Traynor monoblock 2

[AlNewman]

Hi,

So somehow I ended up with a solid state Traynor that a widow wants to get working to sell.  This was through another guy who tried selling it already, but everytime he tried to fire it up it kept blowing the circuit breaker... go figure. 

It was in storage for years, and must have been stored in a fishing boat bilge, because most of the board and screws were covered in a good layer of corrosion.  Fair enough, I cleaned up the board and hooked it up to my lightbulb, and was able to trace some problems.  It was all very distorted and weak signal, and when turning up the master volume, the amp would short intermittently.  Turns out the IC before the master volume had failed, as well as the thermal breaker wouldn't hold anymore.

So I ordered these parts as well as all the caps, replaced everything, and I thought I had it beat.  I fired it up on the current limiter, and it was sounding ok, but had an underlying distortion while I was playing it.  I played for about 5 minutes, and I ended up digging in and playing a bit harder, at fairly low volume because I don't have a cabinet that will handle 325 watts, and ended up frying one of the power transistors on the negative rail.  Shit.

So I unhooked all the transistors from the negative side and was able to find out the pre amp seems to be working fine now, it is clear, it isn't really a sound I would enjoy, but it seems like it's working as intended at least.  I was able to find a failed diode, D5, which I replaced, as well as the 22 ohm resistor R29 was reading 30 Ohms so I put a 110 Ohm 1 watt metal film in parallel, now it is reading just slightly over 23 ohms.  It seems like the rest of the transistors and diodes test ok in circuit, and the resistances all seem to line up, though my meter doesn't read the .27 ohm resistors very well so hard to tell.  One anomoly with the voltages, is that at the junction of D5 and Q8, it reads -5 volts, which seems puzzling to me and out of place.  Is this normal?  I pulled Q8 and tested it, and it tested fine.

I can't find data sheets for any of the power transistors for this amp, but in the revised version all of the npn power transistors were replaced with 2n3773, so I plan on ordering 5 of those.  Even though the revised schematic kept the SJ 5480, I found that the complimentary transistor would be the 2n6609, so I will order one just in case, as well as all new mica shims and some heat sink paste. 

The 2n3773 transistors my supplier carries are rated at 15 Hfe, but they have 2 different PNP 2n6609, one is 60Hfe, and one is 5Hfe.  I'm wondering which one would be the better part to order in case I need it?

Also, is there anything else I should be looking for before putting the transistors in?  I'm really not familiar with biasing transistors at all, but I'm trying to learn as I go, hopefully without blowing brand new parts, or sending an amp out which is destined to fail again.  I'm hoping that since they used these new transistors as replacements, and it seems to be the only part of the circuit that was changed, they will just be a drop in replacement. 

How should I be checking bias once I do replace the transistors?

Thanks

Schematic:

https://el34world.com/charts/Schematics/files/Traynor/Traynor_monoblock_ii.pdf

[shooter]

have fun 


the .27ohm and 100ohm "set bias", I believe.


I typically meter volts across the .27ohms for each side along with both rail volts, hoping to catch one or the other outta whack.

[AlNewman]

have fun 


the .27ohm and 100ohm "set bias", I believe.


I typically meter volts across the .27ohms for each side along with both rail volts, hoping to catch one or the other outta whack.

Yeah, I'm not sure luck will do it, but can't hurt I guess.

I'd like to send it back to be honest, it wasn't working when I got it, and it ain't working now.  I've already got time and money invested now though, and I did have it working, that's the kicker.  The negative voltages seem good, I can't seem to find any bad or drifted parts.  Would the one failed diode be enough to fry the transistor?

[shooter]

Don't get to stuck in the mud, SS troubleshooting was developed during the dark-ages 
unless you've worked on many SS systems and love a masochistic experience, send it back


i made a living with SS systems, i'm less than 50/50 on complex SS audio equipment, the last fail was a Pioneer quadraphonic, after 6mths i gave it back and decided the aggravation wasn't worth the thrill off defeat 

[sluckey]

Be careful. In the blink of an eye you can destroy ALL of those output transistors.

[AlNewman]

Don't get to stuck in the mud, SS troubleshooting was developed during the dark-ages 
unless you've worked on many SS systems and love a masochistic experience, send it back


i made a living with SS systems, i'm less than 50/50 on complex SS audio equipment, the last fail was a Pioneer quadraphonic, after 6mths i gave it back and decided the aggravation wasn't worth the thrill off defeat 

This actually made me feel better.  Thanks.

[AlNewman]

Be careful. In the blink of an eye you can destroy ALL of those output transistors.

This I know....  Tubes are so much easier, they talk back.  "You want to feed me bogus voltages, I'll wipe out every component in your amp!  How do you like that?"