Markbass head - loss of volume on start up

[muso]

L O guys - any tech heads able to help with this ????

Have owned a Markbass SA450 (digital switching transformer) bass head for a couple of years - now out of warranty - has been suffering from little or no volume when switched on from "cold" and has taken up to 10 minutes to get to the level set by the input/output gains.Once the volume has got to the right level it runs fine...seems to behave like an old valve radio, needing time to warm up!!!
The head has had two power modules fitted in the last year - 1st was to rectify loss of volume (which didnt cure it), 2nd was when the power module blew up. An EQ pot was replaced as "faulty" as well. All work done by Markbass UK official repairer - They've been very helpful but have been unable to trace any fault with the unit regarding the loss of volume. The fault goes where the head goes - using any other head with same bass/leads/cab has no problem.....have used all 6 of my basses to test and the fault is always when the SA450 is used. any thoughts would be useful as I've spent alot of £££...Ta

[MarkBassChat]

I think that you meant switch mode power supply (SMPS) - it has nothing in common with digital. Clearly the problem is related to the amp - most probably to the power supply. Due to the complexity of the power supply it is quite often replaced and not fixed when it fails. Fixing it is possible but time consuming - which makes it more expensive. So the fact that service replaced the board (instead of fixing it) is quite normal. But I'm confused with what you wrote:
[quote name='muso']
They've been very helpful but have been unable to trace any fault with the unit regarding the loss of volume.[/quote]
How this is possible? This is a basic task to be done and in fact it is very simple (using a generator and an oscilloscope). I would say that they rather didn't want to spend any time on this task. I would contact Markbass Italy directly saying that official service in UK cannot help you. They could be interested in finding what exactly was the failure. At least I would try.

Mark

Edited September 24, 2012 by MarkBassChat

[muso]

Thanks for the info - I have emailed Markbass direct and they have asked for a full detailed description of the fault as it is not on the list of known faults ( according to the UK distributor, who have also emailed them for advice).

[andreapenna]

Just my h.o.,

Why not taking a video instead of just words in the email?
There will be no risk of explanation/interpretation of the fault.

Andrea

[muso]

Yes they've previously been sent video/sound footage of the failure - finally Markbass directed the reparier to freeze the unit (!!) and they managed to recreate the fault...hooray!!!! apparently the fault lay with the resistors in the preamp - this is not on Markbass's list of known faults (it is now!) so be warned - if you own any markbass heads/combos and start getting problems with start up volume you know what it is now....

[chrismuzz]

That sounds bizarre! Glad they've got to the bottom of it though, and I hope you get your amp back soon. Hey, this thread may help someone else someday

[muso]

Hope this thread does get to other users of Markbass - I mean the gear sounds great and is highly portable but apparently this switchmode technology was developed by Gallien Kruger in the late 80's which made bass gear extremely light but reliability was not good. I did see on one electronics website/blog comment that the "lifespan of this type of technology is unknown..."

[Stevesbass]

I had the same problem last weekend turned my 121h combo on and had really low output.. turned it off and back on again and hey presto it seemed to be ok?..I had just come into a warm room from the cold outside and assumed it was maybe some kind of temperature issue.. with the winter fast approaching I hope this was a one off occurrence!

[Jakester]

1 hour ago, Stevesbass said:

I had the same problem last weekend turned my 121h combo on and had really low output.. turned it off and back on again and hey presto it seemed to be ok?..I had just come into a warm room from the cold outside and assumed it was maybe some kind of temperature issue.. with the winter fast approaching I hope this was a one off occurrence!

This is very interesting as I was using my 121P yesterday and suddenly had a huge drop in volume. I’d assumed it was the battery in my bass, so replaced that in the break and then it cut out as I’d upped the gain to compensate for the much lower passive signal. Turned off and on and with the gain reduced it was then fine for the rest of the gig. 
 

No discernible change in temperature though -  there was first thing but it lasted a good hour and a half of playing before it went. I’ll keep an eye on it now!

[Jakester]

On 21/10/2019 at 15:01, Jakester said:

This is very interesting as I was using my 121P yesterday and suddenly had a huge drop in volume. I’d assumed it was the battery in my bass, so replaced that in the break and then it cut out as I’d upped the gain to compensate for the much lower passive signal. Turned off and on and with the gain reduced it was then fine for the rest of the gig. 
 

No discernible change in temperature though -  there was first thing but it lasted a good hour and a half of playing before it went. I’ll keep an eye on it now!

Had this happen again this weekend, and i think in hindsight it is down to a change in temp - amp came out of ‘mancave’ into car and pressed straight into service and started cutting out. Cranked it up and suddenly came back to life, deafening everyone around me! Turned off and on again, and worked fine thereafter. 
 

Looks like a call to the distributor... 😭

[Grantus]

Well, well thought I was the only one to experience this issue - good to hear the same symptoms. Little Mark II Bass amp does exactly the same thing - needs about 10 to 15 minutes before it produces any real output, as such I have been turning it on prior to actual performance. I have been very conscientious of a possible failure mid gig so I now carry a spare. Difficult to believe this can be due to a passive component in the pre-amp section - thought it would have to be a SMPS problem but I will be guided by better brain surgeons than me. 

[BassBunny]

My SA450 is experiencing similar symptoms but doesn't recover. The Volume has been dwindling gig by gig. When I set it up on NYE it sounded like a 15w practice amp. The estimate from Real, ( MB official repairers ), is likely to be greater than the value of the amp. 

I caught a posting about MarkBass repairs on FaceBook and apparently Gee Electronics, in Warrington, are happy to look at them so it's been with them since last Tuesday. Called yesterday and it's on a "soak test" for the weekend so I get the impression it could be sorted. Let's see what happens when I go and pick it up.

 

[Jakester]

5 hours ago, BassBunny said:

 

I caught a posting about MarkBass repairs on FaceBook and apparently Gee Electronics, in Warrington, are happy to look at them so it's been with them since last Tuesday. Called yesterday and it's on a "soak test" for the weekend so I get the impression it could be sorted. Let's see what happens when I go and pick it up.

 

Following with interest as I haven’t yet sent to Real as it’s been in use. I’m expecting repair costs to be high, so if someone else might be cheaper, I’d love to know!

[BassBunny]

I contacted Real before taking it to Real and their prices are:

£35 to diagnose the problem, which you get back if you go ahead. £69 fixed labour, £18 courier fee to send it back + parts. I am pretty sure they don't repair to component level, so parts would be a new PCB. 

I'm not sure if VAT needs adding to that. I know a couple of people who have had MB products fixed by them and the overall cost was between £170 and £200.

[BassBunny]

Just been to Gee Electronics and picked the amp up. They tested it and indeed it was low on power. It was initially diagnosed as corroded jacks in the Send/Receive circuit so it has now been given a full service, (All jacks cleaned or replaced, all pots, switches and connectors cleaned. Some suspect solder connections on the main pcb were re-soldered and then it was soak tested twice for 2 hrs each time. 

Now been given a clean bill of health and work guaranteed for 3 months. I'll get to test it out over the next day or so.

[bkinder]

i have 2 markbass combos experiencing this same behavior, low volume, maybe it will come back up if you leave it on, maybe it won't.

I'd say that this has to now be a "KNOWN" issue with the amps if it's happening this frequently.  I'm getting ready to take them in for repair and will direct the repairman to this site so he has a little information regarding this now "KNOWN" issue.

[BassBunny]

2 hours ago, bkinder said:

i have 2 markbass combos experiencing this same behavior, low volume, maybe it will come back up if you leave it on, maybe it won't.

I'd say that this has to now be a "KNOWN" issue with the amps if it's happening this frequently.  I'm getting ready to take them in for repair and will direct the repairman to this site so he has a little information regarding this now "KNOWN" issue.

To be fair, mine had given me 12 years faultless service before it started causing issues.

The problem is if you take it to anyone other than Real Electronics, they won't be able to do anything with it as MarkBass won't release the circuit diagrams. Also the later ones are Class D power sections and pretty much irreparable. It's a board swap at around £200. 

Someone on here did get one sorted, a Class A/B one and I think I have the repair guy details. I'll try and dig them out.

Drop @johnny2shoes a message. Someone in Bolton sorted his but I believe it was terminal and not a volume drop.

Edited November 10, 2020 by BassBunny