Marshall guitar amp TDA1514A repair issues

A friend and I (mostly him!) had the unpleasant task of repairing a Marshall Valvestate 8240 amp recently. It had a number of problems including dry joints, failed regulators and a blown amp. The repair was going swimmingly until we replaced the TDA1514A chip amp. Upon application of power – the replacement unit would literally explode – I’m talking chunks of plastic flying out of the amp!
I’d ordered the part from a Hong Kong supplier on ebay. I contacted them, they sent a replacement unit and the same happened again. They were good enough to refund me without me returning the parts despite not being able to suggest any reason for the failures.

Marshall Valvestate 8240

Browsing the web for clues I found a couple of links that appeared related:

Crucially, the first link mentioned fake parts. With this is mind I tried two more UK suppliers specifically asking that they guarantee their parts were genuine – both said they did guarantee this and guess what? Both failed. By this time we were wise to the explosions, so had rigged up the old light bulb current draw test and variac to avoid losing any eyes or gaining life-changing scars. Again, both suppliers refunded. Eventually (and this is where I hang my head in shame for it not being my first port of call) I contacted Marshall who were incredibly helpful. They told me that they themselves had experienced problems with supplies of this exact part and that they had located a source of new old stock to get around it. What is not clear is whether in some later revision to these chips, the unusual way in which Marshall implements them causes a problem. I guess it’s that or the fact that these were all fakes – though I can’t believe the fakes wouldn’t work in some application. We didn’t have the energy to test that.

The difference in appearance between the failing parts and the new old stock is pretty clear (ignore the cut legs on the good part):

TDA1514A. Known good part on the left, bad part on the right

Should you experience this problem, I would advise you to go straight to Marshall and they will provide you with a working component. At time of writing, they can be contacted as follows:

Lee Bates lbates@marshallamps.com
Marshall Amplification plc.
Denbigh Road,
Bletchley,
Milton Keynes,
MK11DQ.

Spares Department telephone:
01908 375411

Electronics - Pete

Pete beavering away on the Marshall 8240

Special gratitude goes to Pete for his efforts on this repair – it really did chew up some hours whilst we tried to work out what was causing the fireworks.

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10 Comments

Filed under Geeky stuff

10 responses to “Marshall guitar amp TDA1514A repair issues

  1. Adam Hurley

    Hi guys thanks for creating this web page I too have had problems with the fake chips and got a refund on them it blew a chunk right out of the centre of the chip.
    I sent an Email to lee bates who replied to me promptly and I am awaiting to see the result of my inquiries.

  2. Hey Adam. That’s really great news. I’m glad that this article has been so useful, so quickly.

    Dan

  3. Claudio

    Hello there,
    The TDA1415A is discontinued. The AQ version is stereo. Not suitable in replacement of the A.
    I had the same problem at 2 years. I replaced one of the 2 TDA1514A and it blown again. But after looking more to the others componants, I saw that the Zener of the concerned TDA1514A was broken. It falled in pieces. It is a blue small zener diode for a value of 6V8. It is cheap to buy and easy to replace. Try to get off and test it with a multi meter with Diode tester. And replace the TDA too. Becarefull when you change the TDA : Do not cut the lugs to get the TDA off of the board because you can short circuit 2 lugs so you can dammage the other componants. You will find the schematics of this amp at : http://www.drtube.com/schematics/marshall/8240-61.gif
    This amp has 2 amps. One for the left side and another one for the right one. So if the left side TDA blew, you must check the ZENER ZD1. If it is the right one, check the ZD2. ZD1 and ZD2 must be indicated on the upper side of the circuit bord of your amp. There are one on the right side of each radiators (When pots are closed to you), if I remember well. I bought 3 TDA on EBay for 20 euros from Hong Kong (Not China). I placed one and keep the 2 others in case of… I am sure you can find the genuine one.
    This amp is dicontinued, that’s why Marshall does not care of you. They said : “Buy another one”. If you have any question, just reply.

    Claudio, France

    • Claudio, thanks for your reply. I cannot agree with you about Marshall. Their service here in the UK was fantastic and that is much of the point of this article – after all they sold me the genuine working part that I could not buy elsewhere. Perhaps the service in France is worse, but please be clear about your experience.

      Also, at time of writing, your link is broken.

      Thanks,

      Dan

  4. Marshall parts and technical support is no longer under the auspices of Korg. U.S. Music has taken over Marshall support the last few months. As of December 7, 2010 U.S. Music had whole amps but had not yet received the parts from Korg. So all of the Marshall service centers in the world will be delayed getting parts.

  5. Jim Spielmaker

    Thanks for the tip. I recently purchased a TDA1514A from mcmelectronics.com to repair a Fender Frontman 25R Amp. It had the Phillips logo on it but also had Taiwan on it. It blew as soon as power was applied. I replaced it with the NTE replacement (NTE7118) and it came up and worked fine. I have yet to see if mcmelectronics will refund the money.

  6. Joe Tur

    http://www.nteinc.com/ You can find a list of all the distributors of various items, cross ref lists, & all sorts of stuff here

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