diff --git a/src/emu/ioport.cpp b/src/emu/ioport.cpp
index 6f751a28dad..4d106912d7b 100644
--- a/src/emu/ioport.cpp
+++ b/src/emu/ioport.cpp
@@ -634,6 +634,8 @@ ioport_field::ioport_field(ioport_port &port, ioport_type type, ioport_value def
 				if (device().subtag(def->tag) == fulltag && def->mask == m_mask)
 					m_defvalue = def->defvalue & m_mask;
 		}
+
+		m_flags |= FIELD_FLAG_TOGGLE;
 	}
 }
 
@@ -706,6 +708,24 @@ const input_seq &ioport_field::defseq(input_seq_type seqtype) const
 }
 
 
+//-------------------------------------------------
+//  set_defseq - dynamically alter the default
+//  input sequence for the given input field
+//-------------------------------------------------
+
+void ioport_field::set_defseq(input_seq_type seqtype, const input_seq &newseq)
+{
+	const bool was_changed = seq(seqtype) != defseq(seqtype);
+
+	// set the new sequence
+	m_seq[seqtype] = newseq;
+
+	// also update live state unless previously customized
+	if (m_live != nullptr && !was_changed)
+		m_live->seq[seqtype] = newseq;
+}
+
+
 //-------------------------------------------------
 //  type_class - return the type class for this
 //  field
@@ -3112,13 +3132,6 @@ ioport_configurer& ioport_configurer::onoff_alloc(const char *name, ioport_value
 	// allocate a field normally
 	field_alloc(IPT_DIPSWITCH, defval, mask, name);
 
-	// special case service mode
-	if (name == DEF_STR(Service_Mode))
-	{
-		field_set_toggle();
-		m_curfield->m_seq[SEQ_TYPE_STANDARD].set(KEYCODE_F2);
-	}
-
 	// expand the diplocation
 	if (diplocation != nullptr)
 		field_set_diplocation(diplocation);
diff --git a/src/emu/ioport.h b/src/emu/ioport.h
index a9a4d49b0c4..a5169e08c21 100644
--- a/src/emu/ioport.h
+++ b/src/emu/ioport.h
@@ -1058,6 +1058,8 @@ public:
 	const input_seq &seq(input_seq_type seqtype = SEQ_TYPE_STANDARD) const;
 	const input_seq &defseq(input_seq_type seqtype = SEQ_TYPE_STANDARD) const;
 	const input_seq &defseq_unresolved(input_seq_type seqtype = SEQ_TYPE_STANDARD) const { return m_seq[seqtype]; }
+	void set_defseq(const input_seq &newseq) { set_defseq(SEQ_TYPE_STANDARD, newseq); }
+	void set_defseq(input_seq_type seqtype, const input_seq &newseq);
 	bool has_dynamic_read() const { return !m_read.isnull(); }
 	bool has_dynamic_write() const { return !m_write.isnull(); }
 
diff --git a/src/frontend/mame/ui/info.cpp b/src/frontend/mame/ui/info.cpp
index 9de81cef6ec..93583ed85df 100644
--- a/src/frontend/mame/ui/info.cpp
+++ b/src/frontend/mame/ui/info.cpp
@@ -30,6 +30,7 @@ machine_info::machine_info(running_machine &machine)
 	m_has_dips = false;
 	m_has_bioses = false;
 	m_has_keyboard = false;
+	m_has_test_switch = false;
 
 	// scan the input port array to see what options we need to enable
 	for (auto &port : machine.ioport().ports())
@@ -43,6 +44,8 @@ machine_info::machine_info(running_machine &machine)
 				m_has_analog = true;
 			if (field.type() == IPT_KEYBOARD)
 				m_has_keyboard = true;
+			if (field.type() == IPT_SERVICE)
+				m_has_test_switch = true;
 		}
 
 	for (device_t &device : device_iterator(machine.root_device()))
@@ -51,6 +54,24 @@ machine_info::machine_info(running_machine &machine)
 }
 
 
+//-------------------------------------------------
+//  find_dipname - look up DIP switch by name
+//-------------------------------------------------
+
+ioport_field *machine_info::find_dipname(const char *name) const
+{
+	if (!m_has_dips)
+		return nullptr;
+
+	for (auto &port : m_machine.ioport().ports())
+		for (ioport_field &field : port.second->fields())
+			if (field.type() == IPT_DIPSWITCH && strcmp(field.name(), name) == 0)
+				return &field;
+
+	return nullptr;
+}
+
+
 /***************************************************************************
     TEXT GENERATORS
 ***************************************************************************/
diff --git a/src/frontend/mame/ui/info.h b/src/frontend/mame/ui/info.h
index 21d920e4131..b31726ba27f 100644
--- a/src/frontend/mame/ui/info.h
+++ b/src/frontend/mame/ui/info.h
@@ -29,6 +29,9 @@ public:
 	bool has_dips() const { return m_has_dips; }
 	bool has_bioses() const { return m_has_bioses; }
 	bool has_keyboard() const { return m_has_keyboard; }
+	bool has_test_switch() const { return m_has_test_switch; }
+
+	ioport_field *find_dipname(const char *name) const;
 
 	// text generators
 	std::string warnings_string();
@@ -46,6 +49,7 @@ private:
 	bool                    m_has_dips;
 	bool                    m_has_bioses;
 	bool                    m_has_keyboard;
+	bool                    m_has_test_switch;
 };
 
 class menu_game_info : public menu
diff --git a/src/frontend/mame/ui/ui.cpp b/src/frontend/mame/ui/ui.cpp
index d7bf97a6562..a21b1e82cee 100644
--- a/src/frontend/mame/ui/ui.cpp
+++ b/src/frontend/mame/ui/ui.cpp
@@ -256,6 +256,13 @@ void mame_ui_manager::initialize(running_machine &machine)
 	{
 		slider_current = nullptr;
 	}
+
+	if (!m_machine_info->has_test_switch())
+	{
+		ioport_field *service_mode_sw = m_machine_info->find_dipname(ioport_configurer::string_from_token(DEF_STR(Service_Mode)));
+		if (service_mode_sw != nullptr)
+			service_mode_sw->set_defseq(machine.ioport().type_seq(IPT_SERVICE));
+	}
 }