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Author Topic: Trying To Repair a Traynor TBM 25...  (Read 3180 times)

debrad

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Trying To Repair a Traynor TBM 25...
« on: August 20, 2020, 01:24:28 AM »
Hi everyone,

First, thanks for allowing me to join you here.  I have done a lot of fx pedal building and recently completed the conversion of a Filmosound tube-based projector amp but a friend just asked me to look into his SS Traynor amp and it's the first time I have worked with one.

The basic issue is reduced output with a muddy tone and plenty of distortion through the speaker but loud clean output through the headphone jack.  I have verified that the speaker works fine by playing my Traynor YCV40 through it and, thanks to some suggestions on a SS Facebook page, I have also confirmed that the headphone switch/jack is working and that the DC offset is about 6mV.

Last night I found several pads on the PCB that were damaged or broken so I fixed and/or jumpered those and reflowed the solder on EVERY connection.  Low and behold, the speaker output was great for about 5 minutes of testing and then it abruptly switched back to the low mud and distortion.

One of the Facebook members suggested a test of the output transistors and I noticed that the 2 watt 330 ohm resistors and their adjacent diodes get very hot VERY fast and have actually discoloured/burned the PCB around them.  In addition, a light tap on those resistors with a wooden stick also caused a bit of the surface to flake off.

Now, I noticed another member was having heat issues with his TBM-25 and that was another reason why I requested to join this group since I figured he must have gotten those sorted out with your help.

I can attach a copy of the Traynor schematic for this amp once I figure out how to upload a PDF and I am hoping that you might be able to help point me towards a solution to this problem.  In the meantime, I *HOPE* the schematic is still available from the forum post here:

https://www.ssguitar.com/index.php?topic=4354.msg34812#msg34812

I look forward to your replies and thank you in advance!


- brad -

phatt

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Re: Trying To Repair a Traynor TBM 25...
« Reply #1 on: August 20, 2020, 08:46:13 AM »
Q does the speaker switch off when you insert the headphones?
Phil.

debrad

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Re: Trying To Repair a Traynor TBM 25...
« Reply #2 on: August 20, 2020, 11:44:27 AM »
Q does the speaker switch off when you insert the headphones?
Phil.

Yes...the speaker is silent when headphones are plugged into the jack.  The other day I removed the jack entirely, soldered a jumper to make the output connection to the speaker leads, and it was still muddy, distorted, and low volume so the switching jack doesn't appear to be the problem.

With the jack in place, the speaker output is so poor and yet the exact same output running into headphones is so loud and clear.

FYI, the output at the "Line Out" jack sounds just like the speaker...muddy, distorted, and low volume.


Enzo

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Re: Trying To Repair a Traynor TBM 25...
« Reply #3 on: August 20, 2020, 02:09:00 PM »
Perfectly normal for the two 330 ohm resistors to get hot.  Hopefully there is about 7.5v across each of the two diodes.

You say it sounds OK through headphones, but does it still sound OK through the phones with the speaker also connected?  Oh wait, you say the phones makes the speaker silent?  The schematic does not show a cutout, but we can deal.  With speaker connected, how does the line out sound?  Run that to some other amp.  Does the line out sound change when speaker is connected or removed.

You soldered some stuff and it came to life then failed again.  SOunds like you have a bad connection or cracked copper trace somewhere.  Not so much a bad part.  Transistors don't generally die and heal themselves.

debrad

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Re: Trying To Repair a Traynor TBM 25...
« Reply #4 on: August 20, 2020, 05:20:16 PM »
You soldered some stuff and it came to life then failed again.  Sounds like you have a bad connection or cracked copper trace somewhere.  Not so much a bad part.  Transistors don't generally die and heal themselves.

I suppose that's very true!  The fact that I fixed the output...even if just for a moment...certainly gives me hope that I'm making progress.  The downside is that a bad connection or cracked trace might take a while to find...especially since the solder pads seem so fragile on this board!

Perfectly normal for the two 330 ohm resistors to get hot.  Hopefully there is about 7.5v across each of the two diodes.

I measure a 20.2VDC drop across the positive 330 watt resistor and 20.1VDC across the negative.  Then I have -8.2VDC on one side of one diode and +8.00 on the other diode (-0.00 on the other side of both).

With speaker connected, how does the line out sound?  Run that to some other amp.  Does the line out sound change when speaker is connected or removed.

Line Out is muddy and distorted with the speaker plugged in and just as clean as the headphone when I disconnect the speaker


Enzo

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Re: Trying To Repair a Traynor TBM 25...
« Reply #5 on: August 20, 2020, 06:50:47 PM »
OK, that tells me the output stage cannot provide the current the load demands.

You have 8v instead of 7.5 on the supplies, well close enough, it is just a guitar amp, not lab equipment.

verify the two 0.5 ohm 5w resistors associated with the output transistors.  And for that matter, the 150 ohm and 22 ohm resistors associated with the drivers.

From the speaker on the schematic, follow the output line to the left and you come to 10 ohm R124.  Is it open or burnt?

debrad

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Re: Trying To Repair a Traynor TBM 25...
« Reply #6 on: August 20, 2020, 10:24:47 PM »
Interesting...so the headphone output sounds clear because there's enough current for that particular load?

I did some quick measurements:

R125 should measure 10 ohms and it does...with no signs of burns or broken traces

R122 and R123 are the 0.5 ohm 5 watt resistors and they measure 0.5 ohm

R120 should measure 22 ohms and it measures 21.9 ohms

R119 and R121 should measure 150 ohms and they measure 148.6 (R119) and 150 (R121)

phatt

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Re: Trying To Repair a Traynor TBM 25...
« Reply #7 on: August 20, 2020, 10:46:44 PM »
All seems to point to a speaker failure,,, maybe test using another speaker.
Phil.

debrad

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Re: Trying To Repair a Traynor TBM 25...
« Reply #8 on: August 21, 2020, 11:08:00 PM »
The speaker tested OK a few days ago but your response made me think I should test it again.  I connected another amp to the TBM-25's speaker and it sounded fine.

I also connected the TBM-25 to two separate speaker cabs and it sounded just as bad as it does connected to its own speaker.

Finally, I soldered new speaker wire to the TBM-25's circuit board and ran that to the speaker and it still sounded bad.

Looks like the problem still lies within the amp somewhere...

- brad -

Enzo

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Re: Trying To Repair a Traynor TBM 25...
« Reply #9 on: August 21, 2020, 11:55:26 PM »
Just noticed a drawing error.  The two output transistors are drawn wrong, they have swapped base and collector connections.

Quite possible one of those two parts is bad.

debrad

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Re: Trying To Repair a Traynor TBM 25...
« Reply #10 on: August 23, 2020, 11:03:21 AM »
I tried measuring resistance across the Base/Collector/Emitter of the two 2SC2233 output transistors without removing them from the board and Q7 behaved fairly well but the meter never really seemed to settle on Q8 and, aside from the 150 ohms across the base and emitter (pin 1 & pin 3), the values were something like 300 mega-ohm.

I guess I should really pull them from the circuit and test them properly...but, as Enzo pointed out, it seems hard to believe they were damaged, then roared to life after I re-flowed all the solder pads, and then spontaneously died again...but maybe that points to the issue...
« Last Edit: August 23, 2020, 11:21:21 AM by debrad »

debrad

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Re: Trying To Repair a Traynor TBM 25...
« Reply #11 on: August 26, 2020, 11:29:33 AM »
My apologies...I still haven't pulled the output transistors from the circuit so that I could test them properly; however, after watching a solid state amp repair by D-Labs on YouTube, I decided to do a quick collector voltage measurement on the two 2SC2233 trannies just like he did.  The one with the more stable resistance measurements (Q7) measures 0.528V while the one with the wandering resistance measurements (Q8) measures -28.3V...I assume they should be a little closer to the same value

g1

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Re: Trying To Repair a Traynor TBM 25...
« Reply #12 on: August 26, 2020, 01:40:29 PM »
I decided to do a quick collector voltage measurement on the two 2SC2233 trannies just like he did.  The one with the more stable resistance measurements (Q7) measures 0.528V while the one with the wandering resistance measurements (Q8) measures -28.3V...I assume they should be a little closer to the same value
Sounds like you measured the emitters, not the collectors.
There is no reason to assume they should be closer in value.  Unless D-labs was working on the same model amp (or at least configuration, quasi-complimentary), his readings have nothing to offer you as far as reference values.

debrad

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Re: Trying To Repair a Traynor TBM 25...
« Reply #13 on: August 26, 2020, 03:29:17 PM »
My apologies...I SWEAR the datasheet I had showed the collector on Pin1 but it looks like the 2SC2233 goes: 1-Base, 2-Collector, 3-Emitter.

 :-[  :-[  :-[

Given that, my measured voltages are:

Q7
B=0.528
C=28.88
E=0.011

Q8
B=-28.3
C=0.011
E=-29.06

Reasonable?  Helpful?

- brad -

Enzo

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Re: Trying To Repair a Traynor TBM 25...
« Reply #14 on: August 26, 2020, 09:44:20 PM »
Those voltages look fine for idle DC levels, but they don't tell us if the parts can conduct current well.

You can probably find 2SC2233, or the common TIP41C would likely work fine too.