath said:

Just a thought... could it be the rectifying bridge for the power section?

Click to expand...

Good question. Maybe. You can check it easily with "diode" position on your DMM.

moamps said:

Good question. Maybe. You can check it easily with "diode" position on your DMM.

Click to expand...

Thank you sir

Just did that and there is a voltage drop in both directions on all four diodes in the bridge... I must be said that I have not desoldered the bridge before measuring though... is it necessary?

Best regards

/John

Unsoldered the bridge and it seems to be just fine


Best regards

/John

Ive repaired a few Trace's in my day , almost always mosfet troubles , sometimes they seem to work until you gig them, then they make farting noises after a while , and power drops down to almost nothing . The fets are expencive now as I believe they were'nt made by many manufacturers . Anytime Ive swapped out the output transistors they came back to life good as new . I never actually had one that blew a fuse though ,just sounded bad at volume I scrapped a couple of the smaller ones along the way too . Sometimes they have a nice Jensen mic transformer inside , wired step down  as the di outout. There a good sounding amp when they work , I recall the screen printed legend on the pcb saying 'The Bipolar bear' on one version I fixed .Its a shame the marque doesnt exist any more , they were really popular for a while .I have a series 6 GP12 , with the nice 3 way traffic light  O/L indicators ,12 band graphic and the usual pre shape ,foot switchable , the power amp is faulty in it but it still works great via the Jensen TX as rackmount bass pre DI, the power amp can remain muted  .Its nice to have the Trace sound in the rack and  many players are instantly comfortable with getting a sound out of them . I think the biggest one I handled over the years was one with the UV lit front panel and 800 watts . The typical 200 watt combo with 15 inch cab was always a bit underpowered even for smaller rock gigs .

Thank you sir...

Yes, after replacing the FETS and recapping it works again... it proved that I had replace them all.

Thank for the tip

Best regards

/John