Amp repair: Traynor Bloc 40B

[MtManiac]

I’ve an old Bloc 40B that my dad bought new for me way back in 1986, and I used it pretty much exclusively until about 2007-2008, when it started sounding overdriven anytime I played through it. I’d like to repair it, but it isn’t worth spending a lot of money on. How would I best troubleshoot the issue and repair it? If it’s just replacing a pot or something, that’s no big deal.

 

[agedhorse]

Until you can identify the actual problem, you won't know what may (or may not) need to be replaced.

How much electronics do you understand, and what tools do you have?

 

[GrapeBass]

I’ve an old Bloc 40B that my dad bought new for me way back in 1986, and I used it pretty much exclusively until about 2007-2008, when it started sounding overdriven anytime I played through it. I’d like to repair it, but it isn’t worth spending a lot of money on. How would I best troubleshoot the issue and repair it? If it’s just replacing a pot or something, that’s no big deal.

Bring it in to Long and McQuade, ask for an estimate.
[Invalid or Expired Link Removed]

 

[MtManiac]

Until you can identify the actual problem, you won't know what may (or may not) need to be replaced.

How much electronics do you understand, and what tools do you have?

Honestly, not a lot of understanding or tools. I do have a multimeter, but I have a guitar player friend who is a Major in the Forces who is an electronics engineer, and a drummer who is a retired avionics technician, so I figured I could let them have a look at it if I could determine what the problem was - I just didn't want to hand them a "bag of hammers".

I took it into L&M a few years ago, and their assessment was just simply that it wouldn't be worth repairing, since it is so old and has no resale value. I'm not interested in resale value, but if it cost $100 to repair, I'd repair it. With labour, they figured it would be close to $200 to repair, so I'm looking to do it with free labour where I can.

 

[agedhorse]

In general, I can't see anything on that amp that would cost more that $100 for a real tech to fix. $200 is the crazy day retail price of such a repair imo.

Talk to your buddies, they should have the tools and education to sort it out.

 

[beans-on-toast]

This is a 40W transistorized combo amp with a 10" speaker. A lot of places prefer not to fix an amp that you might find a used for $50 or so.

Trying the amp with headphones can help determine if the problem is with the amp or the speaker.

Here is the schematic. It is pretty basic.

 

[Roland GR 88]

L&M prefer to quote high (salesmen aren't techs and quoting too low causes issues obviously) and will sometimes ask for a minimum deposit when the repair cost is likely more than the value of the gear.
This usually prevents them from being stuck with broken stuff that a tech has spent time diagnosing and the customer doesn't want back due to the repair estimate.
I would take it to the store, hand over $100.00 and expect to get back a fixed amp and a few bucks..... Hopefully

 

[wsomar]

An older version of the schematic. (June 1984).
Things to try:
1. Plug in headphones or line out and play. If not distorted, then the preamp is good and the problem is in the amp stage.
2. Remove the front grille and play to make sure it's not rattling.
3. Remove amp from enclosure using 4 screws around the edges. (Not the big ones) and carefully unplug speaker red and black wires. Take special care not to yank and pull the tab form the circuit board loose. Use contact cleaner (available in hardware and electronic stores) to spray all the jacks and pots (knobs). Turn the knobs back and forth to clean the contacts.
4. You can test the speaker (crudely) by placing a AA cell on one speaker wire and touch the other wire to the other side of the battery.

 

[Svante Nygren]

Yippi!
Many thanks, wsomar, you saved my day!!
This schematic is exactly what I searched for. Repair of my old Bloc40B will become so much easier ... although I hope that the problem is mainly oxidized potentiometers. The amp has been in the garage for years, close to a bag of road salt, which didnt exactly seem to help, I had to start vacuum it from salt and corrosion, then use a reasonable amount of WD40..
/Svante

 

[agedhorse]

Never use WD-40 on electronics, that's like using paint thinner instead of oil in a car engine. It might work for a while but will deteriorate faster and worse than before.

 

[Fishheadjoe]

Just an FYI re Yorkville/Traynor support. I have an old Yorkie powered mixer that we use for rehearsals, it's been "acting up" lately.
Given that I live about a mile from the Yorkville mother ship, I ran the mixer over to them.
Firstly, extremely nice people who really care about you, the customer. $60.00 for them to go over the unit with a fine tooth comb, ensuring everything worked as it should. Trn over was less than a week. It's much faster to deal factory direct if possible, rather than through L&M and their internal network.
Just thought I'd throw that out there....
Fishheadjoe

 

[BogeyBass]

Very simple amp
Definitely won't be 200 to fix

Parts shouldn't be more than 10/20 bucks

 

[Canadian APII]

This is a 40W transistorized combo amp with a 10" speaker. A lot of places prefer not to fix an amp that you might find a used for $50 or so.

Trying the amp with headphones can help determine if the problem is with the amp or the speaker.

Here is the schematic. It is pretty basic.

Im an electronics tech, Schematics are not that good for troubleshooting only buying part's. I'd like to see the voltage ranges behind each component. Without that you are relegated to swapping out a component you guessed at then seeing if it worked.

 

[byacey]

Im an electronics tech, Schematics are not that good for troubleshooting only buying part's. I'd like to see the voltage ranges behind each component. Without that you are relegated to swapping out a component you guessed at then seeing if it worked.

A good tech can determine what the voltages should be by looking at the schematic. The schematic also saves a lot of time in troubleshooting by not having to draw out the circuit, and follow traces around on the PC board when taking measurements.

 

[agedhorse]

A good tech can determine what the voltages should be by looking at the schematic. The schematic also saves a lot of time in troubleshooting by not having to draw out the circuit, and follow traces around on the PC board when taking measurements.

Excactly. A qualified tech will be able to look at the schematic, understand how the circuit works and know what voltages to expect. Where a circuit is unconventional, additional information may be provided.

A schematic is not to teach a service technician how to do their work (that should have been done in whatever education they took), but to provide the necessary information to get them started down the correct path.

 

[Canadian APII]

And that takes time. Working on military sonar electronics everything was available to save time. We even gate bashed chips.

 

[byacey]

I guess if money is no object, and time is of the essence, you could just swap assemblies rather than board level troubleshooting, but eventually someone has to know what they are doing to effect a proper repair. Guessing and shot-gun replacement of parts isn't intelligent troubleshooting, and can cause other problems.

My high school electronics instructor was an ex-navy technician, and a very wise individual. I've mentioned this in other posts, but it bears repeating here: He taught me that nothing is truly repaired until you can identify through troubleshooting exactly what component(s) are the problem, followed by replacing the parts and demonstrating normal operation. Remembering this bit of wisdom served me well through post secondary studies and my professional career.

If you guess, sometimes you might guess right, and sometimes wrong. In the military, a wrong guess could cost many lives.