Help me fix my Manson electronics ...

blobb · May 2023

I've had this one while. The electrics don't work, and I'd love to get it workibg .... but... I don't know what it is supposed to do!

I messaged Hugh Manson about it a few years ago, he said he would look at it but life got in the way, and now he has retired.

I know a decent electronics chap who fixes up old hi-fi and the like so my plan is to get it over to him to see if he can reverse engineer the circuits. But you lot know everything - so long as I don't want to buy a car I reckon it's worth a shout out to the hive mind.

So here goes, I'll let the pictures do the talking:

1. Front. 3x brass knobs, jack socket, Line of 3 micro switches (3 way / 2 way / 3 way), 2 other micro switches (2 way / 3 way). blanked off micro switch hole (no idea if ever had anything in it). 2x KA Rainbow humbuckers.

Image: https://live.staticflickr.com/1939/44972149971_30f3ef3ec2_k.jpg

2. circuit in situ. It is powered by 2x 9v batteries

Image: https://live.staticflickr.com/65535/52902423887_e5f348c684_k.jpg

3. Flip side.

Image: https://live.staticflickr.com/65535/52903156954_643a7bc304_k.jpg

Image: https://live.staticflickr.com/65535/52903383195_983ffc31af_k.jpg

There appear to be 2x chips in there and what could be 5x trim pots (?), the fifth one is to the side of the microswitch on the right. These are accesible from the top side with a small screwdriver slot on each pot.

Pots are corroded, middle one more than the other two. They spin ok.

On the left of picture, next to the 2x micro switches see 3x holes and a green cap? That corresponds to the filled in hole on the front. Could have been original switch but the board didn't look like it had ever been removed but I will never know.

No sound with fresh batteries but I can get a faint clean signal if I wiggle the jack in the socket.

Hugh said he remembers doing something that resembles this but he only saw pictures of the top of the board. Could be EQ, power stage or one of his first attempts at building effects in (so probably some sort of fuzz circuit). My other Manson has switches but no circuit. That has phase and coil splits so imagine these feature as well.

Where to start? If it's gash then I'll rip it out and put something else in there (suggestions?). If nothing else something for us to chew fat about.

Ok - over to you lot, what's the prognosis doc?

blobb · May 2023

Image: https://live.staticflickr.com/65535/52902423902_eef03814e4_k.jpg

Winny_Pooh · May 2023

Wow, that is complex, too complex to diagnose over distance IMO.

Pot switch cleaner? Do that for everthing then you'll need a multimeter: start by checking voltage from the battery is going in ok, continuity on the pots, continuity on the input from pickups and output signals from preamp but after that it's a case of inserting audio and tracing where it fails within the circuit. Google circuit tester.

If none of this sounds familiar take it to a repair person. Someone who fixes pedals or amps can handle it.

Funkfingers · May 2023

Might be worth finding out who Quinn is/was and trying to obtain a schematic diagram.

Danny1969 · May 2023

To me it looks like a pre amp circuit and active EQ and could be effects as well although I would expect to see a discrete transistor and some diodes for fuzz.
The larger chip looks like a quad opamp and the smaller one is likely a dual opamp. These provide the gain and the resistors and caps form filters which is how the EQ is manipulated.

Any electronics guy can repair this as it's very basic stuff but if you want to have a go yourself start by reseating that opamp in it's holder. Clean all pots and switches. Look at the solder joints and redo any bad ones. Then make sure you have volts on the opamps. I would expect the 2 batteries form a dual supply so 18V between the opamps + and - pins but 9V with respect to ground.

impmann · May 2023

Looks like its had some significant rework at some point - there's a lot of scruffy solder on the back, with some splatter that won't be helping.
That switch that is missing/blanked has been bypassed/hardwired underneath.
The socket looks pretty corroded. I'd start by spraying switch cleaner into it and working a jack in and out to clean up the contacts. Then apply switch cleaner to all the switches (and work them back n forth). As has been said, remove and reseat the Op Amps (the legs can get corroded - and the action of removing them and refitting can scrape that off). Then try again...

blobb · May 2023

I can't find any reference to QUINN. I know Hugh got his electrics hand built by his mate, but I don't know any more than that. He would be the guy to speak to.

I've got this guy that fixes hi-fi, he knows what he is doing but I'm not sure what he knows about guitar 'logic' so these comments will help when I attempt to describe it's function.

The two batteries look like one is routed to the board (+ / - next to QUINN) the other routes to the jack socket.

I wondered if the blank microswitch may have been an indicator LED? There is a small tube in the hole - you can just see it on the third picture, left most hole with the star washer over it. Unless this was fitted later, I can't see getting a switch through the hole with the tube in place.

what would the trim pots do? Are they trim pots? The screw rotates the contact ring between the two white dots and the ring stops, the screw continues to rotate until you reverse and the ring moves to the other white dot and stops. So some sort of limited adjustment between two fixed points. And why would you need five of them? These adjusters can only be accessed with the back off so 'set and forget'.

I think the red micro switch is pickup selector. With cable half inserted I can get some sound and the switch selects pup.

The 3x micros would be possibly coil splits and phase - I have a similar arrangement on my other Manson. One switch per pup and a third one to switch phase (which only works with both pups selected). That leaves the bottom micro which from what I'm reading here makes me think active pups (small chip) with a boost circuit (large chip). Active eq would need three adjusters (as on my Ibanez tri-sound). So master vol and 2x tone knobs.

Funkfingers · May 2023

Trim pots could perform all manner of tasks. e.g. Governing a switchable signal boost, setting an active EQ frequency peak or bandwidth, setting an onboard compression ratio or attack/release time. Much depends on the functions of the IC chips. Pity that no identifying legend appears on them.

The function of the micro lever switches might be discernible if the connections between their contacts were known.

thermionic · May 2023

Send it to Mend It Mark!

impmann · May 2023

Andy Baxter has got a Merlin Active bass in at the moment - its a different shaped board but looks like its made of the same material. No sign of an LED on that one, though... but I wonder if the EQ circuit is similar, and may help?

https://www.andybaxterbass.com/products/1982-manson-merlin-bass-mahogany

blobb · May 2023

^^ interesting. Great find, it does look like a cut down version of the same circuit. Presumably pickup selector / master vol / 2x coil split switches / 1x phase select and dedicated 'tone' for each pickup. Great. If I assume that logic applies to my circuit, that leaves me with 1x unidentified switch and the mystery blank switch / LED. Could be the extra switch brings in the additional boost circuit?

2x trim pots on board and perhaps the pots have trim on them? Is this a common 'pot' thing? If so what do they trim? If that's the approach on the bass it would make sense as I've got 5x trims. Which would match the 2+3 pot trims on the bass (you can't access the back side of the pots on mine). .

I see the bass is also using 2 batteries for 18v supply.

I'm going to see if hi-fi guy is in his workshop this weekend so loads of info to pass on to help explain what this thing does.

cheers for your help so far.

blobb · May 2023

Gary from The Vintage Audio Co is on the case - and is reading this thread. If anyone else has any info to share we can go direct!

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Help me fix my Manson electronics ...

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